Most Download articles

Published in last 1 year | In last 2 years| In last 3 years| All| Most Downloaded in Recent Month| Most Downloaded in Recent Year|

Most Downloaded in Recent Month

Please wait a minute...


For Selected: Download Citations EndNote Ris BibTeX Toggle Thumbnails

Select

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 （62）   HTML （11）    PDF（pc） （9173KB）（48）       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

Select

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 （343）   HTML （19）    PDF（pc） （16086KB）（186）       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

Select

CRUSTAL S-WAVE VELOCITY STRUCTURE BENEATH THE XIAO-JIANG FAULT ZONE AND ADJACENT REGIONS REVEALED BY TWO-STEP INVERSION METHOD OF RECEIVER FUNCTIONS YANG Jian-wen, JIN Ming-pei, CHA Wen-jian, ZHANG Tian-ji, YE Beng SEISMOLOGY AND GEOLOGY    2023, 45 (1): 190-207.   DOI: 10.3969/j.issn.0253-4967.2023.01.011 Abstract （45）   HTML （9）    PDF（pc） （10460KB）（41）       Knowledge map    Save In the past few decades, a large number of geophysical explorations were carried out in the Xiaojiang fault zone and adjacent areas, mainly including GPS, seismic geology, fluid geochemistry, seismicity, historical earthquakes and coseismic displacement of large earthquakes, etc. The results of these studies helped us have a better understanding of the fault structure characteristics, movement attributes, seismogenic environment and dynamic mechanism of the Xiaojiang fault zone. In terms of deep structure, the existing researches are limited by factors such as the density of observation stations, and most studies focused on the structural background on the regional scale, and few are specifically on this fault zone. The implementation of Phase I of the China Earthquake Science Array(ChinArray)detection project provides a good data basis for the study of the fault structure in Yunnan. It is of great practical significance for earthquake prevention and disaster mitigation to carry out deep structural detection of the Xiaojiang fault zone and clarify the fine crustal structure of the fault and its adjacent areas. S-wave velocity is an important parameter to determine the crustal structure, physical state difference and tectonic evolution process. Extracting the P-wave receiver function from teleseismic body-wave waveform data and inverting it is one of the important methods to obtain the crustal S-wave velocity structure at present. The traditional receiver function S-wave velocity structure inversion relies heavily on the selection of the initial model, which results in strong non-uniqueness inversion results. The two-step inversion method, which takes into account the low and high frequency receiver functions at the same time, effectively suppresses the dependence of the inversion process on the initial model, and improves the reliability of the inversion results. Based on the three-component waveform data of 238 teleseismic events with epicentral distances ranging from 30°~90° and magnitude M≥5.8 recorded by 48 broadband seismic stations in the Xiaojiang fault zone and adjacent areas from September 2, 2011 to January 16, 2014, this paper calculates the low-frequency(α=1.0)and high-frequency(α=2.5)radial P receiver functions, respectively. Then, on this basis, the S-wave velocity structure below each station is inverted using the two-step inversion method and Bootstrap resampling technique and the deep crustal structure of the Xiaojiang fault zone and its adjacent areas is studied. The following conclusions are drawn:= (1)The crustal S-wave velocity in the study area is obviously non-uniform in both lateral and vertical directions. The overall distribution is as follows: In the near surface, there is a low-velocity layer about 2~4km thick, which may be related to the distribution of shallow sedimentary rocks or Cenozoic soft overburden; The S-wave velocity in the middle and upper crust is alternately distributed with high and low velocity; There is an obvious low-velocity layer in the depth range of 20~35km, mainly intermittently distributed in the Sichuan-Yunnan diamond block west of the Xiaojiang Fault and the Indosinian block south of the Honghe Fault; Besides, there is also local distribution near the Shizong-Mile Fault. (2)The low-velocity layer in the middle and north segments of the Xiaojiang fault zone are relatively developed, and it is most prominent in the middle segment, with a maximum thickness of about 28km. There is an obvious high-velocity zone in the depth range of 15~25km in the southern segment. (3)The Poisson’s ratio in the study area is generally low(average 0.24), unevenly distributed, and has drastic lateral changes. The Poisson’s ratio in the Xiaojiang fault zone generally has a segmental feature of higher in the northern segment, the southern segment coming second, and lower in the middle segment. The corresponding relationship between the distribution of low velocity in the crust and Poisson’s ratio in the study area is not obvious, and most of the low velocity layers seem to lack the conditions for partial melting. The differences and inconsistencies in the geophysical results indicate that the deformation evolution mechanism and physical properties of the low velocity layers in the crust are relatively complex. Table and Figures | Reference | Related Articles | Metrics

Select

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 （223）   HTML （35）    PDF（pc） （7558KB）（116）       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

Select

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 （50）   HTML （8）    PDF（pc） （5275KB）（39）       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

Select

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 （39）   HTML （15）    PDF（pc） （11448KB）（39）       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

Select

THE COSEISMIC RUPTURE MODEL AND STRESS CHANGE OF THE 2022 MENYUAN MW6.7 EARTHQUAKE YU Shu-yuan, HUANG Xian-liang, ZHENG Hai-gang, LI Ling-li, LUO Jia-ji, DING Juan, FAN Xiao-ran SEISMOLOGY AND GEOLOGY    2023, 45 (1): 286-303.   DOI: 10.3969/j.issn.0253-4967.2023.01.016 Abstract （54）   HTML （7）    PDF（pc） （11147KB）（35）       Knowledge map    Save On January 8, 2022, an earthquake of MW6.7 occurred in Menyuan County, Qinghai Province. The epicenter of the earthquake is located in the middle eastern section of the Qilian Mountains seismic belt on the northeast edge of the Qinghai-Tibet Plateau. Under the northward push by the Qinghai-Tibet Plateau plate, and the push and subduction in the northeast direction of the Qilian Mountains, and also blocked by the Alxa block and affected by the push in the southwest direction of the Longshou Mountains uplift area at its front edge, a ramp structural pattern of compressive depressions was formed in the Hexi Corridor basins area. As a result, most of the active faults in this area are mainly NW-trending, and the active features are mostly characterized by compressional thrusting and strike slip. This paper reconstructs the coseismic deformation field of Menyuan earthquake through the European Space Agency Sentinel-1A C-band radar satellite data and D-InSAR technology, determines the geometric characteristics of the seismogenic fault through the inversion method of optimum fault slip distribution, and determines the seismogenic fault of this earthquake. The results show that the deformation range of the radar line of sight is -0.42~0.7m for the ascending track deformation field and -0.63~0.72m for the descending track deformation field, and the maximum deformation locates in the Lenglongling section. The data of ascending and descending tracks show that there are two obvious deformation regions with a butterfly-like stripe pattern. The sign of LOS deformation variable observed in InSAR deformation field of ascending and descending orbits in the same area is opposite. Combined with the flight direction of ascending and descending satellites, it is determined that the motion of seismogenic fault is mainly left-lateral strike slip. Among them, the Lenglongling Fault and Tolaishan Fault pass through the fracture surface revealed by InSAR deformation field, which means that the above fault is highly likely to be the seismogenic fault of the Menyuan earthquake in 2022. At the same time, the SE-trending Lenglongling Fault on the east side passes through the fracture surface, with a surface fracture length of about 20km. The EW-trending Tolaishan Fault on the west side also passes through the fracture surface, with a fracture length of about 5km. And then, according to the field geological survey results of this earthquake, taking the InSAR coseismic deformation field data as constraints and based on Okada elastic dislocation model, the geometric structure of the seismogenic fault and the fine slip distribution characteristics of the fracture surface are determined. The inversion results reveal that there are two slip regions, of which the slip is mainly concentrated in the Lenglongling fault section, with a maximum left-lateral slip of 3.66m and a maximum slip depth of 5km. There is also a maximum sinistral slip of 1.95m occurring at a depth of 5km in the Tolaishan Fault. It is inferred that the seismogenic fault is the western section of Lenglongling Fault which also ruptured the Tolaishan Fault on its west. On this basis, Coulomb33 software is used to calculate the static Coulomb stress changes generated by the Menyuan earthquake at different depths(5km, 10km, 15km and 20km). The Coulomb stress change image within 300km of the epicenter shows a typical four-quadrant distribution characteristic. There are four fan-shaped stress increase and decrease areas at 5km underground. The area with the largest increase in stress is near the Beiyuan Fault of Tuole Mountain in the west of the epicenter of Menyuan earthquake. The increase of stress is over 0.03MPa, greater than the trigger threshold of 0.01MPa. The stress increase coverage area in the south of the epicenter further expanded, with a stress increase of more than 0.03MPa, inducing many aftershocks distributed linearly in the NWW direction along the epicenter. According to the overall analysis, most of the subsequent earthquakes in Menyuan occur at a depth of 10~12km, which is in good agreement with the stress increase area at the corresponding depth. At the same time, for the NW-SE area and NE-SW end of the rupture in the epicenter, the area with ΔCFS≥0.01MPa is worthy of attention for the subsequent risk. Finally, based on the GPS velocity field relative to the Ordos block, it is analyzed that the Lenglongling area moves in the NE direction relative to the Ordos block as a whole, the GPS velocity vector north of the Lenglongling Fault decreases, and the movement direction turns to NNW. Using GPS velocity field to calculate the principal strain rate, shear strain rate, surface strain rate and principal compressive stress in Lenglongling area, it is shown that there is a significant high value area of surface strain in Lenglongling area. The principal strain rate is NE compression, and the peak value of shear strain rate is located on the north side of Lenglongling Fault and the east section of Minle-Damaying Fault. Its strain accumulation indicates that the area is still in a high stress state, and the seismic activity may continue to be strong in the future. The regional surface strain rates show obvious compression characteristics, and the principal strain rates show NE-SW compression and NW-SE extension. Overall, the source area of the Menyuan earthquake is still under the push in the NNE direction of the eastern Himalaya syntaxis of the Indian plate. It can also be seen that the Menyuan earthquake occurred in the high value area of the maximum shear strain rate and the compression area of the surface strain. The occurrence of the Menyuan earthquake in the Lenglongling area of the North Qilian Mountains on the northeast edge of the Qinghai-Tibet Plateau and its current high stress accumulation indicate that the Lenglongling Fault may still be active today. On this basis, the seismogenic structural characteristics and seismogenic relationships of the two Menyuan earthquakes in 2016 and 2022 are further discussed. The 2016 Menyuan earthquake is located on the extension line of the Minle-Damaying Fault. The seismogenic fault is a SW-trending thrust fault. The fault extends in NW-SE direction on the surface along the front of the mountain, and its deep part may converge to the detachment layer at the bottom of the Qilian Mountains together with the Lenglongling Fault. The fault has the potential to generate destructive earthquakes. The 2016 MW5.9 Menyuan earthquake and the 2022 MW6.7 Menyuan earthquake have different seismogenic mechanisms, but the seismogenic faults all belong to the North Qilian Mountains active fault zone, most of which control the boundary of the Neogene basins. Both earthquakes are the local adjustment of stress accumulation in the region as a whole, and the expression of the northeastward pushing of the Qinghai Tibet Plateau. Some scholars believe that Lenglongling fault zone, Jinqianghe Fault, Maomaoshan fault zone and Laohushan Fault jointly constitute the “Tianzhu earthquake gap”. The occurrence of three Menyuan earthquakes in 1986, 2016 and 2022 has drawn continuous attention to the fault activity and seismic risk of this area. Table and Figures | Reference | Related Articles | Metrics

