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GEOLOGICAL DISASTERS AND SURFACE RUPTURES OF JANUARY 23, 2024 MS7.1 WUSHI EARTHQUAKE, XINJIANG, CHINA ZHANG Bo-xuan, QIAN Li, LI Tao, CHEN Jie, XU Jian-hong, YAO Yuan, FANG Li-hua, XIE Chao, CHEN Jian-bo, LIU Guan-shen, HU Zong-kai, YANG Wen-xin, ZHANG Jun-long, PANG Wei SEISMOLOGY AND GEOLOGY    2024, 46 (1): 220-234.   DOI: 10.3969/j.issn.0253-4967.2024.01.013 Abstract （785）   HTML （20）    PDF（pc） （14676KB）（569）       Knowledge map    Save The MS7.1 earthquake in Wushi, Xinjiang on January 23, 2024, represents the largest earthquake in the Tianshan seismic belt since the 1992 Suusamyr MS7.3 earthquake in Kyrgyzstan. Preliminary precise aftershock localization and initial field investigations indicate an NE-trending aftershock zone with a length of 62km that is concentrated at the mountain-basin transition area. This event produced geological hazards, including slope instability, rockfalls, rolling stones, and ground fissures, primarily within a 30-kilometer radius around the epicenter. The epicenter, located approximately 7 kilometers north of the precise positioning in this study, witnessed a rapid decrease in geological hazards such as collapses, with no discernible fresh activity observed on the steep fault scarp along the mountainfront. Consequently, it is inferred that the causative fault for this main shock may be an NW-dipping reverse fault, with potential rupture not reaching the surface. Moreover, a surface rupture zone with a general trend of N60°E, extending approximately 2 kilometers, and displaying a maximum vertical offset of 1m, was identified on the western side of the micro-epicenter at the Qialemati River. This rupture zone predominantly follows the pre-existing fault scarp on higher geomorphic surfaces, indicating that it is not new. Its characteristics are mainly controlled by a southeast-dipping reverse fault, opposite in dip to the causative fault of the main shock. The scale of this 2-kilometer-long surface rupture zone is notably smaller than the aftershock zone of the Wushi MS7.1 earthquake. Further investigation is warranted to elucidate whether or not the MS5.7 aftershock and the relationship between the SE-dipping reverse fault responsible for the surface rupture and the NW-dipping causative fault of the main shock produced it. Table and Figures | Reference | Related Articles | Metrics

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TYPICAL CASE ANALYSIS ON SETBACK DISTANCE FOR URBAN BURIED ACTIVE FAULT: AN EXAMPLE SITE ALONG THE TANLU FAULT ZONE IN XINYI CITY CAO Jun, LI Yan-bao, RAN Yong-kang, XU Xi-wei, MA Dong-wei, ZHANG Zhi-qiang SEISMOLOGY AND GEOLOGY    2022, 44 (4): 1071-1085.   DOI: 10.3969/j.issn.0253-4967.2022.04.016 Abstract （989）   HTML （73）    PDF（pc） （11099KB）（522）       Knowledge map    Save With the acceleration of urbanization process, solving the earthquake and its associated disasters caused by buried active fault in urban areas has been a difficult issue in the construction of urban public security system. It is difficult to deal with the anti-seismic issues of cross-fault buildings using the existing techniques, therefore, reasonable setback distance for buried active fault in urban area is the only method for the planning and construction at the beginning. At present, theoretical research about setback for active fault is becoming more and more mature, and the mandatory national standard “Setback distance for active fault” will be enacted soon. As a result, how to work on the basis of these theories and national standards is in urgent. In recent years, the exploration of urban active faults was successively completed. However, there are no typical cases of how to make full use of the achievements of urban active fault projects in the follow-up work, and how to guide urban construction based on the project conclusions, so as to ensure urban safety and rational development of urban economy. In this paper, taking a site along the Anqiu-Juxian Fault in the Tanlu fault zone in Xinyi city as an example, based on the results of 1︰10 000 active fault distribution map, and referring to the stipulation of national standard “Setback distance for active fault”, 12 shallow seismic survey lines with a spacing of less than 50m were laid out firstly, and the results of shallow seismic exploration show the existence of two high-dip faults in the site. Secondly, considering the shallow seismic survey results and the geologic site conditions, five rows of borehole joint profiles were selected along five of the shallow seismic survey lines. Based on the location of the faults and stratigraphy in the site revealed by the borehole joint profiles, and considering the latest research results of Quaternary stratigraphy and the conclusion of urban active faults detection, the west branch fault is constrained to be a Holocene active fault and the east branch fault is an early Quaternary fault. As a result, we precisely mapped the trace, dip and upper breakpoint of the fault in the site based on the shallow seismic exploration and joint borehole profile. The accurate positioning of the plane position of the active fault differs by about 200m from the 1:1000 strip distribution map. According to the relevant national standards and scientific research results, active faults in the site shall be avoided. Based on the surface traces of active faults revealed by the accurate detection in the site, the active fault deformation zone was delineated, and the range of setback distance for active fault was defined outside the deformation zone. The detection results accurately determined the plane distribution of the active fault in the site, which meets the accuracy of the development and utilization of the site. Based on the accurately located active fault trace, and complying with the forthcoming national standard “Setback distance from active fault”, this study not only scientifically determines the setback distance for active fault in the site, but also releases the scarce land resources in the city. This result achieves the goal of scientifically avoiding potential dangerous urban hidden active fault and making full use of land. The case detection process confirms that the results of urban active fault detection are still difficult to meet the fault positioning accuracy required for specific site development, and the range of active fault deformation zone within the site must be determined based on the precise positioning method for hidden active faults as stipulated in the national standard “Setback distance for active fault”. The national standard “Code for seismic design of buildings” only specifies the setback distance for active faults under different seismic intensity, but does not provide any clear definition of the accuracy of active fault positioning, so it is difficult to define the required active fault positioning degree and boundary range of the deformation zone of active fault in practice. The national standard “Setback distance for active fault” clearly defines various types of active fault detection and positioning methods, determines the scope of active fault deformation zone and the accurate setback distance for active fault in different cases. The specific case proves that before developing and utilizing specific sites along urban concealed active faults, relevant work shall be carried out according to the national standard “Setback distance for active fault” to effectively resolve the issue about the relations between urban development and urban safety, so the promulgation and implementation of national standard should speed up. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE LATE QUATERNARY ACTIVITY OF THE WEST XIADIAN FAULT IN BEIJING PLAIN SHEN Jun, DAI Xun-ye, XIAO Chun, JIAO Xuan-kai, BAI Qilegeer, DENG Mei, LIU Ze-zhong, XIA Fang-hua, LIU Yu, LIU Ming SEISMOLOGY AND GEOLOGY    2022, 44 (4): 909-924.   DOI: 10.3969/j.issn.0253-4967.2022.04.006 Abstract （446）   HTML （57）    PDF（pc） （12117KB）（470）       Knowledge map    Save Beijing plain is a strong earthquake tectonic area in China, where the Sanhe-Pinggu earthquake with M8 occurred in 1679.The seismogenic fault of this earthquake is the Xiadian Fault. An about 10km-long earthquake surface fault is developed, striking northeast. Deep seismic exploration reveals that this surface fault is a direct exposure of a deep fault cutting through the whole crust, and it is concealed in the Quaternary layers to both ends. Previous studies have not yet revealed how the deep fault with M8 earthquake extended to the southwest and northeast. In the study of Xiadian Fault, it is found that there is another fault with similar strike and opposite dip in the west of Xiadian Fault, which is called the West Xiadian Fault in this paper. In this study, six shallow seismic profiles data are used to determine the location of this fault in Sanhe city, and the late Quaternary activity of the fault is studied by using the method of combined drilling, magnetic susceptibility logging and luminescence dating. The results of shallow seismic exploration profiles show that the fault is zigzag with a general strike of NE and dip NW. In vertical profile, it is generally of normal fault. It shows the flower structure in one profile, which indicates that the fault may have a certain strike-slip property. On two long seismic reflection profiles, it can be seen that the northwest side of the fault is a half graben structure. This half graben-like depression, which has not been introduced by predecessors, is called Yanjiao fault depression in this paper. The maximum Quaternary thickness of the graben is 300m. The West Xiadian Fault is the main controlling fault in the southern margin of the sag. The Xiadian Fault, which is opposite to the West Xiadian Fault in dips, controls the Dachang depression, which is a large-scale depression with a Quaternary thickness of more than 600m. The West Xiadian Fault is opposite to the Xiadian Fault, and there is a horst between the West Xiadian Fault and the Xiadian Fault. The width of the horst varies greatly, and the narrowest part is less than 1km. The West Xiadian Fault may form an echelon structure with Xiadian Fault in plane, and they are closely related in depth. According to the core histogram and logging curves of ten boreholes and eight effective dating data, the buried depth of the upper breakpoint of the concealed fault is about 12m, which dislocates the late Pleistocene strata. The effective dating result of this set of strata is(36.52±5.39)ka. There is no evidence of Holocene activity of the fault, but it is certain that the fault is an active fault in the late Pleistocene in Sanhe region. The vertical slip rate is about 0.075mm/a since late Pleistocene, and about 0.03mm/a since the late period of late Pleistocene. These slip rates are less than those of the Xiadian Fault in the same period. According to our study, the vertical slip rate of Xiadian Fault since late Pleistocene is about 0.25mm/a. Although the latest active age, the total movement amplitude since Quaternary and the sliding rate since late Pleistocene of West Xiadian Fault are less than those of Xiadian Fault, its movement characteristics is very similar to that of Xiadian Fault, and the two faults are close to each other in space, and closely related in deep structure. It can be inferred that the fault is probably a part of the seismogenic structure of the 1679 Sanhe-Pinggu M8 earthquake. In a broad sense, the Xiadian fault zone is likely to extend to the southwest along the West Xiadian Fault. Table and Figures | Reference | Related Articles | Metrics

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THE 2022 M6.8 LUDING EARTHQUAKE: A COMPLICATED EVENT BY FAULTING OF THE MOXI SEGMENT OF THE XIANSHUIHE FAULT ZONE LI Chuan-you, SUN Kai, MA Jun, LI Jun-jie, LIANG Ming-jian, FANG Li-hua SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1648-1666.   DOI: 10.3969/j.issn.0253-4967.2022.06.017 Abstract （787）   HTML （75）    PDF（pc） （16086KB）（344）       Knowledge map    Save The September 5, 2022, M6.8 Luding earthquake occurred along the southeastern segment of the Xianshuihe fault zone. Tectonics around the epicenter area is complicated and several faults had been recognized. Focal mechanisms of the main shock and inversions from earthquake data suggest that the earthquake occurred on a northwest-trending, steeply dipping strike-slip fault, which is consistent with the strike and slip of the Xianshuihe fault zone. We conducted a field investigation along the fault sections on both sides of the epicenter immediately after the earthquake. NW-trending fractures that were recognized as surface ruptures during the earthquake, and heavy landslides along the fault section between Ertaizi-Aiguocun village were observed during the field investigations. There are no surface ruptures developed along the fault sections north of the epicenter and south of Aiguocun village. Thus it can be concluded that there is a 15.5km-long surface rupture zone developed along the Moxi Fault(the section between Ertaizi and Aiguo village). The surface rupture zone trends northwest and shows a left-lateral strike slip, which is consistent with the strike and motion constrained by the focal mechanism. The coseismic displacements were measured to 20~30cm. Field observations, focal fault plane, distribution of the aftershocks, GNSS, and InSAR observation data suggest that the seismogenic structure associated with the M6.8 Luding earthquake is the Moxi Fault that belongs to the southeastern segment of the Xianshuihe fault zone. Slip along the segment south of the epicenter generated this earthquake, and also triggered slip along a northeast-trending fault and the northwestern section of the Moxi Fault in the epicenter. So, the M6.8 Luding earthquake is an event that is nucleated on the section south of the epicenter and then triggered an activity of the whole fault segment. Table and Figures | Reference | Related Articles | Metrics

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PROBING THE SUBSURFACE ELECTRIC STRUCTURE FOR CSELF NETWORK IN CAPITAL CIRCLE REGION DONG Ze-yi, TANG Ji, ZHAO Guo-ze, CHEN Xiao-bin, CUI Teng-fa, HAN Bing, JIANG Feng, WANG Li-feng SEISMOLOGY AND GEOLOGY    2022, 44 (3): 649-668.   DOI: 10.3969/j.issn.0253-4967.2022.03.006 Abstract （427）   HTML （25）    PDF（pc） （13890KB）（279）       Knowledge map    Save The first control source extremely low frequency(CSELF)electromagnetic observation network through the world, consisting of 30 fixed stations located in the Beijing captical circle region(15 staions)and the sourthern secton of the north-south earthquake belt(15 stations), China, has been established under the support of the wireless electromagnetic method(WEM)project, one of the national science and technology infrastructure construction projects during the 11th Five-year Plan period. As a subsystem of the WEM project, the CSELF network is mainly to study the relationship between elctromagnetic anomalies and mechanisms of earthquake, and further improve our ability to monitor and predict earthquakes by monitoring real-time dynamic changes in both electromagnetic fields and subsurface electric structure. Carrying out the detection of the underground background electric structure in the CSELF network area/station is an important part of this project and of great significance to play its role in the study of earthquake prediction and forecast. In this paper, we elaborate how to acquire the subsurface electric structure of the CSELF network in the Beijing captical circle region and make a simple explanation for the structure. Firstly, a short magnetotelluric(MT)profile, almostly perpendicular to the regional geological strike, was deployed at each station of the CSELF network in the capital circle region during the 2016 and a total of 60 broadband MT sites was collected using ADU -07e systems. Then, all the time series data were processed carefully using the robust method with remote reference technique to MT transfer functions. MT data quality was assessed using the D+algorithm. In general, data at most sites are of high quality as shown by the good consistency in the apparent resistivity and phase curves. Different impedance tensor decomposition methods including the phase tensor analysis, Groom and Bailey(GB)tensor decompositon, and statistical image method based on multi-site, multi-frequency tensor decompositon were used to analyze data dimensionality and directionality. For data inversion, on the one hand, one-dimensional(1-D)subsurface electrical resistivity structures at each station and MT site were derived from 1-D adaptive regularized MT inversion algorithm. On the other hand, we also imaged the 2-D electric structures along the short MT profile by the nonlinear conjugate gradients inversion algorithm at each station. Robustness of all 2-D structures along each short profile were verified by sensitivity tests. Although fixed stations and MT sites are limited and distributed unevenly, the 3-D inversion of 15 stations was also performed to produce a 3-D crustal electrical resistivity model for the entire network using the modular system for 3-D MT inverson: ModEM based on the nonlinear conjugate gradients algorithem. Intergrating 1-D, 2-D and 3-D inversion results, the resistivity structure beneath the CSELF network in captical circle region revealed some significant features: The crustal electrical structures are mainly characterized by high resistivity beneath the Yinshan-Yanshan orogenic belt in the northern margin of North China, the Taihangshan area in the middle, the Jiao-Liao block in the east, while the North China Plain and Shanxi depression areas have relatively lower resistivity in the crust; There are obvious electrical resistivity difference on both sides of the gravity gradient of Taihang Mountains and the Tanlu fault zone, which indicates they could be manifested as an electric structure boundary zone, respectively. Overall, the electric structure characteristics of the entire network area shows high correspondence with the regional geological structure and earthquake activity to some extent. In summary, implementing the detection of underground electrical resistivity structure in the CSELF network of the capital circle region will provide important foundations for the researches on the regional seismogenic environment, the generation mechanism of seismic electromagnetic anomaly signals, and earthquake prediction and forecast. Table and Figures | Reference | Related Articles | Metrics

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PRELIMINARY STUDY ON FAULTED LANDFORMS AND AGES OF RECENT STRONG EARTHQUAKE ACTIVITY ON THE KARAKORUM FAULT IN NGARI, TIBET XU Wei, LIU Zhi-cheng, WANG Ji, GAO Zhan-wu, YIN Jin-hui SEISMOLOGY AND GEOLOGY    2022, 44 (4): 925-943.   DOI: 10.3969/j.issn.0253-4967.2022.04.007 Abstract （505）   HTML （30）    PDF（pc） （14700KB）（272）       Knowledge map    Save The Karakoram Fault is located in the west of the Qinghai-Tibet Plateau and crosses Kashmir, Xinjiang and Tibet in China. It is a large normal dextral strike-slip fault in the middle of the Asian continent. As a boundary fault dividing the Qinghai-Tibet Plateau and the Pamir Plateau-Karakoram Mountains, the Karakoram Fault plays a role in accommodating the collision deformation between the Indian plate and the Eurasian plate and in the tectonic evolution of the western Qinghai-Tibet Plateau. The fault trace in Ngari area is clear and the faulted landforms are obvious, which show strong activity characteristics in late Quaternary. As a large active fault, only one earthquake of magnitude 7 has been recorded on the Karakoram Fault since the recorded history, namely, the Tashkurgan earthquake of 1895 at its north end. There are no records of strong earthquakes of magnitude≥7 along the rest of the fault, and no paleo-seismic research has been carried out. Ages of recent strong earthquake activity and earthquake recurrence intervals are not clear, which greatly limit the accuracy of seismic risk assessment. In this study, we investigated the fault geometry and faulted landforms in Ngari area, collected OSL samples of the faulted landforms and sag ponds in Zhaxigang, Menshi and Baga towns and preliminarily discussed the ages of recent strong earthquake activity. Study shows that the fault can be divided into three sections by Zhaxigang town and Suoduo village, and the structure and properties of each section are significantly different. In west Zhaxigang town section, the fault is dominated by dextral strike-slip with certain vertical movement, it is almost straight on the surface, with river terraces, alluvial-proluvial fans and water system faulted ranging from tens to hundreds of meters. In Zhaxigang town to Suoduo village section, the normal faulting is remarkable, the main fault constitutes the boundary fault between Ayilari Mountain and Gar Basin; fault facets and fault scarps are common along the fault line, there are also secondary faults with the same or opposite dip as the main fault developed near the piedmont basin. In east Suoduo village section, the main part of the fault is located at the south foot of Gangdise Mountain, and in addition to the piedmont fault, several approximately parallel faults are also developed on the southern alluvial-proluvial fans and moraine fans which are mainly dextrally faulted with certain vertical component. According to the analysis of the faulted landforms and dating of the OSL samples collected from the sag ponds and faulted landforms in the west of Zhaxigang town, the east of Menshi town and the east of Baga town, the ages of recent strong earthquake activity on the fault are analyzed as follows. In the west of Zhaxigang town, the age of recent strong earthquake activity of the fault is constrained to be close to 2.34kaBP according to the average OSL dating results of KKF-3 and KKF-4. In the east of Menshi town, the recent earthquake activity age of fault f2 is 4.67~3.01kaBP, but closer to 3.01kaBP according to the OSL dating results of KKF-11 of the youngest faulted geomorphic surface and average OSL dating results of KKF-6 and KKF-13 collected from sag ponds. In the area near Angwang village, Baga town, it is inferred that the recent strong earthquake activity age of the fault is close to 2.54kaBP according to the OSL dating results of KKF-2 collected from sag pond. If the faults of above three places are active at the same time, the age of recent strong earthquake activity of the fault is close to 2.63kaBP. The Karakorum Fault in Ngari area has obvious segment boundaries, and the activity of each segment and in its internal branch faults is most likely to be independent. The earthquake recurrence interval on the fault is estimated to be 2.8ka according to the slip rate and the amount of displacement. From the above analysis, it can be seen the time since the last strong earthquake activity of Karakorum Fault may have been very close to the interval of earthquake recurrence. If the fault is characterized by a quasi-periodic in-situ recurrence, the energy accumulation in the fault may have reached a very high degree and the risk of recurrence of strong earthquake events of the fault may be very high, so more attention should be paid and more detailed research on the paleo-earthquake events and recurrence intervals should be carried out as quickly as possible. Table and Figures | Reference | Related Articles | Metrics