Select

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 （165）   HTML （18）    PDF（pc） （7110KB）（114）       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

Select

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 （37）   HTML （11）    PDF（pc） （9154KB）（34）       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

Select

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 （41）   HTML （18）    PDF（pc） （16718KB）（32）       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

Select

COMPREHENSIVE ANALYSIS OF GRAVITY AND CRUSTAL DEFORMATION OF JIASHI MS6.4 EARTHQUAKE IN 2020 ZHU Zhi-guo, ZHU Yi-qing, WANG Dong-zhen, HUSAN Irxat SEISMOLOGY AND GEOLOGY    2023, 45 (1): 269-285.   DOI: 10.3969/j.issn.0253-4967.2023.01.015 Abstract （36）   HTML （6）    PDF（pc） （9171KB）（31）       Knowledge map    Save The intracontinental orogeny of Tianshan Mountains has led to strong tectonic activity in the southern Tianshan seismic belt, and strong earthquakes occur frequently at the junction of basins and mountains. On January 19, 2020, an MS6.4 earthquake occurred in Jiashi County, Xinjiang Uygur Autonomous Region. This earthquake is of north-dipping thrust motion with a small amount of strike-slip component. The seismogenic structure of the earthquake is the Keping Fault on the southernmost edge of the Keping Tage thrust nappe in the South Tianshan Mountains. The Keping Fault has a total length of about 460km. The overall strike of the fault is near EW, dipping northwest, and the dip angle is more than 45°. It is the boundary fault between Tianshan Mountains and Tarim Basin in Southwest China. The Jiashi MS6.4 earthquake is an important earthquake, which broke the 17 years quiet period of MS6.0 earthquakes since 2003. It is of great value for study on the evolution of regional tectonic deformation. The process of earthquake preparation will be accompanied by changes in geophysical field. Comprehensive analysis of geophysical observation data before and after earthquakes has great practical significance for geodynamics research and identification of earthquake precursor anomaly information. The epicenter of Jiashi earthquake is located in the monitoring area of the “Kashi-Jiashi” mobile gravity observation network and the “Crustal Movement Observation Network of China” GNSS observation. In this paper, the mobile gravity and GNSS observation data from 2015 to 2021 are selected. The mobile gravity observation network uses absolute gravity point constraint to carry out the classical adjustment calculation of the whole network, and then obtains the gravity field change image; The GNSS data are solved by GAMIT/GLOBK software to obtain the movement rate of the study area, and the horizontal apparent strain field distribution is obtained by means of the partial derivative relationship between displacement and strain. By analyzing the dynamic change characteristics of gravity field, velocity field and strain field in the seismogenic area, the relationship between the change of gravity field and GNSS deformation field and the seismogenic process of Jiashi MS6.4 earthquake is comprehensively discussed. The results show that: 1)The time-varying images of the gravity field on the time scale of one year better reflect the evolution process of the regional gravity field system near the Jiashi MS6.4 earthquake. The “0” contour of gravity change and its four quadrant characteristics provide useful references for earthquake prediction. 2)The cumulative change of gravity field reflects that the change of regional gravity field before the Jiashi MS6.4 earthquake was controlled by regional large faults. A series of medium and strong earthquakes in the study area occurred in the process of gravity reverse change. The characteristics of high gradient belt of gravity change are closely related to earthquake occurrence. According to the gravity cumulative change and time-varying image, it is speculated that this tectonic activity may have started in 2018. 3)Strong earthquakes are likely to occur on tectonic active fault zones with significant gravity changes. The Keping earthquake of M=6.4 in 2020 occurred in the area where the high gradient zone of gravity changes turns, which is also the transition zone of surface compressibility changes. The variation process of regional strain field corresponds to the positive and negative cumulative changes of the regional gravity field. Table and Figures | Reference | Related Articles | Metrics

Select

RESEARCH ON SEMI-AUTOMATIC EXTRACTION METHOD OF SEISMIC SURFACE RUPTURES BASED ON HIGH-RESOLUTION UAV IMAGE: TAKING THE 2021 MS7.4 MADUO EARTHQUAKE IN QINGHAI PROVINCE AS AN EXAMPLE LI Dong-chen, REN Jun-jie, ZHANG Zhi-wen, LIU Liang SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1484-1502.   DOI: 10.3969/j.issn.0253-4967.2022.06.008 Abstract （124）   HTML （14）    PDF（pc） （11560KB）（84）       Knowledge map    Save Field investigations of large earthquakes indicate that earthquakes with a magnitude greater than 6.5 often produce seismic surface rupture zones ranging from thousands of meters to tens of kilometers on the earth’s surface. The geometric structures of surface ruptures contain the kinematic characteristics of seismogenic structures, which can not only provide critical quantitative data for analyzing the spatial distribution law of co-seismic displacement of active faults and the width of active fault deformation zone, but also have an important significance for understanding the kinematic mechanism and deformation law of seismogenic faults. At present, the conventional methods to obtain earthquake surface ruptures mainly include the field geological survey and visual interpretation of the remote sensing image. Although these two methods can get the rough geometry of coseismic surface ruptures, they both have certain limitations. The reliability of the field geological survey method is high. However, intra-continental earthquakes often occur in places with complicated topography, and lots of sites are difficult to reach, leading to incomplete data and failure to draw detailed features of the fracture zone. Meanwhile, the field geological survey is often time-consuming and laborious. Although the visual interpretation of remoting sensing images can be used to interpret surface fractures in areas that cannot be reached by the geological field survey, the result accuracy is vulnerable to the impacts of interpreters’ experience. The whole process of interpretation is still time-consuming and labor-intensive and the extraction results are mostly linear surface ruptures, so it is difficult to accurately obtain fine features such as the width of the surface rupture zone. Therefore, the automatic extraction of fine structures of seismic surface ruptures, especially micro-rupture surfaces, is an urgent problem in active tectonic studies. The remote sensing images obtained through satellite platforms have low resolution and are susceptible to weather factors, and the extracted surface rupture fineness is not enough. The UAV platform, on the other hand, is low-cost to use, can fly at a low altitude, is not affected by clouds and fog, and can acquire images with a centimeter-level resolution, which provides conditions for extraction the fine structure of surface ruptures of large earthquakes. Thus, to solve the problem that it is difficult to obtain surface ruptures of large earthquakes quickly, this study proposes an object-oriented “Rough segmentation and Fine extraction” method based on object-oriented and color segmentation theories of color space, which realizes the semi-automatic extraction of features of seismic surface rupture zone. The processing workflow of the method is as follows: First, the original image is cropped by the custom irregular raster cropping method designed in this study to obtain ROI(the Region of Interest). Second, the color space of ROI is converted into HSV, and the HSV color space of ROI is segmented into surface rupture candidate area by using brightness and hue tone values. And then, the surface rupture candidate area is processed by expansion operation of binary mathematical morphology. Third, the surface rupture candidate area is transformed into a series of sub-area objects by the contour tracking method. Fourth, the surface rupture is refined using the spectral standard deviation, spectral mean and the length-width ratio of the smallest surrounding rectangle as characteristic parameters. Finally, the results are output as the vector surface of surface ruptures. The effectiveness of the proposed method is analyzed by taking the high-resolution UAV image data of the MS7.4 Maduo earthquake in Qinghai Province as an example. The results show that the proposed method can effectively remove the noises such as the river channel similar to the characteristics(i.e., the color and shape features)of the surface rupture and extract the delicate structures of the surface rupture zone quickly and accurately, except that several poor extraction results were caused by the limitation of image resolution and the destruction of surface rupture caused by river erosion. The extraction results are highly reliable and can be used to extract quantitative parameters of surface ruptures in large earthquakes. Thus, the semi-automatic extraction method of seismic surface ruptures established in this study can provide a feasible scheme for the rapid extraction of delicate structures from surface ruptures and analysis of surface deformation characteristics after a large earthquake. Table and Figures | Reference | Related Articles | Metrics

Select

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 （57）   HTML （17）    PDF（pc） （10175KB）（28）       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

Select

TYPICAL REMOTE SENSING IMAGES OF HOLOCENE FAULTS IN GAIZE PAN(I45)IN TIBET BAI Qilegeer, SHEN Jun, XIAO Chun, DAI Xun-ye SEISMOLOGY AND GEOLOGY    2023, 45 (1): 92-110.   DOI: 10.3969/j.issn.0253-4967.2023.01.005 Abstract （41）   HTML （14）    PDF（pc） （11318KB）（25）       Knowledge map    Save Active faults refer to faults that have been active since the late Quaternary(100000~12 0^{}000 years)which are the culprits of large earthquakes. They can be divided into Holocene faults and Late Pleistocene faults. The Holocene fault is the active fault that has displaced on or near the surface in the past 10000 years. The Active faults may cause seismic surface dislocation in the future, which will damage the project crossing the active fault. It is necessary to take measures to avoid or resist the fault. Therefore, finding out the distributions of active faults are the prerequisite for reducing earthquake disaster losses and disaster risks. We undertook the compilation of the 1︰1000000 seismotectonic map of Tibet in the first national comprehensive risk survey of natural disasters. The preparation of a seismotectonic map is to conduct detailed investigation and research on active faults within the research scope, including large-scale active faults with a strong earthquake-generating capacity, as well as small-scale and highly active faults. The Qinghai-Tibetan plateau is a typical strong earthquake-prone area with wide distribution, high frequency, high intensity and shallow source of seismicity. This study introduces the Holocene active faults in the modified scale(I45)of 1︰1000000 international standard topographic map. We use Satellite remote sensing images to determine the locations of the faults, identify their characteristics, and assess the ages of their latest activity and quantitative parameters such as intensity. Satellite remote sensing interpretation is the most important method to study active faults. This is especially true in the Qinghai-Tibetan plateau region, where active fault traces are clear and lack overlying Quaternary layers. High-resolution satellite remote sensing images can capture various tectonic and geomorphological phenomena formed by fault activity. In the study area, we interpreted Six Holocene active faults by using high-resolution satellite images, including the MargaiCaka fault, the Riganpeicuo fault, the Yibuchaka graben, the Qingwahu fault, the Dongcha fault, and the central part of Qixiangcuo fault. When analyzing each fault, typical images with evidence of active faults are intercepted, and the typical remote-sensing image features of active faults are summarized. It is clear that the typical remote sensing images of active faults are the remote sensing images which can reflect the dislocation of late Quaternary strata, geological bodies and geomorphic surfaces(unit). The latest active age, slipping senses and active intensity of above active faults in the area, as well as the overall tectonic pattern and seismic capacity of active structures in the area are discussed. The MargaiCaka fault in the north of the study area and the Riganpeicuo fault, the Qixiangcuo fault in the south are large-scale left-lateral strike-slip faults of NEE trending and have the capability of generating earthquakes of about magnitude 7.5. The NEE-trending Yibuchaka graben, the Qingwahu fault, and the NW-trending Dongcha fault in the central of the map unit have the capability of generating earthquakes of about magnitude 7. The above-mentioned faults reflect a special dynamic environment in which the area is squeezed in the north-south direction, and a V-shaped conjugate fault formed, making the plateau squeezed out to the east. Table and Figures | Reference | Related Articles | Metrics

Select

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 （193）   HTML （22）    PDF（pc） （9391KB）（84）       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

Select

THE STATIC COULOMB STRESS INFLUENCE OF THE MAINLING M6.9 EARTHQUAKE IN TIBET ON NOVEMBER 18, 2017 TO THE SUBSEQUENT EARTHQUAKES LI Zhen-yue, WAN Yong-ge, JIN Zhi-tong, YANG Fan, HU Xiao-hui, LI Ze-xiao SEISMOLOGY AND GEOLOGY    2020, 42 (5): 1091-1108.   DOI: 10.3969/j.issn.0253-4967.2020.05.005 Abstract （410）   HTML    PDF（pc） （4980KB）（482）       Knowledge map    Save Based on the rupture model of Mainling M6.9 earthquake in Tibet on November 18, 2017, the spatial distribution of static Coulomb failure stress change at different depths are calculated respectively according to two different receiving fault selection schemes. The one scheme is that we set the parameters of receiving fault at different position to be consistent with the main shock; The other scheme is on the assumption that fault's orientation is randomly distributed under the ground, and we select the receiving fault which is most prone to slide under the influence of coseismic stress field produced by main shock. Therefore, the geometrical orientation of receiving fault will vary with space. According to the above two results of static Coulomb failure stress change, we discussed the static Coulomb stress influence produced by the main shock to short-term aftershocks and the Medog M6.3 earthquake in Tibet on April 24, 2019, respectively. The result shows that: 1)When the parameters of receiving fault are same with the main shock, the proportion of aftershocks in the positive zone of static Coulomb failure stress change is small at each depth. The focal mechanisms of aftershocks in the positive zone of static coulomb fracture stress are deemed similar to the main shock. We thought that they are motivated by the continuous rupture of the main shock. 2)Most of the aftershocks are in the negative zone of static Coulomb failure stress change at each depth. We inferred that this phenomenon which may be on account of the focal mechanisms of these aftershocks is quite different with the main shock. From the result of receiving fault to choose the most prone to slide under the coseismic stress field produced by main shock, we can clearly see that all the aftershocks are within the zone of static Coulomb failure stress change greater than the trigger threshold of 0.01MPa at different depths. It indicates that all the aftershocks are likely to be triggered. It was speculated that the aftershocks in the negative zone of static Coulomb failure stress change occurred in the crushed zone caused by violent rupture of the main shock. There are countless cracks in the crushed zone, and the orientation of these cracks is abundant. Perhaps, because most aftershocks occurred on these various cracks, their focal mechanisms are quite different from the main shock. The value of elastic constants will be reduced significantly in the crushed zone. All the results in this paper also indicate that considering the elastic constants difference between in and out of the source region is beneficial to accurately estimate the static Coulomb stress influence between earthquakes in the source region. 3)Different institutes and authors used different data and methods to get several different focal mechanisms of the Medog earthquake. According to these results, we calculated a central focal mechanism solution, which has a minimum difference with these focal mechanisms. On the basis of this central focal mechanism solution, the static Coulomb stress influence of the Mainling earthquake to the Medog earthquake is calculated quantitatively. Result indicates that the magnitude of static Coulomb failure stress change generated by the Mainling earthquake is quite small on both two nodal planes of the central focal mechanism solution of the Medog earthquake, this means that the Medog earthquake is independent of the Mainling earthquake. Reference | Related Articles | Metrics

Select

AN ANALYSIS ON MS 8.0 WENCHUAN EARTHQUAKE FAULT AND SEISMIC DISASTER ZHAO Bo-ming, XU Xi-wei SEISMOLOGY AND GEOLOGY    2008, 30 (4): 839-854.   Abstract （2992）      PDF（pc） （11489KB）（2666）       Knowledge map    Save Complex spatial distribution of seismic motion near faults has always been a concern to scientists,and it still remains as an uncertain problem due to insufficiency of events and information.The paper presents the main cases of seismic disaster by field investigations of MS 8.0 Wenchuan earthquake,analyzes and discusses the relationship among earthquake fault,ground motion and earthquake disaster near the fault fractured zone,based on previous research of source rupture processes and source inversion of Wenchuan earthquake.Intensive deformation and ground surface rupture along the earthquake fault have caused obvious damage to buildings,so it is necessary to introduce the safety distance away from active fault and other measures.Possible reasons for buildings near surface rupture zone having withstood the strong earthquake are as follows:other than their performance of seismic resistance,firstly,most of them locate at hard sites or on bedrock in the surface rupture zone,and secondly,the effective stress drop and low rupture velocity may exist in the shallow asperities,resulting in a relatively lower ground motion at the period about 1 sec. Related Articles | Metrics