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CHARACTERISTICS AND PROCESSING OF MAGNETOTELLURIC DATA UNDER STRONG ELECTROMAGNETIC INTERFERENCE ENVIRONMENT HAN Jing, ZHAN Yan, SUN Xiang-yu, ZHAO Guo-ze, LIU Xue-hua, BAO YU-xin, SUN Jian-bao, PENG Yuan-qian SEISMOLOGY AND GEOLOGY    2022, 44 (3): 736-752.   DOI: 10.3969/j.issn.0253-4967.2022.03.011 Abstract （461）   HTML （26）    PDF（pc） （15760KB）（252）       Knowledge map    Save With the development of national economic construction, high-speed railway, wind power stations, and photovoltaic power stations, large-scale high voltage power grids are widely distributed. Under these strong electromagnetic interference environments, obtaining high-quality magnetotelluric(MT)observation data is a practical problem. We carried out MT observation in Yinchuan, Yuncheng, Hebi, and Zhangjiakou in the past two years, and based on the data acquisition and processing results of around 500 MT stations in these four survey areas, 45 typical MT stations under strong electromagnetic interference environments are selected. Based on the nearest interference source, we sorted out these stations into seven kinds of strong electromagnetic interference environment. The seven kinds of strong electromagnetic interference environment are high-speed railway(0.5~1km), electrified railway(1.3~3.7km), wind power station(0.1~3.7km), photovoltaic power station(2~9km), large-scale high voltage power grids(0.06~0.4km), colliery(0.15~1km), and city(0.05~0.8km). The apparent resistivity curve obtained from processing of the typical MT station’s original data shows that the electromagnetic interference near the high-speed railway, electrified railway, and photovoltaic power station is mainly near-field interference. The mid-band frequency apparent resistivity curve of MT stations under near-field interferences rises along an angle of 45° while the impedance phase curve tends to 0. The electromagnetic interference of wind power generation facilities on MT data is relatively small. Large-scale high voltage power grids, colliery, and urban integrated electromagnetic interference are reflected in the apparent resistivity curve as discrete “outlier” with single or multiple frequency points. The curve does not have a stable shape at all. For the 45 typical MT stations listed in this paper under the strong electromagnetic interference environment, the data collection time covers two nights. The use of remote reference, non-robust processing, and fine spectrum selection for the full-time time series data improves MT data quality. The process of obtaining effective spectrum data and the results show that to get effective magnetotelluric data in a strong electromagnetic interference environment, the MT data observation time should include at least two nights(41h). Secondly, when the seven types of strong electromagnetic interference cannot be avoided, the MT stations should be placed at a distance of no less than 0.5km from high-speed railways, 1.3km from electrified railways, 2km from photovoltaic power stations, 0.2km from large-scale high voltage power grids, and 0.3km from colliery. It is also recommended that the distance of MT station shall be no less than 0.2km from electric wires, no less than 0.3km from transformers, and no less than 0.5km from thermal power stations in the comprehensive urban disturbance. The wind power stations have little effect on magnetotelluric data. Finally, a high-quality remote reference shall be used in the data processing. The use of this data can effectively suppress the influence of electromagnetic near-field interference by performing remote reference processing and estimating the spectrum data with the non-robust method. Table and Figures | Reference | Related Articles | Metrics

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A CENTENNIAL PUZZLE OF THE EVOLUTION OF THE YANGTZE RIVER: RETROSPECTION AND PROGRESSES GUO Ru-jun, WEI Chuan-yi, LI Chang-an, ZHANG Yu-fen, LI Ya-wei, SUN Xi-lin, ZHANG Zeng-jie, LENG Yong-hui, SU Jian-chao, LI Guo-nai, LÜ Ling-yun, CHEN Xu, DING Zhi-qiang SEISMOLOGY AND GEOLOGY    2023, 45 (1): 1-28.   DOI: 10.3969/j.issn.0253-4967.2023.01.001 Abstract （430）   HTML （64）    PDF（pc） （9173KB）（247）       Knowledge map    Save The evolution history of the great rivers is one of the most important subjects in earth science, especially, the capture events and changes of great rivers which originate from the inner area of the Qinghai-Tibetan plateau and flow into the ocean are hot problems for geomorphology and geology. The Yangtze River is a representative river link with the Qinghai-Tibetan plateau and the Pacific Ocean, formation of the Yangtze River is considered an important mark ofthe Chinese landscape formation and the establishment of the modern geomorphic pattern of the East Asia. The evolution of the Yangtze River is closely linked to the uplift of the Qinghai-Tibetan plateau and the birth of the margin seas and monsoon evolution. In this study, we concluded the main debates on the evolution of the Yangtze River for more than one century, and the progresses of provenance analysis applied to the continental and sea basins of the Yangtze River in the past two decades. We collected the provenance analysis results from typical sedimentary depositions in the Yangtze River catchment, including the Xigeda Formation in the Panzhihua-Xichang area of the upper reaches, Cenozoic sedimentary of the Jianchuan Basin which is near the First Bend of Shigu, Gravel Layers in the middle and lower reaches, borehole sediment of the Jianghan Basin and Yangtze River Delta, and sediment of the marginal sea basins(Yinggehai Basin, Taiwan Island). We conclude that: 1)the debates on the evolution of the Yangtze River are still focused on two questions: when the Three Gorges was formed and whether south flowed off the palaeo-Jinsha River in the First Bend of the Shigu, but the debates have extended to the palaeo-drainage model in East Asia during the Cenozoic period, geomorphic formation history and exhumation-deposition process of the SE Tibet, high elevation-low relief surface formation in the SE margin of the Tibet and many important issues. 2)There is no consensus regarding the formation time and process of the Three Gorges and the First Bend, the formation time, process, and mechanism of the Yangtze River are still vigorously debated. There are mainly two views on the Miocene and early-middle Pleistocene for the formation time of the Yangtze River and mainly three paleo models of the upper Yangtze, south flow, east flow, and southeast flow. The provenance of gravel layers in the middle and lower reaches of the Yangtze River and boreholes sediment in the Jianghan Basin have complex source regions. Because of the extreme stability and multiple recycle of the detrital zircons, it is difficult to distinguish the provenance signals of the upper reaches of the Yangtze River effectively from the modern and Cenozoic sediment in basins based on the detrital zircon U-Pb age, whether the “Yangtze Gravel at Nanjin” represents the age of the Yangtze River is still strongly debated. There is still no agreement on the initial signal of the sediment of the upper Yangtze River from the boreholes record in the Jianghan Basin and the Yangtze River Delta. The boreholes deposition age is also controversial. The provenance implications of the Cenozoic sediment of the Jianchuan Basin and the Xigeda Formation for the south flow(east flow)of the Jinsha River are widely debated. The marginal sea sediment provenance signals that constrain the evolution model between the Yangtze and the Red River are also controversial. 3)There is a big difference between the drainage catchment of the paleo-Yangtze and modern Yangtze, in the provenance analysis of the sedimentary basins of the Yangtze River, suggesting constrain provenance area by multi-mineral and multi-index and strengthen the comparison between the continental and marginal sea basins. The evolution history of the Yangtze River will be reconstructed more comprehensively from the perspective of geomorphology, tectonic evolution, sedimentary paleogeography and climate change. Table and Figures | Reference | Related Articles | Metrics

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PALEOSEISMOLOGIC STUDY ON THE YUEXI FAULT IN THE MIDSECTION OF THE DALIANGSHAN FAULT ZONE SINCE THE LATE QUATERNARY LIU Qing, LIU Shao, ZHANG Shi-min SEISMOLOGY AND GEOLOGY    2023, 45 (2): 321-337.   DOI: 10.3969/j.issn.0253-4967.2023.02.002 Abstract （264）   HTML （46）    PDF（pc） （15181KB）（246）       Knowledge map    Save The Xianshuihe-Xiaojiang fault system(XXFS)is a strongly active left-lateral strike-slip fault zone on the eastern edge of the Qinghai-Tibetan plateau. It controls the eastern boundary of the Sichuan-Yunnan block, Which is one of the most active tectonic zones in the north-south seismic belts. There have been 36 destructive earthquakes since 1327AD. The historical strong earthquakes in the middle section of the XXFS fault system are mainly distributed along Anning River faults and Zemu River faults, such as M7.0 in 814AD, M71/2 in 1536AD, M63/4 in 1732AD, M71/2 in 1850AD and M63/4 earthquakes in 1952AD. However, as an important part of the middle of XXFS, the Daliangshan fault zone only recorded a magnitude of M51/2 in 1480AD, and there was a lack of earthquake records above a magnitude of 6 which may be due to the quiet period of earthquakes, or the location of remote mountainous areas where historical records are missing. The paleoseismic study revealed that there were surface rupture events along the Butuo and Jiaojihe faults in the southern section of the Daliangshan fault zone in 970-1510AD and 1310-1660AD respectively, with a magnitude of not less than 6.5; Along the Puxiong fault in the middle section of the Daliangshan fault zone, there was a surface rupture event in 927-1360AD, with a magnitude of not less than 7.0. However, there are no corresponding historical records of the earthquakes in these three historical periods, indicating that strong historic earthquakes in the Daliangshan fault zone may be missing. The Yuexi fault is the only branch fault in the Daliangshan fault zone dominated by thrust slip. The fault spreads in an arc shape, with a total length of about 50km, and controls the quaternary basins such as Zhenxi, Xinmin, and Yuexi. The topographic height difference between the fault’s two sides is about 2 000m. The middle section of the fault is the eastern boundary fault of the Yuexi Basin, which cuts through the piedmont alluvial fan, forming fault scarps several meters to tens of meters high. Together with the Puxiong fault on the east side, which is dominated by left laterally slipping, a positive flower-type structure is formed in the middle section of the Daliangshan fault zone. There are previous discoveries about fault scarps of the Yuexi fault on the piedmont alluvial fans, but no paleoseismic research has been reported up to now. On the basis of remote sensing interpretation and field geological and geomorphological survey of the Yuexi fault, a big trench was excavated across the 12m-high fault scarp on the late quaternary alluvial fan in the Yuexi Basin, which revealed four paleoseismic events since the late quaternary and the coseismic vertical slip of the last one is ~1.2m. Based on trench analysis, 14 stratigraphic units are defined from which carbon samples are acquired for geochronological analysis. Through radioactive carbon dating and correction of the dating data by the OxCal software, and OxCal model building to limit the age of paleoearthquake events, the ages of the four events were 25260-23880BC, 23930-23500BC, 20980-1400BC, and 270-1500AD. According to historical records, a destructive earthquake occurred in Yuexi County on September 13, 1480AD, which triggered landslides, 7 earthquakes on that day, and more than 20 aftershocks as of the 27th, with a tremor range of 150km. We consider that the latest event should be the Yuexi earthquake in 1480AD according to the historical records of earthquake damages. Based on the paleoearthquake research, this event very likely led to a coseismic rupture of the Yuexi and the Puxiong faults. According to the empirical scaling laws between magnitude and rupture length, the magnitude of the surface ruptured paleoearthquake is estimated to be more than M7.0. The results provide basic data for evaluating seismic activity and analyzing seismic risk in this area. Table and Figures | Reference | Related Articles | Metrics

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FINE CHARACTERISTICS OF EARTHQUAKE SURFACE RUPTURE ZONE BASED ON HIGH-RESOLUTION REMOTE SENSING IMAGE: A CASE STUDY OF LITANG FAULT YOU Zi-cheng, BI Hai-yun, ZHENG Wen-jun, PENG Hui, LIANG Shu-min, DUAN Lei, QIN Yi-gen SEISMOLOGY AND GEOLOGY    2023, 45 (5): 1057-1073.   DOI: 10.3969/j.issn.0253-4967.2023.05.002 Abstract （236）   HTML （35）    PDF（pc） （10517KB）（246）       Knowledge map    Save Strong earthquakes(magnitude>6.5)typically cause coseismic surface ruptures of several kilometers or even hundreds of kilometers long on the surface. Coseismic surface rupture is the most intuitive geomorphic representation of an earthquake on the surface, and its geometry and distribution characteristics provide important information about the fault activity. Field investigation is the most basic means for research on coseismic surface fractures, but for areas that are hard to access or have harsh climatic environments, field investigation is often greatly limited. In recent years, the increasing abundance of high-resolution remote sensing images and the rapid development of photogrammetry methods can help us quickly obtain high-resolution topographic and geomorphic data of the study area, to better identify the fine geometry of the earthquake surface rupture zone and measure the offsets of geomorphic markers along the fault. The Litang Fault is a sinistral strike-slip fault located within the Sichuan-Yunnan rhombic block on the eastern edge of the Qinghai-Tibetan plateau. Several historical earthquake events have occurred on this fault, such as the 1890 and 1948 earthquakes, and clear seismic surface ruptures still exist along the fault so far. Previous studies have conducted a series of works on the coseismic surface rupture of this fault, but most of these works were based on field investigations or relatively low-resolution remote sensing images, and there is still a lack of fine research on the coseismic surface rupture of the fault. In this paper, the coseismic surface rupture of the 1890 earthquake which occurred on the Litang Fault was selected as the study object. To obtain high-resolution topographic data of this fault, the WorldView satellite stereo images were used to generate a 0.5-m-resolution orthophoto and a 1-m-resolution Digital Elevation Model(DEM)of the Litang fault based on the photogrammetry method. With the high-resolution topographic data, the fine geometry of the 1890 earthquake surface rupture zone was mapped in detail. The mapping results show that the total length of the surface rupture is about 27km, with an overall strike of N40°W. The rupture is mainly characterized by sinistral strike-slip motion, with a certain degree of dip-slip component in local areas. Except for the interval of approximately 6km with no surface rupture at the Wuliang River floodplain in the Litang Basin, the surface ruptures are relatively continuous at other locations. In addition, various rupture styles have been identified along the fault, including en echelon tension cracks, mole tracks, sag ponds, fault scarps, and displaced gullies. Furthermore, the sinistral offsets of 90 groups of linear geomorphic markers such as gullies and ridges were measured along the fault, which range from 1m to 82.4m. We further estimated the Cumulative Offset Probability Distribution(COPD)of the offsets located on the terrace I of the Wuliang River, which are all in the range of 0-9m. The COPD plot displays four distinct peaks at 1.3m, 2.4m, 4.3m, and6.1m, respectively. Previous studies have reported that the terrace I of Wuliang River formed at about(4 620±40)a BP. Thus, it can be indicated that the Litang fault may have experienced at least four strong earthquake events since(4 620±40)a BP, and the smallest peak of 1.3m may represent the coseismic displacement of the most recent 1890 earthquake. The rupture length of the latest 1890 earthquake was about 27km, and the coseismic sinistral offset was about 1.3m, yielding an estimated moment magnitude of MW6.8-7.1. The coseismic offset of the other three earthquakes was about 1.8m, 1.9m, and 1.1m from old to new, respectively, yielding a magnitude estimate of MW7.3, MW7.3, and MW7.0, with a size comparable to the 1890 earthquake. The research results fully demonstrate the potential of high-resolution remote sensing images in the study of fine characteristics of earthquake surface rupture. Table and Figures | Reference | Related Articles | Metrics

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AMBIENT NOISE EIKONAL TOMOGRAPHY BASED ON MUTI-CHANNEL CROSS-CORRELATION IN THE NORTHEASTERN MARGIN OF THE TIBETAN PLATEAU MA Xiao-jun, WU Qing-ju, PAN Jia-tie, ZHONG Shi-jun, XU Hui SEISMOLOGY AND GEOLOGY    2022, 44 (3): 604-624.   DOI: 10.3969/j.issn.0253-4967.2022.03.004 Abstract （403）   HTML （41）    PDF（pc） （13190KB）（244）       Knowledge map    Save The traditional surface wave tomography method is a ray-theoretic travel-time tomography based on the high-frequency approximation, and adopts the regularization method with model smoothing parameters, which is likely to produce false anomalies. The current eikonal tomography is a geometrical ray theoretic method that can obtain the travel time gradient of the wave field by tracking the propagation of the wave front, and then get the slowness vector of wave field gradient. This method has the advantages of high efficiency and high resolution. But both surface wave travel-time tomography and traditional eikonal tomography need to extract dispersion curve. For example, the extraction of dispersion curve with auto frequency-time analysis method usually requires a manual extraction again, which may increase systematic error or human error. The multichannel cross-correlation surface wave eikonal tomography for earthquakes developed in recent years does not need to extract the dispersion curve, but automatically measures the relative phase delay between nearby stations based on waveform cross-correlations by using the far field condition of wave equation, and then inverts the two-dimensional surface wave phase velocity distribution with eikonal tomography method. This method can suppress the random incoherent noise and reduce bias caused by strong multipath scattering. In this paper, we collected the one-year three-channel continuous waveform data from 676 temporary stations under the project China Array II and calculated the surface wave empirical Green’s function of ambient noise through noise cross-correlation from January to December 2015. The multichannel cross-correlation surface wave eikonal tomography was firstly applied to ambient noise tomography. The first step was to calculate the relative phase delay using the multi-channel cross-correlation, and at the second step, we inverted the Rayleigh wave apparent phase velocity at 8~40s periods based on eikonal equation for the whole study area, with the high resolution of about 40km in the major regions. At last, we compared our results with other results and discussed the tectonic deformation and dynamic process of the study area. The results are as follows: (1)In contrast to traditional eikonal tomography method in which the dispersion has to be extracted based on frequency analysis, our results can reduce the bias resulting from multi-path scattering wave and low signal-to-noise ratio, and improve the stability of inversion results. Moreover, our results of long-period surface waves have higher accuracy and stability because our method reduces short-wavelength heterogeneity. (2)There are obvious low-velocity anomalies in the upper crust of Hetao-Jilantai Basin at 18s period, and a weak low-velocity zone in the lower crust and upper mantle, which is associated with the upwelling of hot asthenosphere mantle materials in the “big mantle wedge”. (3)A weak layer with low S-wave velocity exists in the middle and lower crust of the northeastern Songpan-Garzê block and the western Qilian orogenic belt. Receiver function results indicate that there is high Poisson’s ratio(0.28)and low P wave velocity(less than 6.3km/s)in the northeastern Songpan-Garzê block, which may suggest partial melting in the middle and lower crust of the northeastern Songpan-Garzê block; The radial anisotropy from ambient noise tomography in the western Qilian orogenic belt shows negative radial anisotropy characteristics, which may be associated with the crustal shortening, thickening and coupling under the compression from the north and south blocks. Table and Figures | Reference | Related Articles | Metrics