Select

THE RETROGRESSIVE EROSION RATE AT HUKOU WATERFALL, YELLOW RIVER AND THE RELATION TO THE HANCHENG FAULT YAN Xiao-bing, LI Zi-hong, ZHAO Jin-quan, HU Gui-rang, GUO Jin SEISMOLOGY AND GEOLOGY    2016, 38 (4): 911-921.   DOI: 10.3969/j.issn.0253-4967.2016.04.009 Abstract （546）      PDF（pc） （5484KB）（667）       Knowledge map    Save On the basis of consulting historical records about the positions of Hukou waterfall at different times,we conduct a field geological survey along the Yellow River and ultimately determine the specific locations of the Hukou waterfall in the different periods.Based on this,the retrogressive erosion rates in different periods are calculated as about 1.66m/year during the Xia Dynasty to the Tang Dynasty period,about 1.01m/year in the Tang Dynasty to the Yuan Dynasty,about 0.97m/year in the Yuan Dynasty to the Ming Dynasty,about 1.28m/year in the Ming Dynasty to the Republican period,and 0.6m/year from the Republican period to the present.Considering the complex geological conditions along the Yellow River,the average retrogressive erosion rate of Hukou waterfall on the Yellow River is obtained to be 1.51m/year since the historical records (early Qin Dynasty to the present).Lithology surrounding the Hukou waterfall includes mainly the Triassic gray,gray-green thick-layered mid-grained feldspar sandstone and dark purple,yellow-green mudstone,this hardness and softness combination feature is the unique geological condition of the Yellow River.After abrasing the softer shale driven by water cyclotron at this position,water washes off the debris,causing the overlying feldspar sandstone suspended for a long period.Feldspar greywacke block collapses under accumulative water erosion in long years,and then retrogressive erosion occurs in Hukou waterfall.In the process of 1 ︰ 50 000 active fault mapping of Hancheng Fault,we excavated a trench at Shaojialing,and the trench profile shows that:in the early and middle period of late Pleistocene,there are obvious surface ruptures produced by the fault.Cumulative offset near the trench is more than 20 meters in height difference.Yellow River terraces survey at Yumenkou also confirms that a fault slip of about 20 meters occurred during the early and middle period of the late Pleistocene.Assuming the retrogressive erosion rate is constant,the author thinks the Hancheng Fault was activated at early and middle age of the Late Pleistocene,forming a 20~30m high scarp (knick point),and today's position of Hukou waterfall may be the position of this knick point after the retrogressive erosion of about 40 to 50ka. Reference | Related Articles | Metrics

Select

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 （230）   HTML （17）    PDF（pc） （11724KB）（92）       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

Select

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 （290）   HTML （13）    PDF（pc） （16789KB）（89）       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

Select

GRAVITY PERTURBATION AND CHARACTERISTICS OF TEM-PORAL AND SPATIAL CHANGES OF BACKGROUND NOISE BE-FORE EARTHQUAKE: THE EXAMPLE OF MADUO MS7.4 AND YANGBI MS6.4 EARTHQUAKES GOU Jia-ning, LIU Zi-wei, JIANG Ying, ZHANG Xiao-tong SEISMOLOGY AND GEOLOGY    2023, 45 (1): 252-268.   DOI: 10.3969/j.issn.0253-4967.2023.01.014 Abstract （27）   HTML （4）    PDF（pc） （7560KB）（19）       Knowledge map    Save The Yangbi MS6.4 and Maduo MS7.4 earthquake occurred successively on May 21~22, 2021 in Dali, Yunnan Province and Guoluo, Qinghai Province of China. The earthquakes caused deformation of boundaries with density difference and changed the density of rocks around fault due to volumetric strains, thus, disturbing the earth’s gravity field. The Earth’s time-varying gravity field contains rich information about distribution and migration of materials in the Earth system and provides very important constraints for the structural and kinematics characteristics, the interaction of various layers and coupling mechanisms of the solid Earth. Therefore, gravity observation means a lot for earthquake monitoring. The background noise is the continuous high-frequency oscillation on the observation instruments placed on the surface of the earth, such as seismometers and gravimeters, which is affected by many factors such as oceans, atmosphere, wind fields, earthquakes, human activities, etc. The background noise of the gravimeter may vary in different times and locations. However, temporal and spatial variation of background noise before and after an earthquake has not been studied yet. The existing research has observed gravitational disturbance signals before major earthquakes, but it is difficult to capture them directly from the original gravity data without pretreatment. Permutation entropy(PE)can characterize the randomness of the signal or detect signal mutation, and has been widely used in biomedicine, finance, mechanical vibration time series. In this study, we use PE to detect gravitational disturbance signal from raw data and study the background noise changes before and after the earthquake. In this paper, 1Hz sampling records from 15 continuous tidal gravimeters(including the types from PET/gPhone to OSG)of Continuous Gravity Network of China, with spanning from 1th Jan to 30th June, 2021, were obtained and analyzed. Firstly, A bandpass filter(0.1~0.18Hz)was employed to extract gravity disturbance, after removing firstly the earth tides and atmospheric effects with the DDW model and a barometric admittance(-0.3×10-8m·s-2/mbar). The short time Fourier transform was used to determine the time-frequency characteristics of non-tidal gravity signals. Then, we calculated the PE and background noise magnitude(SNM)in seismic frequency band(200~600s)of the records. The results show that: 1)All kinds of gravimeters can record high-precision solid earth tide, and respond well to high-frequency fluctuation signals caused by most earthquakes above magnitude 6 in the world. 2)There was a set of gravity disturbance signals recorded by most stations on May 15~18th, and there were two other sets of disturbance signals at coastal stations. The disturbance amplitude was ±(10~100)μGal, and there was no evidence to show that the smaller the epicenter distance, the larger the disturbance amplitude. The large disturbance amplitude of coastal stations and the other two groups of disturbances may be related to sea wave pulsation or local rainfall. 3)The PE value of the original gravity record basically oscillated near a high value, in which the spring gravimeter was close to 1, and the superconducting gravimeter was 0.7. From this point of view, we find that the signal-to-noise ratio of superconducting gravimeter is higher than spring gravimeter; Without any preprocessing procedure on original gravity records, PE could effectively explore the abrupt-change signal in the records. The continuous and significant drop of PE corresponded to perturbation signal before the earthquake, and the instantaneous downward pulse of PE agreed with the tremor signal caused by the seismic wave. 4)We find that the background noise had a clear upward trend occurring two months(early March)before the earthquake; The spatial distribution of SNM indicates that the background noise of the gravimeter located in the northern Qinghai-Tibet Plateau and the Bayan Har block has a significant increase before the earthquake. 5)We preliminarily speculate that the preseismic gravity disturbance is the low-frequency tremor generated by the slow slip of seismogenic fault, and the increase in background noise before the earthquake may be related to the increased activity of seismogenic tectonic block. Table and Figures | Reference | Related Articles | Metrics

Select

GEOMETRIC CHARACTERISTICS OF CO-SEISMIC SURFACE RUPTURES AND ACTIVE FAULTS HAO Hai-jian, HE Hong-lin, WEI Zhan-yu, SHI Feng SEISMOLOGY AND GEOLOGY    2017, 39 (6): 1267-1282.   DOI: 10.3969/j.issn.0253-4967.2017.06.012 Abstract （501）   HTML    PDF（pc） （3090KB）（521）       Knowledge map    Save Fault traces contain abundant information associated with the fracture process and mechanism, so an accurate and quantitative description of their geometric characteristics is of great significance to perceiving the generation and development of faults. We collected 52 co-seismic surface ruptures and 300 active fault traces from across the world to analyse their geometric characteristics by the method of power spectrum density. Our results show that (1)the average power spectrum density has a distinct three-segment charateristic in the frequency domain. In the low frequency domain it represents the geometric characteristics of the boundary of tectonic block. In the medium frequency domain, the power spectrum density reflects the processes of lateral growth and connection of secondary faults, and the turn point on the 100 meters scale represents the effective resampling length, below which the power spectrum density characteristics are meaningless. (2)In the middle and high frequency domains, the power spectrum density curves of co-seismic surface ruptures show that there are obvious differences in roughness among three fault types, i.e. reverse > normal > strike-slip, which indicates that the geometric characteristics of co-seismic surface ruptures are controlled by the fault types. (3)Compared with co-seismic surface ruptures, active fault traces have much lower power spectrum density, indicating the roughness of active fault traces becomes lower with increasing numbers of rupturing events and the lengths of active history, i.e., the fault roughness is inversly proportional to its maturity. Reference | Related Articles | Metrics

Select

NEW EVIDENCE OF THE PALEOEARTHQUAKE RUPTURE IN THE NORTH GAIZHOU-ANSHAN SEGMENT OF THE JINZHOU FAULT LI An, WAN Bo, WANG Xiao-xian, JI Hao-min, SUO Rui SEISMOLOGY AND GEOLOGY    2023, 45 (1): 111-126.   DOI: 10.3969/j.issn.0253-4967.2023.01.006 Abstract （33）   HTML （8）    PDF（pc） （10588KB）（18）       Knowledge map    Save The Haicheng MS7.3 earthquake is the first successfully predicted earthquake in China, which saved a large number of lives and avoided property losses. However, the investigation after the earthquake did not find a continuous surface rupture zone, and only some ground fissures and sandblasting were found in the epicenter area. The isoseismal line of this earthquake shows obvious conjugate characteristics. Which fault is the seismogenic structure of the Haicheng earthquake has always been controversial. According to the focal mechanism and distribution of ground fissures, some scholars suggested the seismic structure is the Haicheng River Fault with a strike of NWW. However, other scholars suggested the Jinzhou Fault has a larger scale and controls the geomorphic boundary. Jinzhou Fault is also a major seismic structure distributed in the west of Liaodong Peninsula, with a strike of NENNE and a length of 280km. The north Gaizhou-Anshan segment of the Jinzhou Fault is conjugated with the Haicheng River Fault. Both of them are likely to be the seismogenic structure of the Haicheng earthquake, or both ruptured in the Haicheng earthquake. Based on remote sensing image interpretations, four sites of the fault scarps, including the Yujiagou, Houwudao, Dongjiagou, and Tashan sites, were distinguished and verified in situ. And using micro geomorphology measurement and paleoseismic trench excavation in the Huluyu site of the north Gaizhou-Anshan segment of the Jinzhou Fault which is conjugated with the Haicheng River Fault, this paper obtains the following understandings: The Jinzhou Fault extends from the northeast of the Dashiqiao City to the south of the Anshan City. There are prominent NE-trending fault scarps, which were formed in the late Pleistocene and Holocene, on geomorphic surfaces of the basin mountain transition zone. Due to farming and building, fault scarps are not preserved well, and the distribution of the fault scarp is discontinuous. The height of fault scarps is mostly 1~2m, up to 3m at most. The paleoseismic trench was excavated in the Huluyu village, south of Haicheng City. The paleoseismic trench revealed a ~20m wide bedrock fracture zone in the north Gaizhou-Anshan City segment of the Jinzhou Fault. Three Late Pleistocene to Holocene strata(U3 to U5)overlie the bedrock fracture zone. Five fault planes(F1 to F5)are revealed in the trench. The fault F1 recorded the newest paleoearthquake event and the Fault F2 recorded the earlier one. In summary, according to the cover-cut relationship between strata and faults, at least two paleoseismic events occurred from the Late Pleistocene((37.6±2.2)ka)to the Holocene. The newer one occurred in the Holocene(after(11.7±0.8)ka, probably 400~500a before present). However, because of the thin Holocene strata, we cannot distinguish more paleoearthquakes in the trench. Therefore, it is still doubtful whether the north Ganzhou-Anshan segment of the Jinzhou Fault ruptured in the Haicheng earthquake in 1975. However, the confident conclusion is that the north Gaizhou-Anshan City segment of the Jinzhou Fault is an active fault in the latest Late Pleistocene to Holocene. Table and Figures | Reference | Related Articles | Metrics

Select

A REVIEW ON SITE CLASSIFICATION METHOD AND ITS APPLICABILITY IN EARTHQUAKE ENGINEERING PENG Yan-ju, LÜ Yue-jun, HUANG Ya-hong, SHI Chun-hua, TANG Rong-yu SEISMOLOGY AND GEOLOGY    2009, 31 (2): 349-362.   DOI: 10.3969/j.issn.0253-4967.2009.02.016 Abstract （2037）      PDF（pc） （434KB）（6153）       Knowledge map    Save Two kinds of site classification methods commonly used in earthquake engineering are analyzed in this paper.One is standard methods stipulated in seismic codes,and used to determine the site effects on seismic parameters for the seismic resistance of structures,the site classification methods and site indexes in seismic codes of China,United States,Europe and Japan are presented,and the problems about site index are discussed,such as the calculation method and depth of shear wave velocity,the choice of initial layer,the grade of overburden thickness,etc.Then some suggestions are put forward for the new generation of seismic code in China.The other kind of site classification methods is used to predict site effects on a large scale for a regional seismic hazard prediction.The popularly studied methods based on geology,topography and geomorphology are described in detail.The common character of this kind of methods is to find an easily obtained macro index,and to summarize the rules between the macro index and the site index in seismic codes(shear wave velocity in most cases),and then the regional site category zonation can be delineated.The response spectrum methods of ground motion are also presented here,such as RSS(Response Spectral Shape)and HVSR(Horizontal-Vertical Spectral Ratio),they can be used in areas with abundant ground motion records.Finally the advantage,limitation and applicable scope of these methods are discussed. Related Articles | Metrics

Select

AN EXPERIMENTAL STUDY ON THE TRANSIENT CREEP OF GRANITE NIU Lu, ZHOU Yong-sheng, YAO Wen-ming, MA Xi, HE Chang-rong SEISMOLOGY AND GEOLOGY    2021, 43 (1): 20-35.   DOI: 10.3969/j.issn.0253-4967.2021.01.003 Abstract （370）   HTML    PDF（pc） （5536KB）（197）       Knowledge map    Save Many of the large earthquakes in the continental crust nucleate at the bottom of the seismogenic zone in depths between 10 and 20km which is related to the broad so-called ‘brittle-to-plastic or brittle-to-ductile’ transition region. From the field studies and seismic data, we could know that the dominant deformation mechanism at the base of seismogenic zone is likely to be semi-brittle flow of fault rocks. The physical and chemical processes acting in the ‘brittle-to-plastic’ transition are of great interest for a better understanding of fault rheology, tectonic deformation of the continental lithosphere and the generation of strong earthquakes. So it’s of great significance to know more about this transition. Despite the importance of semi-brittle flow, only few experimental studies are relevant to semi-brittle flow in natural rocks. In order to study the semi-brittle deformation and rheological characteristics of granite, we performed a series of transient creep experiments on fine-grained granite collected from the representative rock of Pengguan Complex in Wenchuan earthquake fault area using a solid-medium triaxial deformation apparatus(a modified Griggs rig). The conditions of the experiments are under the temperatures of 190~490℃and the confining pressures of 250~750MPa with a strain rate of 5×10-4s-1. The temperature and pressure simulate the in-situ conditions of the Wenchuan earthquake fault zone at the corresponding depths of 10~30km. We observe the microstructures of the experimentally deformed samples under the scanning electron microscope(SEM). The mechanical data, microstructures and deformation mechanism analysis demonstrate that deformation of the samples with experimental conditions could be covered by three regimes: 1)Brittle fracture to semi-brittle flow regime. We could see the strain and stress curves of the samples characterizing with strain hardening behavior and without definite yield point under low temperatures and pressures, which correspond to the depths of 10~15km; 2)Brittle-ductile transition regime. The strain and stress curves of the samples tend to be in a steady state with definite yield point under temperature and pressure at the depths of 15~20km. The main deformation mechanism is cataclasis, and dynamic recrystallization and dislocation creep are activated; and 3)Ductile flow regime which is at depths of 20~30km. The strength of granite increases with depth and reaches to the ultimate at the depth of 15~20km, and then decreases with depth at 20~30km. Based on the analysis of strength of granite, microstructures and deformation mechanism, we conclude that the granitic samples deformed with the characteristics of transient creep, and the strength of Longmenshan fault zone reaches maximum at the depths of 15~20km where it is in the brittle-to-plastic regime. Based on the Mohr circle analysis, the rupture limit at depths of 15~20km is close to the limit of friction, and at the same time, this depth range is also consistent with the focal depth of Wenchuan earthquake. Therefore, it implicates that the deformation and strength of Pengguan complex granitic rocks should control the nucleation and generation of the Wenchuan earthquake. Reference | Related Articles | Metrics