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APPLICATIONS AND ADVANCES FOR THE COSEISMIC DEFORMA-TION OBSERVATIONS, EARTHQUAKE EMERGENCY RESPONSE AND SEISMOGENIC STRUCTURE INVESTIGATION USING INSAR ZHAO De-zheng, QU Chun-yan, ZHANG Gui-fang, GONG Wen-yu, SHAN Xin-jian, ZHU Chuan-hua, ZHANG Guo-hong, SONG Xiao-gang SEISMOLOGY AND GEOLOGY    2023, 45 (2): 570-592.   DOI: 10.3969/j.issn.0253-4967.2023.02.016 Abstract （331）   HTML （22）    PDF（pc） （7303KB）（239）       Knowledge map    Save With the recent development of geodetic observation theory, the increasing satellite platforms and the progress of related technology, InSAR is emerging as a new data source and useful tool for remotely-based geodetic observations. More importantly, InSAR observations play an increasingly irreplaceable role in the field of coseismic deformation observations, earthquake emergency responses, earthquake hazard evaluation and seismogenic structure research. Particularly, InSAR is the most commonly used tool in coseismic deformation measurements on the Qinghai-Tibetan plateau or other global seismic zones, where GPS data are sparse or inaccessible in some cases. Specifically, InSAR measurements help us to respond in time after disastrous earthquakes and provide valuable information associated with how the surface of the crust deforms due to large earthquakes. In the area of scientific research, InSAR provides products of surface deformation observations and serves as model constraints kinematically or dynamically in identifying the buried faults, studying the characteristics of seismogenic faults, obtaining three-dimensional displacements, and investigating the relationship between earthquakes and tectonic structures. InSAR observations and its deformation products have the technical advantages of large spatial scale, high precision and in-time, compared to other geodetic measurements. Consequently, InSAR has the ability to provide scientific and technological support for earthquake emergency observations, and meeting the practical needs of earthquake disaster reduction on the Qinghai-Tibetan plateau. In this review, we mostly limit our focus to the application of InSAR technology in earthquake cycle deformation monitoring in different structural settings on the Qinghai-Tibetan plateau. We also summarize the InSAR-based studies on fault kinematics and seismogenic structures related to some noted earthquakes on the Qinghai-Tibetan plateau. We highlight how the applications of InSAR data can greatly promote earthquake science and can be used as routine observations in some important areas. Then proceed to discuss the cutting-edge development trend and some new challenges of InSAR technology, which are frequently discussed and investigated, but not well resolved, in recent applications. The endeavors in increasing the precision of small-magnitude deformation measurements and expanding the InSAR data volumes can make the scientific objectives of earthquake disaster reduction on the Qinghai-Tibetan plateau and its surrounding areas feasible and reliable. To better understand how InSAR observations have changed the way we study earthquakes, we summarize the development, commercialization, insights, and existing challenges associated with InSAR coseismic deformation measurements and application in recent two decades. Table and Figures | Reference | Related Articles | Metrics

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RESEARCH PROGRESS AND PROSPECT OF SEISMIC FLUID GEOCHEMISTRY IN SHORT-IMMINENT EARTHQUAKE PREDICTION LI Ying, FANG Zhen, ZHANG Chen-lei, LI Ji-ye, BAO Zhi-cheng, ZHANG Xiang, LIU Zhao-fei, ZHOU Xiao-cheng, CHEN Zhi, DU Jian-guo SEISMOLOGY AND GEOLOGY    2023, 45 (3): 593-621.   DOI: 10.3969/j.issn.0253-4967.2023.03.001 Abstract （273）   HTML （40）    PDF（pc） （2594KB）（235）       Knowledge map    Save Establishing the method of short-imminent earthquake prediction is the most effective way to reduce losses caused by earthquakes and is also an important scientific issue. In the 1960s and 1970s, research on earthquake prediction was carried out successively in China and other countries in the world, and after over 50 years of development, abundant precursor observation data and earthquake cases have been accumulated, and significant progress has been made in the research of formation mechanisms of precursor anomalies and prediction methods. Fluid is the most active component in the earth’s interior, and the fluids in various layers of the earth often carry characteristic geochemical information. The composition and variation of seismic fluid geochemistry are sensitive to changes of underground physical and chemical conditions, making them powerful indicators of seismic and tectonic activities. The formation mechanisms of fluid geochemical precursor anomalies mainly include liquid mixing, water-rock reaction, deep magma upwelling, seismic wave vibration, pore compression and pressure solubility mechanism. The fluid chemical anomalies associated with earthquakes can be attributed to the migration process of liquid mixing and the water-rock reaction mechanism caused by crustal stress changes. This paper systematically summarizes the empirical formulas on the duration of anomaly, earthquake magnitude and epicentral distance, as well as the seismic fluid geochemical models and methods for short-imminent prediction established both domestically and internationally. In addition, four types of seismic fluid geochemical techniques and methods currently used in earthquake situation consultation in China are described. Nine of the most widely used prediction methods are selected to inspect the twenty-seven cases of earthquakes containing water radon or gas radon anomalies in the Earthquake Cases of China from 1997 to 2020. Generally, these methods all show strong applicability. However, empirical formulas based on different regions of the world selected to inspect the above cases generally show weak applicability. It indicates that current earthquake prediction models or methods are only representative to a certain extent, and there are still great difficulties in practical application, which also directly affects the prediction efficiency of the fluid geochemical models applied to the judgment of earthquake three elements. Combined with our previous results, the paper puts forward the applicable theory for the precursor mechanism-based short-imminent prediction by seismic fluid geochemistry, that is, acquiring the dynamic change characteristics of the geochemical field based on the spatio-temporal dense and multi-item observation network, establishing a deep-shallow coupling anomaly genetic model based on the material cyclic reaction, and determining the temporal and spatial relationship between the evolution of regional fluid geochemical field and fluid geochemical changes at each measuring point in the fault zone. The construction of the geochemical subsystem of China Seismic Experimental Site provides a platform for capturing the short-imminent earthquake anomalies and constructing effective fluid geochemical anomaly mechanisms and models. The causes and abnormal mechanism of fluid geochemistry can be revealed and the seismic fluid geochemical short-imminent prediction method can be established in the light of the principle of seeking the source by field and combining the field and source. Table and Figures | Reference | Related Articles | Metrics

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A DISCUSSION ON THE RELATIONSHIP BETWEEN THE SUR-FACE RUPTURE ZONE IN FRONT OF THE AMUNIKESHAN MOUNTAIN AND THE 1962 M6.8 EARTHQUAKE YAO Sheng-hai, GAI Hai-long, YIN Xiang, LIU Wei, ZHANG Jia-qing, YUAN Jian-xin SEISMOLOGY AND GEOLOGY    2022, 44 (4): 976-991.   DOI: 10.3969/j.issn.0253-4967.2022.04.010 Abstract （347）   HTML （26）    PDF（pc） （15635KB）（220）       Knowledge map    Save The investigation of seismogenic structure of historical strong earthquakes and the research on the genetic link between earthquakes and active faults are a basic seismogeologic work. In particular, the investigation of seismic surface rupture zones and the study of seismogenic structures are extremely important for understanding the characteristics of their tectonic activities. The determination of the macro-epicenter provides important evidence for the site selection for post-disaster reconstruction and avoidance. Due to the diversity of the rupture process in the focal area, the macro-epicenter and the micro-epicenter may not be identical. As the magnitude increases, the larger the focal area of an earthquake is, the more significant the gap between the macro-epicenter and the micro-epicenter will be. The northern margin of the Qaidam Basin is an area with frequent earthquakes, where many earthquakes with magnitude above 6.0 occurred in the history. In the early and late 1990s, small earthquake swarms with long duration and high frequency occurred in this area, which caused considerable losses to the local industry. Since the Delingha earthquake of magnitude 6.6 in 2003, two earthquakes with magnitude 6.3 and 6.4 occurred in the northern margin of the Qaidam Basin in 2008 and 2009, which aroused great attention of researchers. A new research focus has emerged on this area, and many scholars conducted in-depth research on the faults of the northern margin of the Qaidam Basin. The author conducted a preliminary remote sensing interpretation of the Amunikeshan Mountain segment of the northern margin of the Qaidam Basin and found that there is a very straight linear feature in the image of the Amunikeshan mountain front. On the basis of remote sensing interpretation, a related study was carried out on the Amunikeshan segment of the northern margin fault of the Qaidam Basin, which was considered to be a Holocene active fault. Since the late Holocene, the horizontal movement rate of the fault is 2.50~2.75mm/a, and the vertical movement rate is(0.43±0.02)mm/a. A 30km-long earthquake surface rupture zone was found in front of Mount Amunikeshan. It is preliminarily believed that the rupture might be caused by a strong historical earthquake. According to the catalogue of historical strong earthquakes and local chronicles, there were earthquakes of magnitude 6.8 and 6.3 occurring in this area on May 21, 1962 and January 19, 1977, respectively. There has been no detailed research report on these two earthquakes. Through on-the-spot geological investigation, it is found that there are fault scarps, fault grooves, seismic bulges and ridges, twisted water system and other landforms developed along the line, forming a surface rupture zone with a strike of N30°-40°W, a coseismic displacement of 2.3m, and a length of about 22km. Through trenching and excavation, the trench section reveals several faults, indicating the characteristic of multi-stage activity. In the section, the faults ruptured to the surface, and the late Quaternary activity is obvious. Combining surface relics, geological dating, and micro-geomorphic measurements, it is determined that the nature of the fault is mainly strike-slip with thrust. The investigation has found many seismic geological disasters, such as landslides, rockfalls and ground fissures along the fault, which are judged to be generated in recent decades or centuries. Based on the empirical statistical relationship between magnitude and surface rupture, and the empirical relationship between strike-slip fault and rupture length, the average magnitude required for producing a 22km-long earthquake surface rupture is 6.79, and the average magnitude for producing a 2.3m coseismic displacement is 7.03. In combination with the surface rupture, trench profile, geological dating, seismic geological disasters, empirical formula calculation, historical earthquake catalogue, local chronicles and other documents, it is considered that the rupture zone is most likely produced by the North Huobuxun Lake M6.8 earthquake on May 21, 1962, and its seismogenic fault is the Amunikeshan Mountain segment of the northern margin fault of the Qaidam Basin. Since the study area has no permanent residents or buildings(structures), which are taken as the basis for inquiring and investigating the earthquake intensity, we are unable to draw the earthquake intensity map. Table and Figures | Reference | Related Articles | Metrics

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THE LATE QUATERNARY ACTIVITY CHARACTERISTICS AND SLIP RATE OF BATANG FAULT IN SE TIBETAN PLATEAU HUANG Wei-liang, ZHANG Jia-le, XIANG Wen, YANG Qian-hao SEISMOLOGY AND GEOLOGY    2023, 45 (6): 1265-1285.   DOI: 10.3969/j.issn.0253-4967.2023.06.002 Abstract （132）   HTML （25）    PDF（pc） （17828KB）（195）       Knowledge map    Save The southeastern margin of the Tibetan plateau is one of the most intensely deformed regions in the continental crust. A series of active faults with varying lengths and mechanical properties have segmented the lithosphere into multiple active blocks, with the Sichuan-Yunnan block being one of the most tectonically active regions. Its eastern boundary is characterized by secondary fault zones such as the Xianshuihe-Anninghe-Zemuhe, Xiaojiang, and Daliangshan fault zone, forming a narrow and continuous strike-slip deformation zone with a total length exceeding 1 100km. The western boundary of the Sichuan-Yunnan Block is mainly composed of the Jinsha River and the Red River fault zone, with the Jinsha River fault zone consisting of more than 20 roughly parallel secondary faults, forming a complex fault zone with 30~200km width. Despite recent GNSS network observation revealing the current tectonic deformation rates in this region, there is still a lack of research on the deformation characteristics and rates of individual active faults. This limitation makes it difficult in the assessment and understanding of seismic hazards in the area, restricting the scientific understanding of the current deformation mode in the southeastern margin of the Tibetan plateau. The Batang Fault, located within the Jinsha River fault zone at the western boundary of the Sichuan-Yunnan block, is a NE-trending main fault that obliquely cuts across the Jinsha River Fault, dividing later into northern and central segments. Presently, the Batang Fault is characterized by dominant right-lateral strike-slip motion. The deformation characteristics and rates of this fault since the Late Quaternary are crucial for understanding the spatial distribution of strong earthquakes and deformation patterns in the Sichuan-Yunnan block. The Batang Fault has a total length of 115km and is a Holocene right-lateral strike-slip active fault. The fault extends along the margins of bedrock mountains on both sides of the Maqu river and Jinsha River valleys, trending NNE or NWW to SEE, with a steep dip. The fault exhibits linear distribution of topographic features such as slopes, ridges, triangular facets, and fault scarps, essentially controlling the boundaries of bedrock mountains. In view from the geomorphology, the Batang Fault appears continuous and straight without distinct segmentation, except for localized small-scale step-like features. The Batang Fault has preserved abundant Late Quaternary activity evidence in two areas, Huangcaoping village and Batang county. This study utilized unmanned aerial vehicle photogrammetry to establish sub-meter digital terrain data for Huangcaoping and Batang site, accurately measuring displaced features such as alluvial fans and gullies affected by faulting. In Huangcaoping site, the fault has cut through multiple mountain-front alluvial fans, causing varying degrees of horizontal displacement in features such as gullies and the margin of the alluvial fans. This provided a scale for quantifying fault displacement. In Huangcaoping, five large-angle gullies intersect with the fault, one of which is a large gully developed in the bedrock mountain area. The gully has a deep incision, a narrow valley, and a rapid downstream turn to the right after exiting the mountain. The left bank of the gully preserves two geomorphic surfaces, Qo(older)and Qi(younger)surface, with the fault cutting across both surfaces, forming linear steep terrain. The measured total right-lateral offset of this gully since exiting the bedrock mountain area is(46±9)m. To constrain the activity rate of the Batang Fault at this location, we used cosmogenic nuclide single clast dating to determine the exposure age of the oldest geomorphic surface, Qo, as(12.5±0.5)ka. Considering that the formation of the river predates the Qo geomorphic surface, the age-constrained slip rate of the fault at this location is considered a maximum value, estimated at(3.6±0.8)mm/a. At Batang county, the Batang Fault has preserved clear faulted topography when cutting through the Moqu alluvial fan. The southern edge of the Moqu alluvial fan has been displaced by the fault, providing a well-preserved geomorphic marker for determining the strike-slip displacement of the fault. The Batang Fault, when intersecting the steep edge of the Moqu River alluvial fan, caused an obvious right-lateral offset, determined by comparing the consistent morphology of the steep edge on both sides of the fault. The right-lateral strike-slip displacement along the southern edge of the alluvial fan is measured at (40±5)m. The cosmogenic nuclide depth profile dating was used to determine the age of the faulted alluvial fan. From a vertical profile excavated along a man-made road on the edge of the alluvial fan, four mixed samples of small pebbles were collected from bottom to top. The calculated exposure ages of the debris flow alluvial fan are (15.2+3.2/-5.4)ka (without consideration of erosion)and (16.4+3.9/-5.6)ka (with consideration of erosion). Combining the fault displacement along the southern edge of the alluvial fan and the cosmogenic nuclide depth profile ages, the slip rate of the Batang Fault at this location is estimated to be of(2.6±0.6)mm/a (without erosion)or(2.4±0.8)mm/a (considering erosion). We believe that the age results with consideration of erosion effects is closer to the true values, thus we take 2.4mm/a as the activity rate of the Batang Fault at this location. The two slip rate values of the Batang Fault obtained in the Huangcaoping and Batang county sites are similar, indicating a right-lateral strike-slip rate of 2~4mm/a since the Late Quaternary. This rate accounts for 50%~80% of the present GPS observation shear deformation across the western boundary of the Sichuan-Yunnan block, indicating that the Batang Fault is a major deformation absorption zone in the Jinsha River fault zone. However, this rate is lower than the predicted~10mm/a using block models. The discrepancy may be due to the different understanding of the deformation mode at the western boundary of the Sichuan-Yunnan Block. In the block model, block sliding mainly relies on the primary boundary fault to regulate, but the long-term and lower geological activity rate of the Batang Fault obtained in this study does not match the assumption of a higher activity rate for the boundary fault in this model. The continuous and diffuse deformation characteristics of crustal deformation in the southeastern margin of the Tibet plateau may corroborate the lower activity rate of the Batang Fault obtained in this study. Table and Figures | Reference | Related Articles | Metrics