Select

THE CHARACTERISTIC AND DEEP STRUCTURE OF THE GEOMAGNETICS IN AND AROUND THE DUNHUA-MISHAN FAULT ZONE WANG Yu-dan, ZHANG Jing-fa, TIAN Tian SEISMOLOGY AND GEOLOGY    2022, 44 (2): 448-460.   DOI: 10.3969/j.issn.0253-4967.2022.02.011 Abstract （227）   HTML （8）    PDF（pc） （6108KB）（66）       Knowledge map    Save This paper focuses on the in-depth analysis of the aeromagnetic characteristics of the Dunhua-Mishan fault zone and its surrounding areas using wavelet multi-scale analysis. In order to analyze the anomalies of the crustal structure at different depths, wavelet multi-scale decomposition is used to separate the deep field from the shallow field sources, superimpose the aeromagnetic anomalies on different anomalies of different geological bodies, extract the required information, analyze the local field anomalies caused by the field sources, and invert and interpret the geological bodies. In this paper, wavelet multi-scale analysis is used to decompose the aeromagnetic data, separate the deep and shallow field sources of aeromagnetism in the study area, and obtain wavelet detail maps of order 1 to 4. The wavelet transform detail maps are a response to high frequency anomaly information, and also a reflection of local field aeromagnetic anomaly information, which can be used to infer information such as fault depth and basement depth of basin. The experimental results are used to analyze the anomaly characteristics at different depths, invert and analyze the characteristics of the aeromagnetic anomalies and crustal structure at different depths, explore the deep basement and fault tectonic features and the intersection relationship between the Dunhua-Mishan Fault and the surrounding faults, calculate the approximate field source depth by wavelet detail map and power spectrum method, and infer the fault cut-through depth. The results of the analysis can provide geophysical research information for the study of geotectonics and the evaluation and exploration of hydrocarbon resources. Based on the original aeromagnetic anomaly map, aeromagnetic anomalies ranging from -494~2022nT can be obtained, with the highest anomaly located at about 50km from Baoqing County. The anomalies in the central part of the study area are high, while those in the eastern and western parts are low. The deposition of basal and ultramafic magmatic rocks in the Dunhua-Mishan area has caused massive high anomalies, while deep and large faults caused basement uplift or decline, shown as high and low anomaly zones. In the aeromagnetic shallow source field, the shallow surface and upper crustal media are more complex, and the Dunhua-Mishan fault zone shows multi-pearl-like small-scale anomalies, resulting mainly from the intrusion of basal or ultramafic magmatic rocks in the shallow part of the fault. In the deep source field, the magnetic anomalies in middle and lower crust are mainly caused by different magnetic properties of basin bedrock. The large fault zone presents as the dividing line of different trajectory feature zones, and the deep large fault cuts deeper and presents as the dividing line of different trajectory feature zones. The cut-through depth of the deep major faults is larger and affects the aeromagnetic characteristics of the deep tectonic zone. The paper further discusses the cut-through depth of the major faults of this region by analyzing the characteristics of the aeromagnetic anomalies at different depths and finds that there are the three deep major faults in the region, namely, the Dunhua-Mishan Fault, the Dahezhen Fault and the Yilan-Yitong Fault, while the Hulin River Fault, the Muling River Fault, the Fujin-Xiaojia River Fault and the Nanbeihe-Boli Fault only cut through the shallow crust; the Muling River Fault, the Dunhua-Mishan Fault, the Dahezhen Fault and the Fujin-Xiaojia River Fault only intersect in the shallow crust. The Parker method was used to invert the depth of the Curie points in the area, and the results show that the depth of the Curie points in the area ranges from 22.3~29.9km, with the deepest area in the south of Hulin County, which is a depressional basin formed by plate subduction and extrusion, and the Dunhua-Mishan fault zone has a controlling effect on the morphology of the Curie points. Seismic activity is low in the region as a whole, and earthquakes are densely distributed in the northwest of the study area along the Yilan-Yitong fault zone, and less distributed along the Dunhua-Mishan fault zone and the Dahezhen fault zone. In the vicinity of the Dunhua-Mishan fault zone, small earthquakes are mainly concentrated in the area south of the Mishan sub-uplift, and the northern section of the Dunhua-Mishan fault zone is generally more stable. The gravity field in this area has been studied in depth by previous authors. The area belongs to the Moho surface uplift zone in Heilongjiang Province, with the Moho depth of about 30~32.5km. The Yilan-Yitong rift zone is deep to the Moho surface, and the Moho surface often shows uplift in the seismically active area. The local deformation and uplift of the crust-mantle provides the possibility of stress concentration, while the existence of deep major faults provides a channel for material transport. The overall level of seismic activity in the region is low, and the areas with intense activity are mainly concentrated in the Yilan-Yitong fault zone, with small earthquakes also gathering near the Jixi area. Seismicity of Qitaihe-Jixi area is mainly influenced by the Mudanjiang Fault and the Nanbei River Fault. The Dunhua-Mishan Fault has a strong influence on the distribution of Curie points and also influences the formation of several major tectonic units. So, more attention should be paid to the crustal activity of areas around the faults and at the intersections of faults in the future. Table and Figures | Reference | Related Articles | Metrics

Select

SCHMIDT HAMMER EXPOSURE AGE DATING OF ANCIENT EARTHQUAKE-INDUCED BEDROCK LANDSLIDES AND ROCK AVALANCHES IN THE NORTHERN MARGIN OF QINLING MOUNTAINS SHI Wen-fang, XU Wei, YIN Jin-hui, ZHENG Yong-gang SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1384-1402.   DOI: 10.3969/j.issn.0253-4967.2022.06.003 Abstract （205）   HTML （11）    PDF（pc） （8627KB）（77）       Knowledge map    Save It is difficult to use traditional trenching and field geological investigation to yield the age of paleoseismic events along active fault in western mountainous areas of China where the geomorphic trace mark and sediments are often eroded or altered by human activities. The recurrence interval of paleoearthquake possesses greater uncertainty. It is necessary to yield ages of paleoearthquake event from different ways and examine the reliability of paleoearthquake results. In these regions, an earthquake with magnitude greater than 7 can produce rock avalanches around 200~400km away from the epicenter, such as the Wenchuan earthquake in 2008, due to their structure setting of strong neotectonic activity and the higher topographic relief. Therefore, the seismic bedrock landslide and rock avalanche can record the occurrence time, intensity and damage of strong earthquake in the mountainous area. This provides a new way to assess the frequency and intensity of paleoearthquake occurring in the intraplate continental areas(such as the north-south seismic zone)where strong earthquakes recurred for hundreds to thousands of years based on the seismic landslide records. Identifying ancient earthquake bedrock collapse relics in Quaternary deposits and accurately determining their ages will not only help broaden the study on the recurrence history of active fault, but also assess the earthquake risk in mountainous area. As shown by previous studies, the Schmidt-hammer exposure-age dating(SHD)method is a relatively simple, rapid, cheap and non-destructive in-situ exposure age dating method. In this study, ancient earthquake bedrock landslides and rock avalanches with known historical records distributed on the Qinling northern piedmont fault and the Huashan piedmont fault are used to preliminarily establish the rock weathering factor with age calibration curve. The rebound values of rock surface at dozens of sampling sites of each rock avalanche and landslide are measured by Schmidt hammer and analyzed statistically. The weathering factor of the exposed rock of each rock avalanche and landslide is calculated and the solution of SHD method is discussed. The reliability of SHD is evaluated according to the measured data and the records of historical age. The main conclusions are as follows: (1)The Schmidt hammer rebound value of rock surface at three ancient earthquake bedrock landslides and rock avalanches is negatively correlated with their historical ages. The older the historical record age, the lower the average rebound value of the rock, and vice versa. Based on the statistical analysis of weathering factors of rocks of bedrock landslides and rock avalanches, a preliminary age calibration curve is obtained as T=(19 723±888)×fw-(2 145±166). This curve can be used to infer the bedrock landslides and rock avalanches of more than 5×102 a BP, and it provides a new relative dating method for the ancient bedrock landslide and rock avalanches within the age of 3 000a BP in the northern margin of the Qinling Mountains. (2)Under the climatic and lithological conditions of the northern margin of the Qinling Mountains, the relative ages of bedrock landslide and rock avalanches can discriminate the interval of millennium scale according to the rock rebound value measured by Schmidt hammer. However, it cannot distinguish the difference in weathering degree of the bedrock landslide and rock avalanches with the interval of less than 500 years. (3)The Schmidt hammer rebound value measured repeatedly on fresh rocks shows that the fluctuation range of the rebound values is small, within the value of 0-3, which is helpful to rapidly select qualified sampling sites for terrestrial in-situ cosmogenic nuclide dating(TCND). Thus, the Schmidt hammer value can be used to evaluate whether the rock samples have the problem of nuclide inheritance induced by complex exposure history such as post-exposure and secondary transportation. This would introduce greater objectivity to the sample selection and possibly require less samples, thus reducing the costs; meanwhile, it will improve the dating efficiency and ensure the reliability of TCND. Therefore, SHD method is a valuable complementary method to TCND. (4)Under the climatic and lithological conditions in the northern margin of the Qinling Mountains, the rebound value decreases by (25%±1%) for rocks after weathering for 2ka, by (16%±1%) for 1ka, and by (15%±1%) for 0.5ka. Table and Figures | Reference | Related Articles | Metrics

Select

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 （183）   HTML （9）    PDF（pc） （28982KB）（93）       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

Select

STRUCTURAL DEFORMATION CHARACTERISTICS OF BO-A FAULT IN THE SOUTHWESTERN MARGIN OF TURPAN BASIN MA Jian, WU Guo-dong, LI Jun, HUANG Shuai-tang SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1469-1483.   DOI: 10.3969/j.issn.0253-4967.2022.06.007 Abstract （132）   HTML （19）    PDF（pc） （11013KB）（63）       Knowledge map    Save The Bolokenu-Aqikekuduke Fault(Bo-A Fault)is a large-scale right-lateral strike-slip fault zone, which starts in Kazakhstan in the west, enters China along the NW direction, passes eastward through Alashankou, Lake Aibi and the southwestern margin of Turpan Basin, and terminates in the Jueluotage Mountain, with a total length of about 1 000km. At present, researches on the fault mainly focus on the area from Lake Alakol to Jinghe. Through satellite images, it can be found that the Bo-A Fault enters the southwestern margin of the Turpan Basin in the SE direction, and offset various landforms such as river terraces and alluvial fans, forming clear linear features on the surface, which indicates that there have been obvious activities since late Quaternary in this fault section. However, no detailed research has been carried out on the tectonic deformation characteristics of the Bo-A Fault in this area. The active characteristics of the faults in the southwestern margin of the Turpan Basin are studied, and the results are helpful to understand the role of the Bo-A Fault in the Cenozoic tectonic deformation of the Tianshan Mountains. The study area is located in the southwestern margin of the Turpan Basin, where three stages of alluvial-proluvial fans are developed. The first-stage alluvial-proluvial fan is called Fan3, which was formed earlier and its distribution is relatively limited, formed roughly in the early late Pleistocene; The second-stage alluvial-proluvial fan is called Fan2, which is the most widely distributed geomorphological surface in the study area. The geomorphic surface in this period was roughly formed from the late Pleistocene to the early Holocene. The third-stage alluvial-proluvial fan is called Fan1, which belongs to the Holocene accumulation, most of which are located at the outlet of gullies near the mountain passes, forming irregular fan-shaped inclined surfaces. To the west of Zulumutaigou, the fault offset the Fan3 alluvial-proluvial fan, forming dextral dislocation and fault scarp of the gully on the surface. The measurement shows that the amount of the dextral dislocation produced by the fault is between 22m and 40m. The height of the scarp is 3.9~4.2m. The section exposed by the fault shows that the Paleozoic bedrock thrust northward onto the Quaternary gravel layer, and the fault fracture width is about 1m, which reflects that the Bo-A Fault also has a certain thrust component. On the east bank of Zulu Mutaigou, the fault offset the Fan3 alluvial-proluvial fan, and the measurement results show that the offset of the gully is between 46.3m and 70.2m. To sum up, the movement mode of the Bo-A Fault in the study area is dominated by dextral strike-slip. On the Fan2 alluvial-proluvial fan at the northwest of Zulu Mutaigou, there are two secondary faults arranged in a right-step en-echelon pattern, forming high scarps with a height of 1.6~3.9m on the surface. Trench profiles reveal that both faults are SW-dipping thrust faults, thrusting from south to north, and they are preliminarily judged to be formed by the expansion of the Bo-A Fault into the basin. There are mainly three stages of alluvial-proluvial fans developed in the study area. Although no specific dating results have been obtained in this work, we believe that the age of the Quaternary landforms in the study area is the same as that in the Chaiwopu Basin, which is only separated by a mountain. Quaternary geomorphological ages are basically the same. Through geomorphological comparison, we believe that the age of Fan2 alluvial-proluvial fan is 12~15ka, and the age of Fan3 alluvial-proluvial fan is 74ka. It is estimated that the dextral slip rate of the Bo-A Fault is about 1mm/a since the formation of Fan3, and the vertical movement rate of the fault is about 0.13~0.32mm/a since the formation of Fan2. According to GPS observations and geological data, the NS-direction shortening rate in the East Tianshan area can reach 2~5mm/a. Through this study, it can be found that the Bo-A Fault also plays a role in regulating the near-NS-trending compressive stress in the East Tianshan area by accommodating the compression strain inside the Tianshan Mountains mainly through the NWW-directed right-lateral strike-slip motion. In addition, in the study area, the youngest fault scarp is located on the Fan2 alluvial-proluvial fan at the north of the main fault. It is preliminarily judged that the latest activity of the Bo-A Fault has a tendency to migrate from the mountain front to the basin. Table and Figures | Reference | Related Articles | Metrics

Select

GEOCHEMICAL CHARACTERISTICS OF SOIL GAS IN THE FAULT ZONES OF NORTH TIANSHAN, XINJIANG JIANG Yu-han, GAO Xiao-qi, YANG Peng-tao, LIU Dong-ying, SUN Xiao-long, XIANG Yang, ZHU Cheng-ying, WANG Cheng-guo SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1597-1614.   DOI: 10.3969/j.issn.0253-4967.2022.06.014 Abstract （107）   HTML （13）    PDF（pc） （6678KB）（58）       Knowledge map    Save The soil gas concentration and escape rate value can sensitively and objectively reflect the underground state of stress, strain and tectonic activity. In addition, abnormal phenomena of fault soil gas often occur before and after seismic activity. It is often used to identify the active state of fault zones, explore hidden faults and assess earthquake risk. As an important geochemical method, the soil gas measurement is an important geochemical method to reveal fault properties and fault activities and other tectonic activities. In this study, we laid out 8 measurement lines of soil gas along the Borokonu-Aqikkuduk Fault, the Kusongmuchike piedomont fault, the Dushanzi-Anjihai Fault, the Horgos-Tugulu Fault, the Kashi River Fault and the Nalati Fault in two earthquake risk areas of the north Tianshan Mountains in Xinjiang, namely, the “North Tianshan Wenquan-Jinghe M7 earthquake risk area” and the “Wusu-Hejing M6 earthquake risk area”. From 2017 to 2020, a total of 6~7 phases of measurements were carried out to make clear the distribution characteristics of Rn, CO2 and Hg concentrations along these faults. There have been many moderate/strong earthquakes near the above-mentioned faults, and it is of great significance of soil gas measurement on these faults for us to gain a deep understanding of the fault activity characteristics and earthquake risk. In this paper, the spatial distribution characteristics of fault soil gas are analyzed based on the multi-period measurement results, and the activity of the fault zone and the regional earthquake risk are discussed respectively. The results show that: 1)The Rn concentrations are more stable than that of CO2 and Hg along each measurement line, which can be used as an effective indicator gas for analyzing the distribution of fault zones, indicating the location of fault fractures and judging the activity of faults. Since there are many interference factors of CO2 and Hg concentrations, they can be used as an auxiliary means. In most cases, the distribution of Rn concentrations on other measuring lines is of single-peak shape, indicating that the soil gas concentration is higher at the outcrops of the fault. However, the concentrations of Rn in the Kusongmuchike piedmont fault and the Horgos-Tugulu Fault are higher, and the distribution curve of Rn concentrations shows multiple high-value forms, indicating that there are other fractures and broken positions on the fault zone besides the fault exposure position. 2)The highest Rn concentrations on the measuring lines of the Kusongmuchike piedmont fault, the Nalati Fault and the Horgos-Tugulu Fault are 99 802Bq/m3, 80 549Bq/m3, 78 834Bq/m3, which are not only higher than the Rn concentration of other measurement lines in the same period, but also higher than the highest Rn concentration of 58 205Bq/m3 in the Hutubi North Fault. The fault activity is relatively stronger. 3)The earthquake risk of Wenquan-Jinghe area is relatively low, with relatively high regional stress accumulation. In addition, the fault activity in this area is intensive, and moderate to strong earthquakes are more likely to occur, so there is a certain earthquake risk. In a word, it is of great scientific significance to carry out the activity detection and seismic risk assessment of the main active faults in the northern Tianshan area of Xinjiang. In the future, monitoring and in-depth research on the geochemistry of fault soil gas in the “North Tianshan Wenquan-Jinghe earthquake risk zone” is of great significance for judging the earthquake risk in the north Tianshan area. The results of this paper provide geochemical data for analyzing the characteristics of gas released by the fault zone in the northern Tianshan area of Xinjiang, and for guiding the selection and layout of seismic stations, as well as for seismic situation tracking and anomaly ascertainment. Table and Figures | Reference | Related Articles | Metrics

Select

PRELIMINARY INVESTIGATION ON DEFORMATION CHARACTERISTICS AND ACTIVITY OF LONGQUANSHAN FAULT BELT IN SICHUAN WANG Wei-tao, JIA Dong, LI Chuan-you, ZHENG Wen-jun, WEI Zhan-yu SEISMOLOGY AND GEOLOGY    2008, 30 (4): 968-979.   Abstract （2460）      PDF（pc） （9346KB）（3207）       Knowledge map    Save Based on the field work and seismic reflection profiling data,the paper investigates the deformation characteristics of the Longquanshan Fault zone.The main thrust fault of the Longquanshan Fault belt lies in the west of the Longquanshan anticline and has different properties from northeast to southwest.In the north segment and south segment of the Longquanshan Fault,the plane of fault dips to northwest and is uncontinuous,but in the middle segment,the plane of fault dips to southeast and is continuous.Therefore,the middle part of the fault is the main segment of the Longquanshan Fault.Structural geometries of the middle segment of the fault suggest classical fault-propagation folding and the fault ruptured along different axial directions.Historical earthquakes and geomorphological response to activity of the Longquanshan Fault indicate that the fault was active from the early Pleistocene to late Pleistocene,and its activity is weak since the late Pleistocene,and gradually decreases from south to north. Related Articles | Metrics