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NEW ACTIVITY PHENOMENA REVEALED BY TRENCH ON THE NORTH SIDE OF NÜSHAN LAKE IN THE TANLU FAULT ZONE AND DISCUSSION ZHAO Peng, LI Jun-hui, TAO Yue-chao, SHU Peng, FANG Zhen SEISMOLOGY AND GEOLOGY    2023, 45 (2): 338-354.   DOI: 10.3969/j.issn.0253-4967.2023.02.003 Abstract （179）   HTML （19）    PDF（pc） （13253KB）（194）       Knowledge map    Save The Tan-Lu fault zone is a huge seismic-tectonic belt in the eastern China. It can be generally divided into three segments: the north, the middle, and the south segment. Among them, recent activity of the middle segment has been most thoroughly studied. The junction section between Jiangsu and Anhui Province is located in the transition zone between the middle and the south segment of the fault zone. Due to the complex tectonic structure, unevenly distributed Quaternary deposits and severely transformed surface landscape, it is difficult to study the recent Quaternary activity of the fault. Research in recent years have shown that the faults in the Fushan and Ziyang areas to the south of the Huaihe River were active during late Pleistocene-early Holocene, and their activities were characterized by thrusting, normal faulting, tension and twisting. How is the fault activity extending southwards to Nüshan Lake and whether the late Quaternary activity occurred at Nüshan Lake are issues worthy of attention. Geomorphology of the study area is characterized by slope plains and uplands. The uplands mostly extend in near north-south direction and are obviously controlled by the faults. In the remote sensing satellite images, linearity features of the fault from Huaihe River to Nüshan Lake are distinct. Field investigations confirmed that in the farmland to the east of Liugudui Village, north of Nüshan Lake, there are scarps extending in NNE direction and distributing intermittently due to faulting. In this study, we chose relatively clear scarps and excavated trenches across the fault. The trench revealed abundant faulting phenomena. The trench wall revealed a fault deformation zone as wide as 2~4 meters, consisting of 3 fault branches. Among them, faults f1 and f3 are the boundary faults while fault f2 is developed within the deformation zone. The latest activity of fault f3 on the west side has ruptured the overlying horizon of late Pleistocene strata, and the rupture extended upwards to the surface. OSL dating samples were collected in the uppermost layer of the faulted horizons. Dating results show that the fault has been active at least in late Pleistocene. The scratches and steps developed on the fault plane indicate that the fault has experienced thrusting and dextral faulting. The deformation zone appears dark brown, which is conspicuously different from the horizons on both sides. Materials in the fault zone are compacted, crumpled and deformed, and the alignment direction is consistent with the fault. The deformation zone contains gravels and calcium tuberculosis of different sizes. Two brownish-yellow clay masses in irregular shape are deposited near the upper part of the fault plane. Among them, the clay mass tk1 on the south wall of the trench is quite clear, with the upper part connected with f1 and the middle part obliquely cut by f2. OSL dating samples were collected from clay masses from two trench walls. The dating results are consistent with the late Pleistocene horizons, indicating that the brownish-yellow clay masses were involved in the fault zone when faulting occurred in the middle-late Pleistocene, and the faulting event occurred roughly between(50.92±4.65)kaBP and(27.12±2.26)kaBP. Our research shows that late Quaternary activity of the most active fault of the eastern branch of the Tanlu fault zone extended southwards to Nüshan Lake in Mingguang, but intensity of the fault activity has weakened. The segment from Sihong in Jiangsu Province to Mingguang in Anhui Province is the structural node between the middle segment and the southern segment of the Tanlu fault zone. Trench exposures in Wangqian, Sunpaifang, Dahongshan in Sihong and Santang, Ziyang, Zhuliu in Mingguang and other places revealed a variety of faulting phenomena such as wedges, wedge-shaped mass, normal faulting, negative flower-shaped structure, clay mass, etc. These show that faults that were dominantly thrusting led to the local and abundant phenomena near surface in this region. The reasons for these different phenomena may be related to the influence of regional complex stresses and their changes on large-scale fault systems at different time and spaces scales. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE DEEP STRUCTURAL CHARACTERISTIC OF MAIN ACTIVE FAULTS IN HENAN PROVINCE AND ITS ADJACENT AREAS XU Zhi-ping, ZHANG Yang, YANG Li-pu, XU Shun-qiang, JIANG Lei, TANG Lin, LIN Ji-yan SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1521-1538.   DOI: 10.3969/j.issn.0253-4967.2022.06.010 Abstract （348）   HTML （22）    PDF（pc） （7110KB）（194）       Knowledge map    Save There are many first-order intersecting tectonic units and different strike faults developed widely in Henan Province, and many historical earthquakes with magnitude 6 and above occurred, which have brought great losses to people’s lives and property. In order to effectively reduce the risk of earthquake disaster in Henan Province and understand the deep seismogenic environment, we have carried out a systematic study on the deep structural characteristics of these active faults. Firstly, based on the high-precision Bouguer gravity anomaly data of Henan Province and its adjacent areas, we obtained the characteristics of gravity anomaly fields at different spatial scales in the study area by using the multi-scale wavelet analysis method. Then the detailed characteristics of different orders wavelets of Bouguer gravity anomaly field in the study area and its relationship with regional structure were analyzed. We found that within 14km of the crust, the regional tectonic activity has an obvious control effect on the trend of gravity anomaly zone. The trend of gravity anomaly zones is obviously different in different tectonic units in the study area. In the north of Henan, the trend of gravity anomaly zones is NE, which is consistent with the regional tectonic trend. The horizontal density difference is obvious. In the south of North China depression and Qinling-Dabie uplift area, the trend of gravity anomaly zones is NW, NWW and EW. In the differential uplift area of western Henan, the trend of gravity anomaly zones is NE. At the 27km depth of the crust, most gravity anomalies are in a clumpy shape, and the consistency between the trend of the gravity anomaly and the regional structure decreases, indicating the differences in regional tectonic stress effect and formation process at different depths of the crust. For example, under the northward compression from Qinling-Dabie uplift, the crust structure in the south of North China depression is different, and the difference gradually decreases from shallow to deep. At the same time, with the increasing of depth, the boundary between Qinling-Dabie uplift and southern North China depression moves to the Pingdingshan and Luohe. Our results show that the regional deep faults have an obvious control over the distribution of gravity anomalies, and the linear transition zone of gravity anomalies often corresponds to the deep faults. In order to obtain the distribution characteristics of active faults in Henan Province and adjacent areas, we analyzed the wavelet multi-scale decomposition of Bouguer gravity anomaly and identified 38 faults. Based on the seismic and geological results, we interpreted the 38 faults, including10 shallow faults in the upper crust with a depth of less than 8km, 15 faults at the bottom of the upper crust with a depth of 12~14km and 13 faults in the lower crust with a depth of 27km. In the study area, the deep faults control the boundary of the first-order tectonic units, such as Liaocheng-Lankao Fault, Tangxi Fault, Xinxiang-Shangqiu Fault, etc., and many moderately strong earthquakes occurred in these faults in history. At last, we analyzed the deep tectonic environment of historical earthquakes with magnitude 6 and above in Henan Province. The results show that the historical earthquakes with magnitude 6 in Xuchang locate near the boundary zone of second-order tectonic units. Other historical earthquakes with M6.0 locate below the secondary uplift or depression controlled by deep and large faults in the crust, such as Puyang earthquake which locates in the Dongpu depression. It can be concluded that the intersections of gravity anomalies zones with different trends, the deep seated fault-controlled intra-crust low gravity anomaly areas, and the intersections of deep seated fault with different strikes are the deep tectonic background and favorable locations for generating earthquakes with magnitude 6 and above in Henan Province. The results of analysis of the characteristics of major deep active faults in Henan Province expanded our understanding of the tectonic environment of the study area and provided a geophysical basis for earthquake prevention and disaster reduction in Henan Province in the future. Table and Figures | Reference | Related Articles | Metrics

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RESEARCH ON COMPREHENSIVE STANDARDIZATION FOR SURVEYING AND PROSPECTING OF ACTIVE FAULT LI Yi-shi SEISMOLOGY AND GEOLOGY    2023, 45 (2): 455-463.   DOI: 10.3969/j.issn.0253-4967.2023.02.009 Abstract （215）   HTML （14）    PDF（pc） （926KB）（190）       Knowledge map    Save Active fault surveying and prospecting is the fundamental work for earthquake prevention and disaster reduction. China began to conduct quantitative research on active faults in the 1980s, and then carried out surveying and prospecting of active faults and seismic hazards assessment in several cities. The results provide a scientific basis for urban land planning, urban disaster prevention planning, construction project site selection and fault setbacks, potential seismic hazards investigation, earthquake emergency preparedness, etc. Standards research in surveying and prospecting of active faults began at the beginning of this century in pace with the development of professional work. Since 2013, the research on the technical system and standards system about surveying and prospecting of active faults was carried out, and a series of standards for technical methods and outcomes were compiled successively. Currently, 1 national standard and 9 sectors standards have been released, and 11 standards are in processing. The national standard GB/T 36072 “Surveying and Prospecting of Active Fault” stipulates the process, content, outcomes, and main technical methods. The 9 sectors standards cover techniques and methods consisting of remote sensing survey, fault geomorphological survey, paleo-seismic trenching, drilling, and fault strip mapping, and stipulate the requirements for the steps, technical indicators, and outcomes of the corresponding technical methods. These standards have become important technical support for active fault survey and prospecting and the main basis for operational supervision. However, there are still many gaps in the standards, and there are obvious contradictions between the supply and demand of the standards. At the same time, the compiling of standards for surveying and prospecting of active faults scattered in different periods and institutions, leading to the problems of function matching and technical indicators coordination among standards. This paper applies comprehensive standardization to surveying and prospecting of active faults, with the objectives to improve the work quality and the application benefit, by regarding the standardization object as a complete system, decomposing comprehensively the relevant elements in three aspects: business process, outcomes and application, and constructing the standard-complex of surveying and prospecting active faults. This is the first attempt to apply comprehensive standardization to the earthquake industry. The working process of surveying and prospecting of active faults can be decomposed into six steps: preparation and revision of implementation plan, determination of fault spatial distribution and parameters, identification of fault activity, analysis of the deep seismic-tectonic environment, assessment of seismic hazards of active faults, and determination of fault deformation zone width. The preparation and revision of the implementation plan comprise data collection, controlled detection, preliminary identification of fault activity, and revision of the implementation plan; the determination of fault spatial distribution and parameters include the implementation and on-site investigation of technical methods such as high-resolution remote sensing interpretation, geological and geomorphic investigation, fault geomorphological survey, geophysical exploration, drilling, paleo-seismic trenching, and dating. The relevant elements of the business process mainly include the work content, technical methods, and technical requirements for project implementation of these links, as well as the technical requirements for project implementation plan preparation and outcomes check and acceptance. The outcomes of surveying and prospecting active faults are divided into survey data, professional outcomes maps, reports, databases, etc. The relevant elements of the outcomes mainly include the technical requirements of the original data and the phased outcomes obtained from the analysis, professional outcomes maps, reports, and databases. The application of surveying and prospecting of active faults is oriented to meet the needs of disaster reduction, and its outcomes are applied to the practice of earthquake prevention and disaster reduction. Relevant elements of application mainly include technical requirements for fault classification and fault cataloging, three-dimensional modeling, hazard assessment, fault avoidance, data management, and information service system construction. Based on the analysis of relevant elements of business process, outcomes, and application, combined with the current status of existing standards, the framework structure of five sequences on surveying and prospecting of active faults standard-complex is put forward, namely, business foundation, project implementation, technical method, outcomes, and application, together with a detailed list of 41 standards. Among them there are 8 items of business foundation, 3 items of project implementation, 15 items of technology and methods, 10 items of outcomes, and 5 items of application. The standard-complex of surveying and prospecting of active faults covers the standards required by the entire business chain, and the standards are interconnected and coordinated. Taking the advantage of the complete set of standards will lay a good foundation for further improving the standardization level of surveying and prospecting of active faults and accelerating the progress of developing standards, and also provide a beneficial demonstration for the high-quality innovative and standardization development of other business areas of earthquake prevention and disaster reduction. Table and Figures | Reference | Related Articles | Metrics

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GEOMETRIC STRUCTURE CHARACTERISTICS OF XINYI SEGMENT OF ANQIU-JUXIAN FAULT ZHANG Hao, WANG Jin-yan, XU Han-gang, LI Li-mei, JIANG Xin, ZHAO Qi-guang, GU Qin-ping SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1448-1468.   DOI: 10.3969/j.issn.0253-4967.2022.06.006 Abstract （548）   HTML （38）    PDF（pc） （16789KB）（188）       Knowledge map    Save The Tanlu fault zone is the most active fault zone in eastern China. It has been active mainly along the Anqiu-Juxian Fault(AJF)since the Quaternary. Predecessors have done a lot of research on the age, paleoearthquake and geometry structure of the AJF, but most of them focus on the exposed area of the fault, and relatively few studies on the buried section. Using field geological survey, shallow seismic exploration, drilling, and paleoearthquake trench, this paper focuses on the geometry structure of the Xinyi section(the buried section)of the AJF, and analyzes its geometry distribution characteristics in the plane and the structural relationship between the deep and the shallow parts, thus filling the gap of the activity characteristics of the Xinyi section of the AJF. The results show that the Xinyi section of the AJF can be divided into three sections from north to south: the Beimalingshan-Guanzhuang section, the Guanzhuang-Tangdian section and the Tangdian-Xindian section. The Xinyi section of the AJF, mainly manifested as strike-slip and normal faulting, has a right-handed and right-step distribution. The step-over zone with~900m in width and~16km in length is dominated by extension, leaving a length-width ratio of 18:1, much larger than the traditional pull-apart basin ratio of 3:1. According to the shallow seismic profile, the shallow seismic line in the Guanzhuang-Tangdian section revealed the extensional fault depression basin on the north side of the terrace, and the bedrock top of the basin gradually became shallower toward the north. The top of the bedrock in the shallow seismic survey line on the north side of the Nanmalingshan suddenly became deeper, and the NNE-trending compressional near-EW basins of the Nanmalingshan and Tashan developed. The two basins were formed from different origin. With the activity of the Anqiu-Juxian Fault and the erosion and deposition of the Shu River, the two basins gradually developed and merged into a composite basin, and the basin structure was consistent with the Quaternary stratigraphic isopach. The Xinyi section of the Anqiu-Juxian Fault presents the deformation characteristics of the same genesis and coordinated geometric structure in the deep and superficial layers, showing a single branch in the deep, cutting through the Cretaceous strata, extending and rupturing upward along the contact interface between the bedrock mountains and the Quaternary soft soil layer in the superficial layer. The fault is shown as a single branch in the north and south Maling Mountains, and ruptured to the surface in many places. In the pull-apart basin in the middle of the fault, the thickness of the Quaternary system is more than 300m. When the Anqiu-Juxian Fault ruptures to the upper part, it divides into two branches, the east and the west, which are concealed and stand opposite to each other in the shape of “Y”, forming the Anqiu-Juxian Fault. On the east-west boundary of the fault, the latest activity is along the west branch of the fault, which is a Holocene active fault. When it extends to the basement rock mass of the Maling Mountains in the north and south, the depth of the upper fault point gradually becomes shallower until it is exposed. The vertical movement of the Xinyi section of the AJF shows the four quadrants characteristics of uplift and subsidence. The extensional area forms a pull-apart basin, while the compressive area constitutes an uplift. The vertical bedrock offset of the Guanzhuang-Tangdian section, with the maximum vertical offset of~230m, gradually decreases to both sides. It can be concluded that the Xinyi section of the AJF presents a spiral-like pivot movement. Table and Figures | Reference | Related Articles | Metrics

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THE PRESENT CRUSTAL DEFORMATION CHARACTERISTICS OF THE HAIYUAN-LIUPANSHAN FAULT ZONE FROM INSAR AND GPS OBSERVATIONS JIANG Feng-yun, JI Ling-yun, ZHU Liang-yu, LIU Chuan-jin SEISMOLOGY AND GEOLOGY    2023, 45 (2): 377-400.   DOI: 10.3969/j.issn.0253-4967.2023.02.005 Abstract （326）   HTML （21）    PDF（pc） （14678KB）（185）       Knowledge map    Save The Haiyuan-Liupanshan tectonic belt is one of the most significant tectonic deformation areas in the northeastern Qinghai-Tibetan plateau with frequent strong earthquakes. It is an important opportunity to study the northeast extension of the Qinghai-Tibetan plateau and an ideal place to study the earthquake breeding process. The published GPS observations show that the southwest side of the Haiyuan fault may still be undergoing deformation caused by the crustal viscoelastic relaxation effect of the 1920 Haiyuan M8.5 earthquake. And the publicly published leveling data results show local vertical deformation of the crust in the area west of the Liupanshan fault is significant. According to the seismic geological data, there exist historical earthquake rupture gaps in the middle and south sections of the Liupanshan fault and the southeast section of the Xiangshan-Tianjingshan fault in the Haiyuan-Liupanshan structural area, which have the background of strong earthquakes above M7.0. In view of the low spatial resolution of GPS and leveling observations, we need to use high-resolution crustal deformation fields to further study the crustal deformation characteristics of the above regions. Therefore, we further discuss the above issues in combination with InSAR observations. The Sentinel-1A/B SAR data of two orbits covering the Haiyuan-Liupanshan fault from 2014 to 2020 were processed to obtain the current crustal deformation field in the line-of-sight direction. Furthermore, the high-density regional crustal deformation field was obtained by integrating InSAR and published GPS observations of the horizontal crustal movement velocity field on a time scale of 20 years. By comparing the observations of GPS, leveling and InSAR and high-resolution three-dimensional deformation integrated GPS-InSAR field, the characteristics of crustal deformation and strain field in the region are analyzed and discussed. The main conclusions are as follows: (1)GPS and InSAR observations show that the post-seismic viscoelastic relaxation effect of the 1920 Haiyuan M8.5 earthquake may still be pronounced on the south side of the Haiyuan fault, but this conclusion is still speculative and needs to be confirmed by further observations; (2)The high-resolution horizontal deformation field from GPS-InSAR shows that the decrease of the sinistral slip rate of the Haiyuan fault along the fault strike mainly occurs in the Middle East section. In contrast, the decrease of the middle and west sections is not significant, which may be related to the transformation of the left-lateral strike-slip to thrust nappe structure between the Haiyuan fault and the Liupanshan fault. (3)GPS vertical and leveling observations both show that the vertical crustal deformation characteristics in the middle and south sections of the Liupanshan fault are similar to the vertical deformation of the Longmenshan fault before the Wenchuan earthquake. Considering the similar structural characteristics of the Liupanshan fault and the Longmenshan fault, and combining with the seismic and geological data, we believe that the Liupanshan fault may be in the relatively late stage of the earthquake breeding process. It can also be recognized by the high-resolution horizontal deformation and strain field derived from GPS-InSAR data. According to the fault motion parameters obtained in our study and the existing seismic and geological data, it is estimated that the maximum moment magnitude of an earthquake in the middle-south section of Liupanshan Mountain is approximately 7.5. (4)The areas with rapid maximum strain accumulation in the study region are mainly concentrated in the vicinity of the Haiyuan fault and the left lateral shear zone between the Haiyuan fault and the Xiangshan-Tianjingshan fault. The dilatation strain rate west of the Liupanshan fault shows prominent compressive deformation characteristics corresponding to the nappe deformation in the Liupanshan tectonic area. The strain rate field in the southeast section of the Xiangshan-Tianjingshan fault is smaller than that of the surrounding area. There is a strain mismatch phenomenon, which may be related to the preparation for strong earthquakes. From the perspective of rotational deformation, the study area presents multiple deformation units, among which counterclockwise rotation corresponds to left-lateral strike-slip deformation(the left-lateral shear belt from the Haiyuan fault to the Xiangshan-Tianjingshan fault). In contrast, clockwise rotation corresponds to right-lateral strike-slip deformation(the right-lateral shear belt in the western margin of Ordos and Longxi block). Table and Figures | Reference | Related Articles | Metrics

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QUANTITATIVE ANALYSES OF GEOMORPHOLOGIC FEATURES IN RESPONSE TO LATE QUATERNARY TECTONIC ACTI-VITIES ALONG THE MAQIN-MAQU SEGMENT, EAST KUNLUN FAULT ZONE LI Zhao, FU Bi-hong SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1421-1447.   DOI: 10.3969/j.issn.0253-4967.2022.06.005 Abstract （388）   HTML （23）    PDF（pc） （28982KB）（183）       Knowledge map    Save The Maqin-Maqu segment(MMS)of the East Kunlun fault zone(EKLF)is located in the seismic gap with a high seismic risk. Study on the geometric characteristics and late Quaternary differential tectonic activity of MMS is critical for carrying out the seismic risk assessment of the cities and towns with relatively high population like the Maqin and Maqu County in the eastern part of EKLF. Previous studies indicated that the late Quaternary left-lateral slip rate along MMS shows an eastward gradient decreasing. However, the geodynamic mechanism to explain this gradient decreasing of slip rate remains controversial. Therefore, accurately identifying the geometric and kinematic characteristics of the major fault zone of MMS and its branch faults can provide important clues for understanding the tectonic transformation mechanism and its seismic risk assessment along the eastern part of EKLF. The geomorphic index can quantitatively describe the geomorphologic characteristics, and effectively extract the active tectonic deformation from surface landscapes. The hypsometric integral index(HI)can well reveal the spatial distribution of the regional tectonic activity intensity by calculating the current three-dimensional volume residual rate of drainage basins. The stream-length gradient index(SL)can effectively reflect the regional tectonic deformation by identifying the geomorphic anomalies of river longitudinal profiles. And the topographic relief(TR)can directly evaluate the geomorphologic erosion in response to the regional tectonic activity. These geomorphic indices have been widely used to differentiate active tectonic deformation regionally. In this study, the geological and geomorphic interpretation of high-resolution remote sensing images are employed to determine the spatial distribution and geometrical features of the major fault zone and branch faults of MMS. The 30m AW3D30 data is used to extract systematically 69 drainage basins along the MMS and adjacent area by GIS spatial analysis technology. Our results indicate that the HI indices along the major fault zone of MMS are much higher in the western segment(0.77~0.89)than in the eastern one(0.15~0.36), and its branch faults like the Awancang Fault(AWCF)and Gahai Fault(GHF)have similar variations. Along the major fault zone of MMS, the TR indices of the Maqin-Oulasuma fault intersection area reach about 400m, and the erosion amounts decrease eastward gradually(middle: 150~180m, east: 50~72m). The TR indices along AWCF also show a trend of decreasing from west(280~350m)to east(18~65m), and the eastern segment(25~100m)of GHF account for~10%~40% of the middle part(~250m). In addition, the distributions of the Hack profile and SLK index vary spatially. In the western segments, rivers with up-convex Hack profiles and higher SLK abnormal values suggest that they are strongly affected by tectonic activity. Thus, the above-mentioned variations of geomorphic index values along MMS show a continuous eastward decreasing, which is displaying a similar trend as the late Quaternary long-term slip rate gradients along MMS. It demonstrates that quantitative geomorphologic analysis is of great indicative function on decoding geomorphologic responses to active deformation processes. Meanwhile, the spatial distribution of geomorphic index values and field geomorphologic investigations reveal that the major fault zone of MMS and its branch faults can be divided into 3 segments, and their activities also show an eastward decreasing. The HI and TR indicate that the turning point of tectonic activity intensity of MMS is near the township of Oulasuma. Therefore, we infer that the slip rate gradient decreasing along MMS might be caused by tectonic transformation and strain distribution of the major fault of MMS together with AWCF and GHF, which are composing a typical horsetail-shaped fault system and play a key role on tectono-geomorphic growth in the eastern part of EKLF. Table and Figures | Reference | Related Articles | Metrics

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NEW PROGRESS IN PALEOEARTHQUAKE STUDIES OF THE JIANGSU SEGMENT OF THE ANQIU-JUXIAN FAULT IN THE TANLU FAULT ZONE ZHANG Hao, LI Li-mei, JIANG Xin, ZHANG Dong, XU Han-gang SEISMOLOGY AND GEOLOGY    2023, 45 (4): 880-895.   DOI: 10.3969/j.issn.0253-4967.2023.04.005 Abstract （1065）   HTML （23）    PDF（pc） （17177KB）（181）       Knowledge map    Save Paleoseismology is a discipline that studies prehistoric earthquakes or earthquakes that occurred before instrumental records using geological and geomorphological methods, mainly by trench excavation and Quaternary chronology. It focuses on the time and intensity distribution of large earthquakes, to reveal the recurrence characteristics of large earthquakes and provide basic data for evaluating the probability of future earthquakes. The Tanlu fault zone is the most active fault zone in eastern China. The Jiangsu section of the Tanlu fault zone is mainly composed of five branch faults, which are strongly active in the Pleistocene. Among them, the Anqiu-Juxian Fault continued to be active until the Holocene, which is the seismogenic fault of the Tancheng 8½ earthquake in 1668. The Xinyi-Sihong section is likely to generate strong earthquakes in the future in the south-central section of the Tanlu fault zone. The total length of the Jiangsu section of the Anqiu-Juxian Fault is about 170km, with an overall strike of 5°~15°, extending southwards from the north Maling Mountain to the Chonggang Mountain. The geomorphic features are distributed from north to south by the alternation of the bedrock mountain and the sedimentary basin. The Anqiu-Juxian Fault shows a single exposed fault on one side of the bedrock mountain, extending to the basin into two branches in the east and west, of which the east branch is the active late Pleistocene Fault and the west branch is the Holocene active fault. The Jiangsu section of the Anqiu-Juxian Fault is dominated by dextral strike-slip and has both dip and thrust components. Lots of research have been done on the ancient earthquakes of the Anqiu-Juxian Fault. The trenches are mostly located in Maling Mountain, Zhangshan Mountain and Chonggang Mountain, which are in the state of uplift and denudation. The Holocene is very thin, and the dating method is mostly optical luminescence. The identification of ancient earthquake events is less since the Holocene, with the accuracy of ancient earthquake time not high and the ancient earthquake sequence not complete. According to the topographic and geomorphological characteristics of the Jiangsu section of the Anqiu-Juxian Fault, three trenches were excavated along the Anqiu-Juxian Fault, of which two were in exposed areas and one in a buried area. Three trenches completely revealed the Holocene sedimentary strata in the Jiangsu section of the Anqiu-Juxian Fault, in which MLTC2 revealed the early Holocene strata, MLTC1 revealed the middle Holocene strata, and HSTC revealed the late Holocene strata. The determination of the age of earthquake events is one of the most uncertain factors in the study of paleoearthquakes and is the main indicator of the recurrence period of paleoearthquakes. At present, most of the paleoearthquake events studied have occurred since the late Pleistocene, and the accuracy of 14C dating is the highest. A total of 13 14C samples were collected from the trenches. Combined with the paleoearthquake events and time revealed by previous trenches, it is concluded that there have been three paleoearthquake events in the Jiangsu section of the Anqiu-Juxian Fault since the Holocene, with theelapsed time of ~3000aBP, ~6000aBP and ~11000aBP, and the coseismic vertical offset are all nearly 1m. The 1668 Tancheng M8½ earthquake showed signs of surface ruptures in the exposed area of the Xinyi section of the Anqiu-Juxian Fault, accompanied by a large amount of sandblasting and water gushing in the buried area. Dense fissures and sand veins are observed in the late Holocene strata overlying the fault, indicating the impact of the 1668 Tancheng earthquake. More representative chronological data are needed as to whether the 1668 Tancheng earthquake ruptured Suqian City. Table and Figures | Reference | Related Articles | Metrics

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GRAIN SIZE AND MICROSTRUCTURE CHARACTERISTICS OF HOLOCENE MEGAFLOOD SLACK WATER DEPOSITS IN THE MIDDLE REACHES OF THE YARLUNG TSANGPO RIVER XU Bo, WANG Ping, WANG Hui-ying, GUO Qiao-qiao, SHI Ling-fan, SHI Yu-xiang SEISMOLOGY AND GEOLOGY    2023, 45 (2): 305-320.   DOI: 10.3969/j.issn.0253-4967.2023.02.001 Abstract （235）   HTML （19）    PDF（pc） （6489KB）（180）       Knowledge map    Save The terrain in southeastern Tibet is steep and the valleys are crisscrossed. Since the Quaternary, glacial ice and debris have blocked the course of the Yarlung Tsangpo River and its tributary river valleys to form giant dammed lakes, and the huge flood deposits formed by the dammed lake outburst floods are often associated with moraines, ice water deposits, lacustrine deposits, aeolian sand or other running water sediments to form complex river valley accumulation landforms. Different types of sediments in alpine and canyon areas are similar in morphology, structure and fabric, and are difficult to distinguish. Grain size and morphological characteristics are the most important structural characteristics of sediment, and the distribution rules are controlled by many factors such as sedimentary environment, physical properties of detrital material, transporting medium and transporting mode, etc., which is an important proxy index for restoring paleoclimate and inverting paleoenvironment. However, the relevant research on identifying sediment types in alpine valley area of southeast Tibet by grain size and morphology index is still in the exploratory stage. In order to understand the particle size characteristics and spatial differentiation laws of outburst flood sediments and the micromorphological characteristics of particle surfaces, we collected 33 samples of Holocene flood retention sediments preserved along the river within about 350km from the outlet of the Jiacha Gorge in the middle reaches of the Yarlung Tsangpo River to Pai Town, and measured them with Malvern 3000 laser diffraction particle size meter and Zeiss Signma scanning electron microscope, combined with digital geomorphology(DEM)data extracted river channel width and steepness coefficient. The features of spatial distribution law of particle size are analyzed, and the following understanding is obtained. The particle size of outburst flood retention deposits is characterized on the whole by fine-silty sand(2.57~5.18Φ)with poor sorting, positive skew and narrow peak state. Two end element models are obtained: The main peak of EM1 terminal element is 3.16Φ, with an average percentage content of 42.7%, which may represent the alluvial characteristics of higher energy of outburst floods in alpine valley areas, and the main peak of EM2 terminal elements is 2.06Φ with an average percentage content of 55.6%, which can be used to indicate the accumulation process of the outburst flood lag deposits. Affected by the width of the river, the EM1 content has a tendency to increase downstream, while EM2 has the opposite trend. The surface microstructure of quartz particles in the outburst flood lag deposits is mainly characterized by mechanical scratches, shell-like fractures, upturn cleavage and cleavage steps, with low structural maturity, mostly angular shape, and rare denudation pores of chemical origin. As a typical representative of climbing sand dunes in the valley area of the semi-humid monsoon area, the genesis of the dunes is of great guiding significance for revealing the source of sand dunes in the valley area of the alpine valley area, identifying paleoflood deposit and aeolian deposit, distinguishing aeolian deposit and paleoflood slackwater deposits on both sides of the riverbank, and windbreak and sand fixation engineering in the Yarlung Tsangpo River. By comparing the particle size and surface micromorphology characteristics of the known outburst flood deposits of the Yarlung Tsangpo River, we believe that the sand source of the Fozhang dunes is mainly from the outburst flood deposits and was transformed later by wind forces. Table and Figures | Reference | Related Articles | Metrics

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EVIDENCE OF LATE QUATERNARY TECTONIC ACTIVITY OF THE BEIDA SHAN FAULT, SOUTHERN MARGIN OF THE ALASHAN BLOCK ZUO Yu-qi, YANG Hai-bo, YANG Xiao-ping, ZHAN Yan, LI An, SUN Xiang-yu, HU Zong-kai SEISMOLOGY AND GEOLOGY    2023, 45 (2): 355-376.   DOI: 10.3969/j.issn.0253-4967.2023.02.004 Abstract （196）   HTML （36）    PDF（pc） （27392KB）（180）       Knowledge map    Save The southern Alashan block is located at the crustal front of the northern Tibetan plateau. It was initially considered as a relatively stable area with weak tectonic activity. In recent years, an increasing number of studies have shown that the Alashan block has undergone significant tectonic deformation since the Cenozoic. Multiple active faults with a horse-tail distribution are developed in the southern margin of the Alashan block. However, there is still controversy over the tectonic deformation patterns of these active faults. One view is that the fault system in the southern margin of Alashan is the result of the eastward extension of the Altyn Tagh Fault and belongs to the tail structure of the strike-slip fault. Another view is that the fault system in the southern Alashan block is the result of the revival of the pre-existing fault caused by the northward compression and thrust of the Tibetan plateau. Therefore, deciphering fault’s kinematics and slip rates since the late Quaternary in the southern Alashan block is crucial to understand the tectonic deformation pattern of the block and its response to Tibet’s northward growth. In this paper, combined with interpretations of remote sensing images and field investigations, we documented the Quaternary activity of the Beida Shan Fault, one of the major faults in the southern Alashan block, along the segment developed in Quaternary alluvium. The Beida Shan Fault is a sinistral strike-slip fault with paralleled north and south branches that displaced the late Quaternary alluvial fans and terraces, forming offset gullies and fault scarps. According to the geometric distribution characteristics, activity and the landforms along the fault, we divided the fault into three segments: the Langwa Shan segment, the northern branch of the Jiapiquan Shan segment, and the southern branch of the Jiapiquan Shan segment. The fault is east-west trending, and the offset geomorphic features along the fault reveal that there are differences in the activity of different segments. The Langwa Shan segment is 10km long and developed at the junction of bedrock and alluvial fan. The fault trace is straight, and a series of gullies and ridges offset by the fault indicate that it is a sinistral strike-slip fault. The Jiapiquan Shan segment is 35km long and divided into two parallel north and south branches with a spacing of about 1.5km. The north branch fault strikes NE on the east side of Langwa Shan and has an angle of about 30° with the south branch fault. After extending about 2km to the northeast direction and entering the north side of Dahong Shan, the fault turns to the EW direction and is parallel to the south branch fault. It is distributed along the boundary between the bedrock and the alluvial fan with the south or north fault scarps and the secondary branch faults. To the east, the north branch fault is developed in bedrock, which is mainly characterized by offset gullies and ridges. The southern branch fault offset multi-stage alluvial fan, forming fault scarps of different heights and left-lateral offset gullies of different scales, and the exposed fault profiles show high angle reverse faults, which dip south or north, indicating that this segment is sinistral strike-slip. Based on the 1.5m resolution DEM data obtained from UAV-SfM, we measured the horizontal displacement of fault landforms using the LaDiCaoZ software developed by Zielke et al.(2012) on the MATLAB platform. Combined with field survey data, we obtained the left-lateral horizontal displacements of 70 sites along the Beida Shan Fault. The sinistral offset of~1m is not included in slip distribution statistics due to limitations of the quantity and data accuracy. Statistical analysis of the displacements reveals that the left-lateral displacements along the fault are concentrated between 3m to 20m, with the majority in two pronounced peaks at 5.3m and 10.1m. The 5.3m peak contains the most data points, with 17 displacements data, accounting for 24% of the total, while the 10.1m peak contains 6 data points, accounting for 9% of the total. This indicates that the Beida Shan Fault has experienced multiple seismic events involving the displacement and rupture of stratigraphic layers on the surface. An~8km-long surface rupture is discovered on the south fault branch, and it is represented by of fault scarps and of tens of centimeters 1~2m left-lateral displacement of small gullies. Fresh surface rupture and left-lateral offset gullies indicate the latest fault activity. Using the previously dated alluvial fan ages in Taohuala Shan, ~30km south of the Beida Shan, we calculated the late Pleistocene sinistral slip rate of 0.3~0.6mm/a along the Beida Shan Fault, which is consistent with the slip rate of the Taohuala Shan Fault estimated by Yu et al.(2017). Compared with the fault slip rate accommodated in the Hexi Corridor area and regional GPS rates, the southern Alashan block plays a significant role in absorbing deformation in response to the northern Tibetan growth. 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GEOLOGICAL DEFORMATION OF THE TUOLI FAULT IN THE WEST JUNGGAR SINCE THE LATE QUATERNARY YUAN Hao-dong, LI An, HUANG Wei-liang, HU Zong-kai, ZUO Yu-qi, YANG Xiao-ping SEISMOLOGY AND GEOLOGY    2023, 45 (1): 49-66.   DOI: 10.3969/j.issn.0253-4967.2023.01.003 Abstract （229）   HTML （47）    PDF（pc） （11448KB）（178）       Knowledge map    Save In the Cenozoic, under the influence of the collision of the India-Eurasia plate and the northward pushing after that, deformation occurred in the interior of the continent, and the crustal deformation is mainly absorbed by the thickening of the crust and the strike-slip movement of the fault. The GPS velocity field shows that the area north of Tianshan absorbs the shortening with a rate of~2mm/a. How the shortening with these rates is absorbed is a topic worthy of study. The West Junggar, located to the north of the Tianshan Mountains and developed with the inclined parallel strike-slip fault system is an important area of crustal shortening. The inclined parallel strike-slip fault system includes the east Tacheng Fault, Tuoli Fault and Daerbute Fault. Hence, the structural deformation of the Tuoli Fault in the late Quaternary is significant for understanding the structural deformation and crustal shortening absorption mode in the north of Tianshan Mountains. In this study, two branches were found extending along the Tuoli Fault in the direction of NE based on remote sensing image interpretation. Field investigation to the two branch faults shows that many marker landforms were dislocated in the study area, including gullies and terrace riser. The two faults cross through the terraces developed in the Kapusheke River and the Tiesibahan River in this area, forming offset terrace riser. Because the terrace riser is in the retained bank of the river, the upper-layer terrace model is used to calculate the fault’s slip rate. The gullies are mainly distributed on the T3 terrace of the Kapushek River on the west branch fault. The horizontal dislocation of these gullies ranges from 10m to 37.5m, and the largest horizontal dislocation is located in the No. 8 gully, which is (37.5-4.1/+2.7)m. Since the actual value of the fault movement rate must be greater than the rate obtained by the sub-gully offset, we choose the maximum offset of the gully on the landform surface in calculating the slip rate. We used OSL(Optical Stimulated Luminescence)to date the age of the landform and used UAV(Unmanned Aerial Vehicle)photogrammetry technology to extract high-precision DEM of the study area. Then, we calculate the movement rate of the Tuoli Fault since the late Quaternary from the dislocations and the age of landmark landforms such as gullies and terraces. The results show that the Tuoli Fault comprises two branch faults in the east and the west, both of which are left-lateral horizontal strike-slip. The east branch fault produced a (89±31)m and (39±13)m horizontal dislocation on the T3 and T2 terrace of the Kapusheke River, respectively. Combined with the (52.9±5.1)ka of the T3 terrace age and (23.4±1.5)ka of the T2 terrace age, the horizontal slip-rate of (1.7±0.8)mm/a is calculated for the eastern branch fault. The western branch fault produced a horizontal dislocation of (34.0±6.8)m on the T2 terrace of the Tiesibahan River and 37.5(-4.1/+4.1)m of the gully on the T3 terrace of the Kapusheke River. Combined with (18.8±1.3)ka of the T2 terrace age, we obtained a sinistral slip rate of 1.8(+0.5/-1.3)mm/a for the western branch fault. The sinistral slip rate of two branch faults of the Tuoli Fault is similar to the sinistral slip rate of the east Tacheng Fault in the previous research results. This study result indicates that these parallel left-lateral strike-slip faults in the West Junggar area conform to the characteristics of the bookshelf faults structural model, and most of the compression shortening in the West Junggar area is absorbed by the parallel strike-slip movement of the fault system. So this fault system has played an important role in controlling the NS shortening of the crust in this region. Table and Figures | Reference | Related Articles | Metrics

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LATE QUATERNARY SHORTENING RATE OF THE SANSUCHANG ANTICLINE, SOUTHERN LONGMEN SHAN FORELAND THRUST BELT ZHANG Wei-heng, CHEN Jie, LI Tao, DI Ning, YAO Yuan SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1351-1364.   DOI: 10.3969/j.issn.0253-4967.2022.06.001 Abstract （386）   HTML （96）    PDF（pc） （7558KB）（178）       Knowledge map    Save Fold scarps, a type of geomorphic scarp developed near the active hinge of active folds due to the local compressive stress, are formed by folding mechanisms of hinge migration or limb rotation. At present, there are several proven methods, which are only based on the fold scarp geometry combined with the occurrences of underlying beds and do not use the subsurface geometry of thrust fault and fold to obtain the folding history. The use of these methods is of great significance to illuminate the seismic hazards and tectonic processes associated with blind thrust systems. The Sansuchang fold-thrust belt is a fault-propagation anticline controlled by the Sansuchang blind thrust fault located in the southern Longmen Shan foreland area. Previous study used the area-depth method to calculate the shortening history of the Sansuchang anticline since the late Pleistocene(73~93ka)based on the terrace deformation of Qingyijiang River. However, due to the serious erosion damage to the terrace after its formation, the shortening history obtained by incomplete terrace deformation needs to be further verified. A~9km long scarp was found on the Dansi paleo-alluvial fan on the eastern limb of the Sansuchang fold-thrust belt. According to the detailed field investigation and the fold geometry built by the seismic profile, we found the scarp is near the synclinal hinge, which separates beds dipping 10°~17° and 43°~57° east and parallels with the Sansuchang fold hinge. Therefore, we determined the scarp is a fold scarp formed by the forelimb hinge migration of the fault-propagation fold. The maximum height of the scarp, extracted by the swath topographic profile across the scarp, is about 28~35m. According to the parameters of the fold scarp height, the underlying beds dip angle near the fold scarp, and the quantitative geometric relationship between shortening and the blind Sansuchang thrust fault, it can be estimated that, after the deposition of the Dansi paleo-pluvial fan((185±19)ka), the anticline forelimb horizontal shortening rate is~0.1mm/a, the fault tip propagation rate of the Sansuchang blind fault is(0.5+0.3/-0.1)mm/a, and the total shortening rate of the Sansuchang anticline is(0.3+0.2/-0.1)mm/a. The folding rates of the Sansuchang fold-thrust belt since the late middle Pleistocene has been obtained by the local deformation characteristics of the fold scarp in this study. The result is basically consistent with the shortening rate since late Pleistocene obtained by complete terrace deformation across the anticline, which proves that the shortening rate of the Sansuchang anticline is relatively stable at~0.3mm/a. It provides a new idea for studying the activity characteristics of fold-thrust belts in the southern Longmen Shan foreland thrust belt area with a fast denudation rate and discontinuous geomorphic surface. Table and Figures | Reference | Related Articles | Metrics

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PALEOEARTHQUAKES AND VERTICAL SLIP RATES ON THE HUAI RIVER-NÜSHAN LAKE SEGMENT OF FAULT F5 IN THE MIDDLE SECTION OF THE TANLU FAULT ZONE YANG Yuan-yuan, LI Peng-fei, LU Shuo, SHU Peng, PAN Hao-bo, FANG Liang-hao, ZHENG Hai-gang, ZHAO Peng, ZHENG Ying-ping, YAO Da-quan SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1365-1383.   DOI: 10.3969/j.issn.0253-4967.2022.06.002 Abstract （498）   HTML （50）    PDF（pc） （11724KB）（176）       Knowledge map    Save The Anqiu-Juxian Fault(F5)in the middle part of Tanlu fault zone is the most important seismically active fault in eastern China. The Fault F5 is divided into the Anqiu-Juxian section, the Juxian-Tancheng section and the Xinyi-Sihong section, each of which is an independent rupture unit. There are no historical records about earthquakes with magnitude above 5 in the Xinyi-Sihong section, but it is revealed that there are Holocene paleoseismic events, so this section is a significant gap segment of surface rupture of historical earthquakes. In recent years, an important progress in the study of neotectonic activity of Xinyi-Sihong section of F5 is to find that it extends southward to the region between Huai River and Nüshan Lake in Anhui Province, with a length of about 20km. The fault spreads on the gentle slope on the edge of Cretaceous red sandstone uplift(hillock)along the line from Fushan to Ziyangshan, and the latest activity can date back to the early Holocene. At present, there is a clear understanding of the geometric distribution, structural characteristics and activity nature of the Huai River-Nüshan Lake section of F5(F5-HRNL), but the paleoseismic research is relatively weak, the revealed paleoseismic events are relatively sporadic, and the research results are from single trench, so there is a lack of comprehensive and comparative analysis from multiple trenches. In addition, the study on slip rate has not been carried out in this section, which affects the understanding of the overall activity level of the fault. Therefore, based on the previous work, paleoseismic research is carried out by excavating trenches in key locations, and more reliable paleoseismic events are determined through comprehensive comparative analysis of multiple trenches. The vertical slip rate of the fault is calculated by measuring the height of the fault scarp near the trench and combining with the dating data of relevant strata. Based on the paleoseismic research results of the F5-HRNL and combined with the data of other disciplines, the seismic risk of this fault section is analyzed. The results of this study enrich the understanding of the overall activity characteristics of F5 in the Tanlu fault zone in the Late Quaternary, and provide new data for medium- and long-term earthquake prediction in the border area of Jiangsu and Anhui Provinces. In this study, a new trench was excavated at the foot of Fushan Mountain on the south bank of the Huai River, named Santangnan trench, for the special research on ancient earthquake events. The trench reveals that four paleoseismic events have occurred on F5, and the latest event occurred since the late Late Pleistocene, that is, since(15.7±2.0)ka BP, but the trench failed to constrain the age of each event. Based on the trenching work and combined with the previously published trench research data, the paleoseismic events in the F5-HRNL are further constrained by using the progressive constraining method. The results show that at least five paleoseismic events have occurred in the F5-HRNL since the late Middle Pleistocene. The first three events occurred in the late Middle Pleistocene to the late Late Pleistocene, all of which were thrust in nature and manifested as gently dipping thrust faults, reverse faulting colluvial wedges and structural wedges in the trench; the latest two events occurred since the late Late Pleistocene, both of which were extensional in nature and manifested as splitting wedges in the trench; the age of the latest two events are constrained at 20.36~(18.7±0.3)ka BP and 10.92~7.83ka BP respectively. At present, the research on the slip rate of F5 mainly focuses on the horizontal slip rate on the Shandong Province section, where the water systems are relatively developed and the deformation is obvious. The vertical slip rate of the fault is rarely reported. Stable and continuous fault scarps are developed in local segments of the F5-HRNL, and trenches are excavated across the scarps, which provides support for the calculation of vertical slip rate of this section. Through UAV topographic mapping, a high-precision digital elevation model near the scarp is constructed, the topographic profile across the scarp is extracted, and the vertical displacement of the fault is discussed. Based on the results of Quaternary stratum dating and paleoseismic event analysis in the trench near the scarp, the starting time of vertical displacement of the scarp is determined. The calculation shows that the vertical slip rate of the F5-HRNL is about 0.05mm/a in the Ziyangshan area and about 0.07mm/a in the Doushan area, indicating that this fault section is weakly active as a whole. The Sihong-Mingguang section of F5 is from the south of Chonggang Mountain in Sihong County, Jiangsu Province to the north of Nüshan Lake in Mingguang City, Anhui Province, with a total length of about 65km. The latest paleoseismic event revealed in this section is about 8 000 years ago. Based on the research results of paleoearthquakes and combined with the research data of other disciplines, it is considered that the F5 Sihong-Mingguang section is the surface rupture gap section of historical earthquakes, a long time has elapsed since the latest ancient earthquake, and the current small earthquakes are not active, the locking degree is high, and it is likely to accumulate stress, and there is a risk of strong earthquakes of magnitude 7 or above. Table and Figures | Reference | Related Articles | Metrics

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EMPIRICAL QUANTITATIVE ANALYSIS OF STRENGTH AND SEISMOGENIC DEPTHS FOR THE BRITTLE-DUCTILE TRANSITION OF CONTINENTAL FAULT ZONE LEI Hui-ru, ZHOU Yong-sheng SEISMOLOGY AND GEOLOGY    2023, 45 (1): 29-48.   DOI: 10.3969/j.issn.0253-4967.2023.01.002 Abstract （279）   HTML （38）    PDF（pc） （5275KB）（176）       Knowledge map    Save The strength properties of fault rocks at shearing rates spanning the transition from crystal-plastic flow to frictional slip play a central role in determining the distribution of crustal stress, strain, and seismicity in a tectonically active region. Since the end of the 20th century, many experimental and modelling works have been conducted to elucidate the variation of the strength profile and mechanism of brittle-ductile transition(BDT)with temperature, pressure, and sliding rate. We review the substantial progress made in understanding the physical mechanisms involved in lithospheric deformation and refining constitutive equations that describe these processes. The main conclusions obtained from this study are as follows: (1)The mechanical data and microstructure of friction and creep experiments indicated the transition from brittle to plastic deformation with the increasing crust depth, which not only controls the ultimate strength of the crustal profile but also limits the lower limit of the seismogenic zone. Moreover, based on the variation of rock characteristics, temperature, normal stress and sliding rate, the brittle-ductile transition zone distributes at different depths in the crust. The strength profile consisting of friction law and flow law is widely used to describe the strength and seismicity of the continental crust. However, this profile model is oversimplified in the BDT zone because this area involves a broad region of semi-brittle behavior in which cataclastic and ductile processes occur. At the same time, the model also lacks characterization of the transient dynamic properties of faults. Rate-and-state friction(RSF)law stipulates that the occurrence of slip instabilities(i.e. earthquake)can be linked with the velocity dependence of friction. Therefore, the RSF equations, when applied to the kilometer-scale of fault zones, models incorporation RSF equations can reproduce several important seismological observations, including earthquake nucleation and rupture, earthquake afterslip, and aftershock duration. However, these key microphysical processes of fault gouge evolution are unknown to this model. (2)During numerical model-fitting experimental observations, the Friction-to-flow constitutive law merges crustal strength profiles of the lithosphere and rate dependency fault models used for earthquake modelling on a unified basis, which is better than controlling the boundary of BDT using the Mohr-Coulomb criterion, Von Mises criterion and Goetze’s criterion. The Friction-to-flow constitutive law can predict the steady-state and transient behavior of the fault, including the response of shear stress, sliding rate, normal stress, and temperature, in addition to simulating the transition of fault sliding stability from velocity-weakening to velocity-strengthening. It also solved seismic cycles of a fault across the lithosphere with the law using a 2-D spectral boundary integral equation method, revealing dynamic rupture extending into the aseismic zone and rich evolution of interseismic creep, including slow slip before earthquakes. However, these constitutive models do not base on microphysical behavior. Furthermore, at low to intermediate temperatures, the ductile rheology of most crystalline materials are different from those at high temperatures. (3)A recent microphysical model, which treats fault rock deformation as controlled by competition between rate-sensitive(diffusional or crystal-plastic)deformation of individual grains and rate-insensitive sliding interactions between grains(granular flow), predicts both transitions well, called the CNS model. Unlike the numerical model, this model quantitatively reproduces a wide range of(transition)frictional behaviors using input parameters with direct physical meaning, which is closer to the natural strength of the fault. This mechanism-based model can reproduce RSF-like behavior in microstructurally verifiable processes and state variables. However, the major challenge in the CNS model lies in capturing the dynamics of micro- and nanostructure formation in sheared fault rock and considering the different processes of rock deformation mechanisms. Since it is microphysically based, we believe the modelling approach can provide an improved framework for extrapolating friction data to natural conditions. Table and Figures | Reference | Related Articles | Metrics

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RELOCATION OF THE 2022 MS6.0 MAERKANG EARTHQUAKE SWARM IN SICHUAN PROVINCE AND ITS SEISMIC FAULT ANALYSIS XU Ying-cai, GUO Xiang-yun SEISMOLOGY AND GEOLOGY    2023, 45 (4): 1006-1024.   DOI: 10.3969/j.issn.0253-4967.2023.04.012 Abstract （190）   HTML （21）    PDF（pc） （13832KB）（169）       Knowledge map    Save The 2022 MS6.0 Maerkang earthquake swarm in Sichuan Province is the first rare strong swarm activity with high frequency, concentrated spatial and temporal distribution, strong explosive and strong magnitude in Maerkang area in the eastern segment of Bayan Har block in China seismic network records. It is also another significantly strong earthquake event in Bayan Har block after the MS7.4 Maduo earthquake on May 22, 2021. The MS6.0 Maerkang earthquake on June 10, 2022 not only broke the 33-year record without MS≥6.0 earthquakes within 100km of the epicenter, but also broke the historical record without MS≥6.0 earthquakes within 50km of the epicenter. The earthquake swarm is mainly located in the nearly “T” shaped conjugate fault structure area composed of the NW strike Maerkang fault and NE strike Longriba fault in the Bayan Har block. This area is a relatively rare region for moderate and strong earthquakes in the history. Therefore, it is of great significance to analyze and discuss the possible seismogenic faults of the Maerkang strong earthquake sequence for the study of seismogenic structures and the risk of strong earthquakes in the weak seismic region of Bayan Har block. The earthquake swarm was relocated by double-difference method, and focal mechanisms and centriod depths of MS≥3.6 earthquakes were calculated by using gCAP inversion method. Then the relationship between the stress system in the Malkang area and these earthquake focal mechanisms was analyzed, and fault plane was fitted by using relocation results. Maerkang earthquake swarm is mainly distributed along NW direction, and the initial rupture depth is 9.8km on average. Depth profiles show that earthquakes are mainly concentrated at depth between 0km to 15km. The most earthquakes of early-stage occurred in 48 hours. The mid-stage and late-stage earthquakes are located less than 15km in depth and move to the northwest of the epicenters. Initial rupture depth of the largest MS6.0 earthquake is 12.5km, which is almost at the bottom of the dense area. The focal mechanism of MS6.0 earthquake is 150° in strike, 79° in dip, and 7° in rake on nodal plane Ⅰ, and 59° in strike, 83° in dip, and 169° in rake on nodal plane Ⅱ, with the centroid depth of 9km. Other focal mechanisms of MS≥3.6 earthquake are strike-slip types. Dips of nodal plane of focal mechanism range from 71° to 86°, and there exist different dip directions for one strike of every nodal plane. All azimuths of P axis are in NWW direction, and the plunges are nearly horizontal. The focal mechanisms of MS≥3.6 earthquakes show that the tectonic environment is very favorable for NE or NW strike faults to generate the strike-slip movement. Centriod depths range from 5 to 9km, which are lower than the average depth of 9.8km of relocation, indicating that these earthquakes mainly ruptured from deep to shallow. The relative shear stress of the NW nodal plane are significantly greater than that of the NE nodal plane, and the normal stress of the NW nodal plane was smaller than that of the NE nodal plane, indicating more possibility of strike-slip dislocation on the NW nodal plane. The fault plane fitting results reveal that there are obviously two nearly parallel and nearly NW strike earthquake belts in the epicenter area. Fitted fault plane parameters of the belt in the north branch show the strike 333°, the dip 88°, the slide -22°, and the belt in the south branch show the strike 331°, dip 88°, and slide -23°. It is indicated that the fault properties of these two earthquake belts are basically the same, revealing that most of earthquake activities of the swarm may be controlled by at least two parallel structures near the Maerkang fault with the NW strike, dip 88° and left-lateral strike-slip. Combined with the existing regional geological structure, it is inferred that the Maerkang earthquake swarm may be induced by the NW and NE strike conjugate faults, and the NW strike faults control most of the earthquake activities. Table and Figures | Reference | Related Articles | Metrics

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INTERSEISMIC SLIP RATES AND SHALLOW CREEP ALONG THE NORTHWESTERN SEGMENT OF THE XIANSHUIHE FAULT FROM INSAR DATA CHEN Yi, ZHAO Bin, XIONG Wei, WANG Wei, YU Peng-fei, YU Jian-sheng, WANG Dong-zhen, CHEN Wei, QIAO Xue-jun SEISMOLOGY AND GEOLOGY    2023, 45 (5): 1074-1091.   DOI: 10.3969/j.issn.0253-4967.2023.05.003 Abstract （160）   HTML （19）    PDF（pc） （10431KB）（167）       Knowledge map    Save Located in the eastern boundary of the Qinghai-Tibetan plateau, the Xianshuihe fault zone is one of the most active left-lateral strike-slip faults in Chinese mainland. As the southern boundary of the Bayanhar block, the Xianshuihe Fault accommodates the southeastward transport of material toward southeastern Asia. Earthquakes have occurred frequently along this fault, especially in the northwestern segment. More than 20 earthquakes with MW>6.0 have ruptured since 1700. The most recent MW>7 earthquake was the Luhuo earthquake in 1973, and the most recent MW>6 earthquake was the MW6.6 Luding earthquake in 2022. As one of the most active faults in mainland China, the present slip pattern of the Xianshuihe Fault, especially the shallow creep characteristics along its northwestern segment, has attracted much attention. The primary goal of determining slip rates of active faults using geodetic data is to quantify the seismic potential of the faults. Illuminating the long-term slip rate and shallow creep distribution of faults is the basis for calculating the seismic moment rate and evaluating the seismic potential. Due to the backwardness of early measurement methods, the seismic deformation along the Xianshuihe Fault was previously based on geologic, cross-fault short baseline and leveling surveys. With the application of GPS in tectonic geodesy, more and more GPS stations are installed near active faults, which provide accurate constraints on the long-term slip rates of the fault. Subsequently, the appearance of InSAR technology has brought a beneficial supplement to GPS, providing high spatial resolution surface velocity maps, which have been widely used to measure deep and shallow creep along active faults. It is the key to accurately characterize the fault slip behavior and evaluate the seismic potential. In this study, 119 Sentinel-1 satellite descent data from December 2014 to December 2021 were processed to obtain the average line-of-sight(LOS)velocity field of the northwestern segment of the Xianshuihe Fault based on the small baseline InSAR method. Then the elastic screw dislocation model was used to fit the fault normal InSAR LOS velocity profiles to estimate the long-term slip rates and shallow creep rates. Combined with the viscoelastic earthquake cycle model, the effects of the earthquake recurrence period, and rheology of the lower crust and upper mantle on slip rate estimation in Luhuo segment are analyzed. The main results are as follows: (1)The average InSAR LOS velocity field is in the northwestern segment of the Xianshuihe Fault during 2014—2021 has been obtained with a large range and high spatial resolution. The velocity field results show an obvious velocity gradient across the surface trace of the Xianshuihe Fault, which is consistent with the left-lateral strike-slip characteristics of the Xianshuihe Fault. (2)To investigate the slip rate variation along the northwestern segment of the Xianshuihe Fault, we used the two-dimensional elastic screw dislocation model to fit the 14 fault-normal velocity profiles selected along the northwestern segment of the Xianshuihe Fault and estimated the long-term slip rates and shallow creep rates using the Markov Chain Monte Carlo(MCMC)method. The results show that the overall slip rates of the NW segment of the Xianshuihe Fault range from 7.2mm/a to 11.0mm/a, and gradually decrease from west to east. The shallow creep rate ranges from 0.3mm/a to 3.1mm/a. The high creep rate appears mainly at Xialatuo and the segment from Daowu to Songlinkou. The shallow creep rates in other places are close to zero, implying that the fault is completely locked. (3)According to historical earthquake records, the recurrence interval of the Luhuo segment is set to be 150 years, 200 years, and 400 years, and the viscosity of the lower crust and upper mantle is set to be 5.0×1018Pa·s, 1.0×1019Pa·s, and 5.0×1019Pa·s. The slip rate of the Luhuo segment is estimated to be (7.91±0.3)~(9.85±0.4)mm/a using the MCMC method, which is slightly lower than the (10.14±0.5)mm/a obtained by the pure elastic model. In addition, when the earthquake recurrence interval is 150 years and the viscosity of the lower crust and upper mantle is 5.0×1019Pa·s, we simulate the fault-normal velocity at 5 years, 20 years, 75 years, and 125 years after the 1973 Luhuo earthquake, and find that in any period of the seismic cycle, the estimation of fault slip rate will be biased to some extent if the viscoelastic contribution of the lower crust and upper mantle is ignored. Table and Figures | Reference | Related Articles | Metrics

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A PRELIMINARY STUDY OF THE SHALLOW EXPLORATION AND QUATERNARY ACTIVITIES OF THE FENGQIU SEGMENT OF THE XINXIANG-SHANGQIU FAULT TIAN Yi-ming, YANG Zhuo-xin, WANG Zhi-shuo, SHI Jin-hu, ZHANG Yang, TAN Ya-li, ZHANG Jian-zhi, SONG Wei, JI Tong-yu SEISMOLOGY AND GEOLOGY    2023, 45 (1): 139-152.   DOI: 10.3969/j.issn.0253-4967.2023.01.008 Abstract （247）   HTML （22）    PDF（pc） （9154KB）（167）       Knowledge map    Save Xinxiang-Shangqiu Fault starts from Yuhekou in the west and extends eastward into Anhui Province through Xinxiang, Yanjin, Fengqiu, Lankao, Minquan, Shangqiu and Xiayi, with a total length of about 400km and a general strike of NWW. It is a regional concealed fault in Henan Province and a boundary fault between northern North China depression and southern North China depression. This study focuses on the Fengqiu section of Xinxiang-Shangqiu Fault, which is the boundary structure between the Kaifeng sag, Neihuang uplift and Dongpu sag. Controlled by the NE-NEE trending Changyuan Fault and Yellow River Fault at its east and west end, this fault section has a length of about 30km and controls the Mesozoic to early Cenozoic sedimentation in the Kaifeng sag and the south side of Dongpu sag. In this paper, the shallow structural characteristics and Quaternary activities of Fengqiu section of the Xinxiang-Shangqiu Fault are revealed by the combination of reflection seismic exploration and drilling detection. Two shallow seismic exploration profiles and one composite drilling geological section are arranged across the fault. The results of shallow seismic exploration show that the Fengqiu section of Xinxiang-Shangqiu Fault is NWW trending. It is a north-dipping normal fault accompanied by several nearly parallel normal faults, and the fault is still active since the Quaternary. In the composite drilling geological section at Yaowu, the latest faulted stratum is a clay layer between borehole YW5 and YW7, and the buried depth of the upper breakpoint is between 57.00~61.50m. Combined with the dating results of the collected samples, it is comprehensively judged that the latest activity age of Fengqiu section is the middle of late Pleistocene. Since the middle of late Pleistocene, the whole region is in a relatively stable tectonic period. It is verified that the comprehensive detection method of shallow seismic exploration with drilling can effectively find out the accurate location of hidden faults. The zone with strong vertical differential movement is often the zone where earthquakes occur. The vertical differential movement between Kaifeng sag and Neihuang uplift is very strong, and the difference reaches nearly 1^{}000 meters since Neogene. Moreover, the structural pattern of the main strong earthquakes in the North China Plain is characterized by zoning in NE direction and segmentation in NW direction, especially at the intersections of NWW-trending faults and NE-trending faults. The Xinxiang-Shangqiu Fault intersects with a series of NE-NEE trending faults, including Tangdong, Changyuan, Yellow River and Liaolan faults from west to east. The Fengqiu section is at the intersection with the Changyuan Fault and the Yellow River Fault, and is located in the Fengqiu M6.5 potential seismic source area of the North China plain seismic belt. The intersection of two groups of Quaternary active faults is a favorable place for the preparation and generation of moderate and strong earthquakes. Therefore, the research results provide seismological basis for the site selection of major engineering projects, urban planning and construction in this area, and have reference value for discussing the geodynamic issues such as deep and shallow structural relationship and structural evolution of Xinxiang-Shangqiu Fault. Table and Figures | Reference | Related Articles | Metrics

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NEW UNDERSTANDING OF THE MAGMA EVOLUTION OF CHANGBAISHAN-TIANCHI VOLCANO BASED ON MELTS SIMULATION ZHOU Bing-rui, PAN Bo, YUN Sung-hyo, CHANG Cheol-woo, YAN Li-li SEISMOLOGY AND GEOLOGY    2022, 44 (4): 831-844.   DOI: 10.3969/j.issn.0253-4967.2022.04.001 Abstract （635）   HTML （84）    PDF（pc） （6476KB）（166）       Knowledge map    Save Changbaishan-Tianchi volcano(CBS-TC), located in Jilin Province on the border between China and North Korea, is the largest composite volcano around China, which is still active. The eruption stages of this large Quaternary composite volcano can be roughly divided into 2.0~1.48Ma shield forming stage, 1.48~0.05Ma cone forming stage and the explosive eruption stage since 50000 years ago. Its great eruption activities(the Millennium Eruption)from 946AD to 947AD and magmatic disturbances from 2002 to 2005 have attracted great attention of the government and scholars. Predecessors have done a lot of researches on Tianchi volcano, including its eruption periods, distribution of eruptive products, disaster assessment and so on. Geophysical data show that there are anomalies in the lower part, indicating the existence of magma chambers or conduits, but the accurate boundary and depth of magma chambers need to be further explored. The study of petro-geochemistry shows that the products of shield forming stage of Tianchi are mainly potassic trachy-basalts. The MgO# of these basic magma is lower than that of the primary magma in Northeast China, indicating that they are the evolved magma undergoing the process of fractional crystallization. In the past, the cone forming stage was considered to have the characteristic of “bimodal” eruptions, that is, the cone forming eruptions of high SiO2 trachytic/comenditic magma was accompanied by the low SiO2 basaltic magma, which formed small cinder cones on the edifice. In recent years, some drilling data show that there are thick basaltic trachy-andesite and trachy-andesite strata under the cone, indicating that the products of the cone forming stage of Tianchi include early basaltic trachy-andesite, medium trachy-andesite and late trachyte. Their SiO2 and Na2O+K2O contents are increasing with the degree of evolution. Since the late Pleistocene, Tianchi volcano has entered the stage of explosive eruptions with strong caldera forming effect. The eruptive products are mainly comenditic/trachytic airborne pumice, ignimbrite and so on. However, there are still many disputes about the magmatic evolution of CBS-TC, especially the evolution process from basalt to trachy-andesite, trachyte and comendite. In this study, we did abundant field geological investigation and collected rock samples of each eruptive stage of CBS-TC, and carried out whole-rock geochemical analysis. The results show that major elements of these samples have continuous linear trends with increasing of SiO2 content in magma, and the distribution of rare earth elements and trace elements is also consistent, which indicates a continuous evolution process. Meanwhile, compared with intermediate-basic magma, the trachyte and comendite magma in Tianchi has a characteristic of high Th/La and 87Sr/86Sr values, indicating that the magma has also experienced assimilated contamination by crustal materials. In order to verify this fractional crystallization with assimilation(AFC)process of Tianchi magma, the author uses petro-thermodynamic simulation(MELTS model)to calculate the magma evolution. The condition parameters used in the simulation include temperature, pressure, oxygen fugacity, water content, etc. Those parameters are considered as close as possible to the real situation in the magma system. The conditions of pressure and water content are still controversial, which are limited by this simulation. It is found that the evolution of Tianchi magma tends to have occured under the conditions of low pressure(2kbar)and high water content(≥0.5wt%), and about 10% granitic assimilates were mixed in the late stage of evolution, which is consistent with the previous research on the location of magma chambers and melt inclusions. The simulation results are consistent with the trends of tested major elements of Tianchi volcano. To sum up, we found that besides fractional crystallization, assimilation and contamination of shallow crustal granite also play an important role in the evolution of basalt to comendite. In this paper, the magmatic evolution of Tianchi volcano has been studied systematically, during which the method of petro-thermodynamic simulation combined with geochemical analysis is used. A series of new understandings have been obtained, including the eruption sequence, magmatic evolution, and contamination processes of Tianchi volcanic rocks. This analysis procedure provides a certain reference for the future study. The conclusions help to better understand this largest active volcano in China, and provide new ideas for interpretation of volcanic monitoring data, which helps prevent volcanic disasters. The study also provides references for the regional construction planning of the government. Table and Figures | Reference | Related Articles | Metrics

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THE RESPONSE OF FLUVIAL LANDFORM TO THE EVOLU-TION OF FAULT STRUCTURE IN THE NORTHERN ZHONGTIAO MOUNTAINS FAULT LU Ben-tian, LI Zhi-gang, LIANG Hao, YANG Jing-jun, ZHENG Wen-jun SEISMOLOGY AND GEOLOGY    2022, 44 (4): 961-975.   DOI: 10.3969/j.issn.0253-4967.2022.04.009 Abstract （510）   HTML （36）    PDF（pc） （7104KB）（164）       Knowledge map    Save As an important part of the land geomorphic unit, river is one of the main geological forces to shape the surface morphology. The fluvial geomorphic development characteristics are extremely sensitive to tectonic activities and record rich tectonic deformation information in geological history. Therefore, through the information extraction and quantitative analysis of bedrock river, we can reverse the relevant information about the tectonic evolution history. By extracting topographic information, comprehensively analyzing the spatial differences of fluvial geomorphological parameters, sieving the influencing factors such as tectonic, climatic and lithological characteristics, and quantifying the intensity of tectonic activity have become an important research tool for the segmental differences of active faults. The Northern Zhongtiao Mountains Fault is an active fault that controls the uplift of the Zhongtiao Mountains and subsidence of the Yuncheng Basin, and can be divided into the Hanyang, Yongji, Yanhu and Xiaxian sections from south to north. The activity of each section of the fault is closely related to the shaping of the present-day topography of the Zhongtiao Mountains, and it is a typical area for applying quantitative analysis of fluvial landform to the study of the segmentation differences along the fault. So we can effectively study the distribution characteristics of tectonic activity in the fault zone through the river geomorphological features of Zhongtiao Mountains. In this paper, by extracting information on the river topography of the bedrock mountain watershed system on the northern slopes of the Zhongtiao Mountains, parameters such as the normalized steepness index ksn, slope S, geometric features of the stream longitudinal profile of the drainage system, the location of the knickpoints and the amount of variant incision between upstream and downstream of the knickpoints are obtained. The results show that the bedrock channels on the northern slopes of the Zhongtiao Mountains has experienced accelerated incision in the longitudinal direction, and that the spatial variation of geomorphological parameters such as the normalized steepness index ksn, slope S and fluvial incision in the lateral direction is dominated by tectonic uplift, with high values in the Hangyang-Yongji section and decreasing in a segmental manner towards the west, which is consistent with the topographic relief of the Zhongtiao Mountains, but contradicts the high slip rate area and the Cenozoic subsidence centre(the Salt Lake). The geomorphic response to the slip rate is inconsistent with the topographic relief of the Zhongtiao Mountains, which is high in the west and low in the east. The high value area of geomorphic parameters reveals that the present active tectonic area of the Northern Zhongtiao Mountains Fault is located in the Hanyang-Yongji segment in the south, rather than the salt lake segment with high activity rate. The reason may be related to the migration of part of the activity of Huashan piedmont fault along the NE-trending hidden fault of Huayin Shouyang to the Hanyang Yongji segment of Zhongtiao Mountains. It suggests that the tectonic activity center of the Northern Zhongtiao Mountains Fault moves westward. Compared with the structural deformation caused by the change of sedimentary center, the time scale of river geomorphology response to structural deformation is shorter, and the landform is transformed most rapidly, which leads to the inconsistency between the geomorphological parameters and structural activities of the fault at the Northern Zhongtiao Mountains Fault. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE SLIP RATE OF THE NORTH ZHONGTIAO SHAN FAULT SINCE THE LATE MIDDLE PLEISTOCENE ZHANG Xiu-li, XIONG Jian-guo, ZHANG Pei-zhen, LIU Qing-ri, YAO Yong, ZHONG Yue-zhi, ZHANG Hui-ping, LI You-li SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1403-1420.   DOI: 10.3969/j.issn.0253-4967.2022.06.004 Abstract （379）   HTML （34）    PDF（pc） （9391KB）（163）       Knowledge map    Save Slip rate is an important parameter for the quantitative study of active fault and can be used to reflect the mode and intensity of fault activity. However, the selection of geomorphic surface, the acquisition of displacements, and the limitation of chronologic methods result in challenges to constrain the slip rate. A series of boreholes and geochronology studies revealed a continuous sedimentary sequence of the Quaternary in the Yuncheng Basin in the southern Shanxi Graben System. Multiple late Quaternary river terraces have developed and been preserved in the northern piedmont of the Zhongtiao Shan. The activities of the north Zhongtiao Shan Fault resulted in the elevation difference between the strata in the Yuncheng Basin and the river terraces. In this study, we chose the geomorphic units of the Xiaolicun River and combined them with the results of boreholes in the Yuncheng Basin to constrain the slip rates of the north Zhongtiao Shan Fault since the Late Pleistocene. Based on field observation and remote sensing image interpretation, we established the distribution and sedimentary characteristics of four terraces and the latest alluvial fan of the Xiaolicun River. Two main faults(F1 and F2)and a series of fractures or branch faults have been identified in these sedimentary strata. The high-resolution DEM of the faulted landform of the Xiaolicun River was obtained using UAV photogrammetry technology. Combined with a stratigraphic outcrop survey, the landform and sedimentary section across the fault were constructed. The abandonment ages of the terraces T4, T3, T2, and T1 have been determined as(214.3±13.9)ka, (118.5±6.4)ka, (59.6±2.4)ka, and(10.9±0.5)ka by OSL dating, respectively. The chronological results of the AMS 14C dating show that the alluvial fan north of F2 was deposited at 35~1ka. Based on these results, this study established the relationship between the geomorphic evolution of the Xiaolicun River and the activities of the north Zhongtiao Shan Fault. Since the late Middle Pleistocene, F1 had been active, accompanied by the abandonment of the T4. At~120ka, the terrace T3 was formed, F1 was no longer active, but F2 began to be active and raise T3 and T4 in the footwall. Since then, the Xiaolicun River has undergone rapid incision and formed T2 and T1. The continuous activities of F2 maintained T4-T1 in an uplifted state and formed a series of fractures in the alluvial fan. Based on this evolutionary relationship, T4, T3 and their corresponding strata in the boreholes of the Yuncheng Basin were used to constrain the slip rate of the north Zhongtiao Shan Fault in this study. After determining the depth in boreholes corresponding to the abandoned ages of T4 and T3, subtracting the influence of the surface slope and the activities of the southern Salty Lake Fault, and considering the depth error caused by climate change, the vertical displacements of the north Zhongtiao Shan Fault since the two periods were obtained with the vertical slip rate of(0.31±0.05)mm/a and(0.34±0.04)mm/a, respectively. Our results indicate that the slip rates of the north Zhongtiao Shan Fault since the late Middle Pleistocene are greater than those since the Late Pliocene and Quaternary. Table and Figures | Reference | Related Articles | Metrics

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RELIABILITY EVALUATION OF QUARTZ ESR DATING METHOD ON EARLY PLEISTOCENE SEDIMENT: A CASE STUDY OF JINGYUAN SECTION WEI Chuan-yi, YIN Gong-ming, WANG Xu-long, WANG Duo, JI Hao, LIU Chun-ru, LI Xin-xiu SEISMOLOGY AND GEOLOGY    2023, 45 (5): 1041-1056.   DOI: 10.3969/j.issn.0253-4967.2023.05.001 Abstract （193）   HTML （11）    PDF（pc） （4654KB）（161）       Knowledge map    Save As the most recent period of the geological record, the Quaternary climate change, tectonics and river drainage evolution have been well recorded by Quaternary sediment. Establishing the timing of these geological changes, and of their effects on the earth's environment, is a key element in Quaternary research. Because of dating range limit of quartz OSL dating and 14C dating, lacking of tephra for K-Ar dating, and strict restrictions for 26Al/10Be cosmogenic nuclide dating, the samples older than 200ka were critical but difficult in Quaternary dating, while electron spin resonance(ESR)dating method could provide absolute age for late Pliocene and Pleistocene samples. Previous studies show that quartz Al center and Ti-Li center are the most suitable signals for sediment ESR dating, and have been successfully applied into middle-late Pleistocene sediment dating. However, the application of those two centers ESR chronology into early Pleistocene or pre-Quaternary sediment remains confusion. In this study, early Pleistocene Jingyuan gravel layer sediment deposited at Yellow river were collected for ESR dating. The results of comprehensive comparative analysis of high resolution magneto-stratigraphy and deep-sea oxygen isotope curve of loess-paleosol sequences and high credible 26Al/10Be cosmogenic nuclide dating age make the Jingyuan gravel layer as the ideal material to evaluate the dating range, especially lower dating range, of the quartz Ti-Li center and Al center, respectively. The results show that: (1)The quartz Ti-Li center and Al center signal intensity of Jingyuan gravel layer was not saturated within 11 000Gy and 130 00Gy additional gamma ray dose, respectively; combined with the long thermal lifetimes of the quartz Ti-Li center(8×106a)and Al center(7.4×109a), guarantee the ESR dating range for million years. (2)The single saturation exponential function and “EXP+LIN” functions could provide more accuracy fitting result of equivalent dose of quartz Ti-Li center and Al center, respectively, and the fitting goodness is greater than 0.98. (3)The average ESR dating results of quartz Ti-Li center and Al center of Jingyuan gravel layer is~(1.67±0.15)Ma and~(1.65±0.69)Ma, respectively, which is consistent with the previously well-known age within the error range. To better understand the lower dating limit of the quartz ESR dating method, based on the previous analysis of the ESR signal thermal stabilities, we discuss the maximum saturation of the ESR signals and ESR signals' sensitivity. Combined with the fitting goodness evaluation of various fitting functions, we propose that the quartz Ti-Li center and Al center ESR dating method could provide reliable chronological constrains on the sand lens of early Pleistocene gravel layer. The results of our study not only provide a solid theorical foundation for the application of quartz ESR dating method for late Pliocene and early Pleistocene fluvial sediments, but also demonstrate a typical practice example of the ESR method on dating late Cenozoic sediments. Table and Figures | Reference | Related Articles | Metrics

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THE QUATERNARY NORMAL FAULTING AND RECENT CO-SEISMIC SURFACE RUPTURE AND RELATED SEISMOLOGICAL SIGNIFICANCE ALONG THE ARU CO GRABEN SYSTEM IN NORTHERN NGARI, TIBET WU Zhong-hai, Baima Duoji, YE Qiang, HAN Shuai, SHI Ya-ran, Nima Ciren, GAO Yang SEISMOLOGY AND GEOLOGY    2023, 45 (1): 67-91.   DOI: 10.3969/j.issn.0253-4967.2023.01.004 Abstract （323）   HTML （38）    PDF（pc） （16718KB）（161）       Knowledge map    Save The Qinghai-Tibetan plateau, with an average altitude of about 5^{}000m, is one of the most intense regions of intraplate deformation in the globe during the Quaternary. However, the very weak field investigation of active faults and incomplete historical earthquake data in the northern Qinghai-Tibet Plateau limit the in-depth understanding of the deformation mechanism of active tectonics and the characteristics of related strong earthquakes in the Qinghai-Tibetan plateau. Based on the comprehensive geological, remote sensing, and seismic data, the active faults in northern Ngari are interpreted in detail, and the Quaternary activity of the normal faults along the western boundary of Kunchuke Co graben in the southern section of the Aru Co graben system, the newly discovered co-seismic surface ruptures, its magnitude and seismogenic time are analyzed. The newly active fault images show that high-density active fault system dominated by the near east-west extension deformation was developed in the north Ngari. The Quaternary active fault system mainly includes near north-south normal faults and the conjugated strike-slip faults composed of the NW and NE strike-slip faults. The density of the normal faults is significantly higher than that of the strike-slip faults in the region. Based on the comprehensive analysis of the Aruko graben system and the latest co-seismic surface rupture along the western boundary of Kunchuke Co Graben. We present two main conclusions. 1)The Aru Co graben system, with a total length of 210 to 220km, is one of the largest extensional fault depression structures in northern Ngari. The graben system contains four secondary graben and half-graben distributed in left-step echelon distribution from south to north and shows obvious segmented activity characteristics. Meima Co-Aru Co graben is the most intense extensional deformation section along the Aru Co graben system during the Quaternary period. The left echelon pattern of the secondary graben in the graben system indicates that there is a right-lateral shear deformation component along the NW-trending graben system in the region. 2)The newly discovered co-seismic surface ruptures along the boundary fault of the western margin of Kunchuke Co Graben in the southern section of the Aru Co graben are typical normal fault-type ruptures. The surface rupture is distributed along the NNW-trending, with an outcrop length of nearly 400m, a maximum vertical displacement of about 0.8m, and an average vertical displacement of about 0.30.4m. Comprehensive historical earthquake records, the freshness of co-seismic surface ruptures, and the magnitude results based on the classic “surface displacement and magnitude” statistical formula, we concluded that the Kunchuke Co surface rupture should be a result of the 1955 MW6.5 earthquake event, which epicenter of the instrument was located in eastern Nawu Co of Gègyai county, with a focal depth of 35km and small length and displacement. The deep focal depth is a major cause of lead to the co-seismic surface rupture is obviously small-scale. This small-scale surface rupture event on active faults suggests that irregular or random local fault rupture behavior should be paid attention to in the study of the earthquake recurrence model of active faults. Table and Figures | Reference | Related Articles | Metrics

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THE SURFACE RUPTURE CHARACTERISTICS BASED ON THE GF-7 IMAGES INTERPRETATION AND THE FIELD INVESTIGA-TION OF THE 2022 MENYUAN MS6.9 EARTHQUAKE WANG Liao, XIE Hong, YUAN Dao-yang, LI Zhi-min, XUE Shan-yu, SU Rui-huan, WEN Ya-meng, SU Qi SEISMOLOGY AND GEOLOGY    2023, 45 (2): 401-421.   DOI: 10.3969/j.issn.0253-4967.2023.02.006 Abstract （168）   HTML （13）    PDF（pc） （22292KB）（160）       Knowledge map    Save On January 8th, 2022, an MS6.9 earthquake occurred around Menyuan County(37.77°N, 101.26°E), Qinghai Province. The epicenter is located in the northeastern part of the Tibetan plateau, where the western section of the Lenglongling Fault meets the eastern section of the Tolaishan Fault. In order to know the spatial distribution of coseismic surface rupture zone as soon as possible, and determine the seismogenic structure, the post-earthquake GF-7 remote sensing images of the Menyuan MS6.9 earthquake were analyzed. Moreover, combining the interpretation of the GF-7 images and the field investigation, the distribution of the co-seismic surface rupture was determined and the typical coseismic landforms, and the image recognition features of various co-seismic landforms are interpreted and summarized. The results show that the earthquake produced two major surface rupture zones with a left-stepped oblique spatial arrangement. The main northern branch rupture distributes on the west side of the Lenglongling Fault, with a length of about 22km and a strike of 100°N~120°E, the secondary rupture of the southern branch distributes along the eastern section of the Tuolaishan Fault, with a length of about 4km and a strike of N90°E. The total length of the two rupture zones is about 26km. Along the rupture zones, a series of typical left-lateral strike-slip coseismic landforms were formed, such as tensional fractures, tensional-shear fractures, pressure ridges, pressure bulges, left-lateral strike-slip gullies, as well as left-lateral strike-slip roadbeds, etc. We divided the surface rupture into six segments to conduct detailed observation and analysis, that is, the west of Daohe segment, Liuhuanggou segment, Honggou segment, Yongan River segment and Yikeshugou segment, from west to east among the main rupture zone of the north branch, as well as the secondary rupture zone of the south branch. In general, each co-seismic landform has its distinctive image characteristics, and we obtained them from the interpretation and summarization of the GF-7 images. The shear fractures located at the two ends of the main rupture and in the areas where the surface rupture is weak are zigzaggy on the remote sensing images, while the shear fractures located in the areas where the surface rupture is intense are shown as dark, wide and continuously smooth stripes; thrust scarps are represented on remote sensing images as shaded, narrow and slightly curved strips; the pressure ridges and pressure bulges exhibit black elliptical feature on the images that are parallel or at a smaller angle to the main rupture; tensional-shear fractures are displayed as black strips arranged in en echelon with a 30°~45° intersection angle with the main shear rupture, and their linear features are not as straight as those of shear ruptures yet are still distinct; the coseismic scarps formed on the ice are manifested in the images as traction bend and texture change. Based on the GF-7 images, the cumulative dislocations of typical sinistral landforms along the co-seismic surface rupture on Lenglongling Fault are interpreted and futher compared with the previous study. This is the first time of application of GF-7 to the strong earthquake geohazards monitoring since it was officially launched in August 2020. From this study, it can be seen that with its high resolution, GF-7 can be used to accurately identify faulted features. Not only it could provide information of the geometric roughness, complexity and segmentation of the fracture, but also can record clear dislocations of the landforms. The study of the GF-7 images in the 2022 Menyuan earthquake has showed that the GF-7 images can provide strong data support for the geology and geological hazard studies. Table and Figures | Reference | Related Articles | Metrics

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MORPHOLOGIC DATING OF SCARP MORPHOLOGY BASED ON DIFFUSION EQUATION: A REVIEW XU Jian-hong, CHEN Jie, WEI Zhan-yu, LI Tao SEISMOLOGY AND GEOLOGY    2023, 45 (4): 811-832.   DOI: 10.3969/j.issn.0253-4967.2023.04.001 Abstract （241）   HTML （30）    PDF（pc） （5260KB）（156）       Knowledge map    Save A scarp is a common step-like landform in nature, which consists of a gently sloping plane connected to the upper and lower geomorphic surfaces of differing elevations. Common scarps include fault scarps, terrace scarps, lake shoreline scarps, shoreline scarps, volcanic ash cinder cones, etc. Scarps are often used as strain markers because of their linear characteristics and are favored in the study of active tectonics. However, it is difficult to directly constrain their ages. Instead, they are usually constrained by the ages of the upper and lower geomorphic surfaces. The scarp developed in loose deposits is controlled by a long process of low-energy degradation after a short collapse. This process can be modeled by the diffusion equation because the process can be considered as a slope process under the transport-limited condition. Under this condition, the slope can provide enough loose material for transport, that is, the material transport capacity is less than the material supply capacity. If process assumptions are sufficiently valid and rate constraints can be calibrated independently, the true age of scarps can be obtained. This method is called morphologic dating. This method has been included in many textbooks published overseas, but there have very little research on this method in China. Both linear and nonlinear models have been developed to describe scarp degradation. Linear diffusion models assume that the diffusion coefficient is a constant, whereas nonlinear transport models generally define the diffusion coefficient as a nonlinear function related to the topographic gradient. Compared to the linear transport models, nonlinear transport models can better explain the phenomenon of rapidly increasing deposition flux as the gradient approaches a critical value. In this paper, we review the study history of scarp degradation analysis and the concept model of scarp degradation. We focus on the establishment of the nonlinear model, the role of the different parameters in profile evolution, determining the best-fit age using a full-scarp nonlinear modeling procedure, and so on. Furthermore, we introduce the model of the nonlinear age chart, including the effect of far-field slope on morphologic dating of scarp-like landforms and two examples of the application of the chart, which shows that this method can correctly evaluate the ages of single-event scarps. Finally, we discuss the extension of the concept and method of the scarp degradation model, the applicability of the model, and repeated fault scarp morphological analysis. For nonlinear diffusion models, in addition to n equal to 2, two parameters (critical gradient (Sc) and diffusion constant (k)) need to be constrained. The critical gradient can be obtained from the young scarps in the study area, which roughly represents the initial state of scarp evolution, typically 0.6 to 0.7(30° to 35°). The diffusion constant needs to be characterized by a known age scarp. The slopes of the upper and lower geomorphic surfaces have an obvious influence on the morphology of a degraded scarp. These discussions indicate that both linear and nonlinear models can be used for the degradation analysis of single-event scarps, but a nonlinear diffusion model is recommended for young single-event scarps. The constant slip rate nonlinear model can be used to simulate the evolution history of<10ka high-slip rate active fault scarp. The multiple-event scarp model requires careful evaluation of the fault location and the amount of displacement per event. There are several assumptions in the scarp topography diffusion modeling, which require practice to verify its reliability. With advances in surveying technology, it is now possible to rapidly obtain high-resolution terrain data over broad areas from which numerous topographic profiles can be efficiently extracted. This provides a broad application prospect for scarp degradation analysis and morphologic dating. Table and Figures | Reference | Related Articles | Metrics

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NEW ACTIVITY CHARACTERISTICS IN THE CHISHAN SECTION OF TAN-LU FAULT ZONE IN HOLOCENE ZHENG Hai-gang, YAO Da-quan, ZHAO Peng, YANG Yuan-yuan, HUANG Jin-shui SEISMOLOGY AND GEOLOGY    2023, 45 (1): 127-138.   DOI: 10.3969/j.issn.0253-4967.2023.01.007 Abstract （281）   HTML （28）    PDF（pc） （10175KB）（155）       Knowledge map    Save The Chishan section of Tan-Lu fault zone is located in Sixian County, northern Anhui Province. Research on the characteristics of Quaternary fault activity of this section began in the 1990s, which includes microgeomorphology survey, trench excavation, dating sample collection and measurement, and so on. Through these studies, many valuable data and results were accumulated, which laid a good foundation for the current research. Based on the field geological survey and previous studies, two geological trenches were excavated, which are named trench XJ1 and XJ2 respectively. Among them, very rich remains of ancient earthquakes were found in trench XJ1 and analyzed as major contents in this paper, and few relics of ancient earthquake were found in trench XJ2, which are not involved in this paper. In the trench XJ1, ten strata units were revealed, labeled as U1 to U10 from old to young, respectively. Layer U1 is the Cretaceous sandstone with a thickness about 0.5~1.0m, lying on the bottom of the west wall of the trench. Layer U2 is yellowish brown clay with a thickness of 1~2.5m, located at the bottom of the eastern side of trench profile. One OSL sample is collected in the middle of this layer with an age more than 150k {\mathrm{a}}^{}BP, which indicates the layer was deposited before the Mid Pleistocene. Layer U3 is purple clay-sand, which is wide at the bottom around 6.5m and narrow at the top around 2.5m, and the top extends about 7m continuously from west to east. Layer U4 is motley gravel with a thickness about 2.0~2.5m, which is below layer U9 and above layer U4 on the west side of the trench wall. Layer U5 is gravel containing a lot of clay and a few of sandstone clumps, wide at the top about 3m and narrow at the bottom about 2m. Layer U6 is light green gravel containing some sand and clay, thick in the west about 0.8m and thin in the east about 0.2m, extending around 7m discontinuously from west to east. Layer U7 is grayish white gravel with sand and clay, thick in the west around 1.0m and thin in the east around 0.2m, extending about 5m continuously from west to east. Layer U8 is yellow clay with a thickness of 0.5~2.0m, located below layer U9 and above U7. One peat sample was taken from the top of the layer and the age of this sample is 21.57~21.22k {\mathrm{a}}^{}BP measured by Beta Analytic Inc in the United States, which indicates this layer was deposited in Late Epipleistocene. Layer U9 is black clay with a thickness of 0.5~1.5m, which is located above Layer U4, U5, U7 and U8 and is the latest disturbed layer in the trench. One peat sample was taken from the bottom of this layer and the age of this sample is 11.10~10.75k {\mathrm{a}}^{}BP measured by Beta Analytic Inc in the United States, which indicates this layer was deposited in the early Holocene. Layer U10 is the cultivation layer with a thickness of 0.2~0.5m, located on the topmost of the trench wall. Three faults were revealed in these layers, named as F1 and F2 and F3 respectively from east to west. Three paleoseismic events were identified, which are labeled as E1 and E2 and E3 respectively from old to new. The E1 represents a thrust activity of fault F1. After the deposition of layers U5, U3 and U2 finished, the hanging wall U5 of fault F1 thrust upward above the footwall U8, and the soft layer U3 in between was squeezed and rubbed upward, forming lenticles in the layer, which indicates the movement direction of the hanging wall of F1 is thrust upward. A compressional overfall scarp was formed by this event, then the layer U6 was deposited on the east side of the scarp, whose age is not measured. But the dating of layer U2 beneath the fault F1 yields an age before Mid Pleistocene, which constrains the lower limit age of E1 to be after Mid Pleistocene. The E2 represents a thrust faulting of fault F2. After the deposition of layer U6, a new thrust faulting occurred on fault F2, which cut through layer U5 and formed a thrust fault scarp. Later, U7 and U8 were deposited on the east of the scarp. The layer U7 is gravel, whose age is not measured, but the layer U8 is dated as the Late Epipleistocene, which constrains the upper limit age of events E1 and E2 to be after Late Epipleistocene. The E3 represents a strike-slip normal faulting of Fault F3, which faulted the layer U3. According to the age of the layer U3, we can constrain the lower limit age of E3 to be the Early Holocene, which indicates that the Chishan section of the Tan-Lu fault zone is still active after the Early Holocene. To sum up, two geological trenches were excavated at the Chishan section of Tan-Lu fault zone, named as trench XJ1 and XJ2 respectively, and three main faults were revealed on the wall of trench XJ1, named as F1, F2 and F3 from east to west, and three paleoseismic events were identified, which are labeled as E1 and E2 and E3 respectively from old to new. The latest ancient seismic event faulted the Early Holocene layer, indicating the Chishan section of the Tan-Lu fault zone is still active after the Late Holocene, and the latest activity is of strike-slip normal faulting, which provides new evidence for the presence of Holocene activity of this fault section and new information for long-term seismic risk assessment in this area. Table and Figures | Reference | Related Articles | Metrics

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STATUS OF RESEARCH AND OBSERVATION ON UNDERGROUND FLUID HYDROGEN IN SEISMIC FAULT ZONES IN CHINA JIANG Yu-han, WANG Zi-si, LIU Jia-qi, LIANG Hui, ZHOU Qi-chao, GAO Xiao-qi SEISMOLOGY AND GEOLOGY    2023, 45 (3): 622-637.   DOI: 10.3969/j.issn.0253-4967.2023.03.002 Abstract （198）   HTML （25）    PDF（pc） （2106KB）（154）       Knowledge map    Save Large-scale observation network has been set up in China, including the observations of groundwater dynamics, geothermal water, and geochemical parameters, and long-term observation data has been obtained for underground fluids. Hydrogen observation is considered to be one of the methods that are most likely to make a breakthrough in the aspect of earthquake precursor monitoring and prediction, thus, plays an important role in earthquake monitoring and forecast in China. Many scholars have carried out research on the relationship about hydrogen and earthquake precursors, and proved that abnormal hydrogen concentrations are related to and have certain correlations earthquake activities. The main objects of hydrogen observation in China include the escaping gas from fault soil and the escaping gas from deep wells and hot springs near the fault. Different analytical methods are used for different types of hydrogen, and the main methods include gas chromatograph analysis and digital high-precision hydrogen analyzer analysis. Through years of observation practice, a large number of typical examples have been obtained in China. The relationship between the abnormal hydrogen concentration and the earthquake has a correspondence. The main manifestation is that the hydrogen concentration increases several times or even tens or hundreds of times in a few months or a few days before the earthquake. It is mainly divided into two cases: First, it rises rapidly to several times in a short time before the earthquake. The concentration reaches about hundreds of times the background value in more than ten to a few days immediately before the earthquake, and then the earthquake occurs. The concentration quickly declines and restores the background value after the earthquake. Second, the hydrogen concentration continues to increase in fluctuation, and decreases after reaching the maximum value, then, the earthquake occurs after recovery. This kind of anomaly is short in time, mostly, they are imminent or medium and short-term abnormalities. Therefore, the hydrogen response to the earthquake precursor is an important short-imminent earthquake prediction indicator, and can be used as an important approach to explore the short-impending earthquake prediction. The hydrogen in the crust mainly comes from biochemical and chemical actions. The hydrogen on the surface layer of the crust is mainly produced by microbial decomposition of organic matter and mineral salts. It is regularly symbiotic with gases such as methane and carbon dioxide. The hydrogen in the crustal fault belts, especially in the active fault zones, also comes from the failure and deformation of rock. The formation mechanism of hydrogen in the crust can be summarized into 3 categories: 1)Under normal circumstances, the hydrogen content is very low, and most of them exist in the pores of the rock and soil layer in a free state, or are adsorbed on the surface of the rock. When the external conditions remain unchanged, the gas is in a balanced state; when the environment changes, especially the underground stress changes, the cracks develop continuously under the action of tectonic stress, resulting in interconnecting each other, and subsequently, the deep hydrogen also changes and emits to the ground surface, including the imminent rupture stage in the earthquake preparation and rock oscillation; 2)The chemical reactions occur between the crushed rock's fine particles and water, generating hydrogen; 3)The temperature gradient causes the hydrogen attached in the crack to escape. In short, hydrogen is a better method for studying earthquake reflecting ability among the underground fluid observation methods. Representative earthquake cases are obtained from observations of both dissolved hydrogen in the water or soil hydrogen. This observation item plays an important role and has practical significance in the geochemical observation means. In the observation of earthquake underground fluids, hydrogen observations can provide data support for future earthquake risk zoning and earthquake tendency tracking and analysis. Table and Figures | Reference | Related Articles | Metrics