Select

RE-EVALUATION OF SEISMOGENIC AND OCCURRENCE CONDITIONS OF LARGE EARTHQUAKES ON STRIKE-SLIP FAULTS DENG Qi-dong, ZHU Ai-lan, GAO Xiang SEISMOLOGY AND GEOLOGY    2014, 36 (3): 562-573.   DOI: 10.3969/j.issn.0253-4967.2014.03.002 Abstract （624）      PDF（pc） （5689KB）（10533）       Knowledge map    Save Strike-slip fault are the active faults that are most closely related to large earthquakes. The study on how a large earthquake develops and occurs on strike-slip faults is an issue much concerned with the seismologists. As it is shown by structural geology studies, strike-slip faults are a complex tectonic system, which represents combination of various types of deformation under the shearing forces. Based on the research cases of various strike-slip fault zones both at home and abroad, this paper investigates and summarizes the geometry, kinematics and evolution processes of continuous or discontinuous strike-slip faults and analyzes the hinge role of the strike-slip faults. It is found that the hinge axis area is subject to intense compression, and the area is locked, where stress is concentrated, strain is localized, and earthquakes nucleate and develop. When the locked hinge axis is broken through, unstable sliding will occur along the strike-slip fault, producing sudden big displacement, accompanied with large earthquake. In the stepover zones of discontinuous strike-slip faults, earthquakes of corresponding size and type will develop and occur according to the relevant stress fields and rupture mechanics. Reference | Related Articles | Metrics

Select

TEMPORAL ORDERLINESS OF EARTHQUAKES (M≥8) ON CHINA MAINLAND——A NEW APPROACH TO THE PREDICTION OF EARTHQUAKES Xu Dao-yi, Huang Jian-fa, Wang Xiang-nan SEISMOLOGY AND GEOLOGY    1991, 13 (3): 231-240.   Abstract （1305）      PDF（pc） （1156KB）（1162）       Knowledge map    Save Some great earthquakes of magnitude 8 or greater on China mainland repeatedly occurred at the intervals of 252, 94, 48, and 25 years. It incited us to study the time interval between every pair of great earthquakes (M≥8) on China mainland. The result shows that there are four groups of clear orderliness distinguished in the most disorder distribution of earthquakes. The distinguished orderliness can be used to estimate the occurrence of next great earthquakes in China. Related Articles | Metrics

Select

A STUDY REVIEW ON CHARACTERISTICS OF SEISMIC ACTIVITY OF ACTIVE-TECTONIC BLOCK BOUNDARIES IN MAINLAND CHINA SHAO Zhi-gang, FENG Wei, WANG Peng, YIN Xiao-fei SEISMOLOGY AND GEOLOGY    2020, 42 (2): 271-282.   DOI: 10.3969/j.issn.0253-4967.2020.02.002 Abstract （446）   HTML    PDF（pc） （2034KB）（546）       Knowledge map    Save More than 80 percent of strong earthquakes(M≥7.0)occur in active-tectonic block boundaries in mainland China, and 95 percent of strong earthquake disasters also occur in these boundaries. In recent years, all strong earthquakes(M≥7.0)happened in active-tectonic block boundaries. For instance, 8 strong earthquakes(M≥7.0)occurred on the eastern, western, southern and northern boundaries of the Bayan Har block since 1997. In order to carry out the earthquake prediction research better, especially for the long-term earthquake prediction, the active-tectonic block boundaries have gradually become the key research objects of seismo-geology, geophysics, geodesy and other disciplines. This paper reviews the research results related to seismic activities in mainland China, as well as the main existing recognitions and problems as follows: 1)Most studies on seismic activities in active-tectonic block boundaries still remain at the statistical analysis level at present. However, the analysis of their working foundations or actual working conditions can help investigate deeply the seismic activities in the active-tectonic block boundaries; 2)Seismic strain release rates are determined by tectonic movement rates in active-tectonic block boundaries. Analysis of relations between seismic strain release rates and tectonic movement rates in mainland China shows that the tectonic movement rates in active-tectonic block boundaries of the eastern region are relatively slow, and the seismic strain release rates are with the smaller values too; the tectonic movement rates in active-tectonic block boundaries of the western region reveal higher values, and their seismic strain rates are larger than that of the eastern region. Earthquake recurrence periods of all 26 active-tectonic block boundaries are presented, and the reciprocals of recurrence periods represent high and low frequency of seismic activities. The research results point out that the tectonic movement rates and the reciprocals of recurrence periods for most faults in active-tectonic block boundaries exhibit linear relations. But due to the complexities of fault systems in active tectonic block boundaries, several faults obviously deviate from the linear relationship, and the relations between average earthquake recurrence periods and tectonic movement rates show larger uncertainties. The major reason is attributed to the differences existing in the results of the current earthquake recurrence studies. Furthermore, faults in active-tectonic boundaries exhibit complexities in many aspects, including different movement rates among various segments of the same fault and a certain active-tectonic block boundary contains some parallel faults with the same earthquake magnitude level. Consequently, complexities of these fault systems need to be further explored; 3)seismic activity processes in active-tectonic block boundaries present obvious regional characteristics. Active-tectonic block boundaries of the eastern mainland China except the western edge of Ordos block possess clustering features which indicate that due to the relatively low rate of crustal deformation in these areas, a long-time span is needed for fault stress-strain accumulation to show earthquake cluster activities. In addition, active-tectonic block boundaries in specific areas with low fault stress-strain accumulation rates also show seismic clustering properties, such as the clustering characteristics of strong seismic activities in Longmenshan fault zone, where a series of strong earthquakes have occurred successively, including the 2008 M8.0 Wenchuan, the 2013 M7.0 Lushan and the 2017 M7.0 Jiuzhaigou earthquakes. The north central regions of Qinghai-Tibet Plateau, regarded as the second-grade active-tectonic block boundaries, are the concentration areas of large-scale strike-slip faults in mainland China, and most of seismicity sequences show quasi-period features. Besides, most regions around the first-grade active-tectonic block boundary of Qinghai-Tibet Plateau display Poisson seismic processes. On one hand, it is still necessary to investigate the physical mechanisms and dynamics of regional structures, on the other hand, most of the active-tectonic block boundaries can be considered as fault systems. However, seismic activities involved in fault systems have the characteristic of in situ recurrence of strong earthquakes in main fault segments, the possibilities of cascading rupturing for adjacent fault segments, and space-time evolution characteristics of strong earthquakes in fault systems. 4)The dynamic environment of strong earthquakes in mainland China is characterized by “layering vertically and blocking horizontally”. With the progresses in the studies of geophysics, geochemistry, geodesy, seismology and geology, the physical models of different time/space scales have guiding significance for the interpretations of preparation and occurrence of continental strong earthquakes under the active-tectonic block frame. However, since the movement and deformation of the active-tectonic blocks contain not only the rigid motion and the horizontal differences of physical properties of crust-mantle medium are universal, there is still need for improving the understanding of the dynamic processes of continental strong earthquakes. So it is necessary to conduct in-depth studies on the physical mechanism of strong earthquake preparation process under the framework of active-tectonic block theory and establish various foundation models which are similar to seismic source physical models in California of the United States, and then provide technological scientific support for earthquake prevention and disaster mitigation. Through all kinds of studies of the physical mechanisms for space-time evolution of continental strong earthquakes, it can not only promote the transition of the study of seismic activities from statistics to physics, but also persistently push the development of active-tectonic block theory. Reference | Related Articles | Metrics

Select

RESEARCH ON SHALLOW STRUCTURAL CHARACTERISTICS IN THE BANQUAN SEGMENT OF ANQIU-JUXIAN FAULT ZONE BASED ON SHALLOW SEISMIC REFLECTION PROFILING QIN Jing-jing, LIU Bao-jin, WANG Zhi-cai, FENG Shao-ying, DENG Xiao-juan, HUA Xin-sheng, LI Qian SEISMOLOGY AND GEOLOGY    2022, 44 (2): 349-362.   DOI: 10.3969/j.issn.0253-4967.2022.02.005 Abstract （344）   HTML （19）    PDF（pc） （3676KB）（143）       Knowledge map    Save The Anqiu-Juxian Fault is the latest active fault in Tanlu fault zone, which is also the seismogenic fault of Tancheng M8.5 earthquake in 1668. In order to probe the shallow structure and the characteristics of faults in the eastern graben of Tanlu fault zone, we applied the high-resolution shallow seismic reflection method with multifold overlaying and stacking. In addition, we laid out two shallow seismic reflection lines across the Anqiu-Juxian Fault and the eastern graben of Tanlu fault zone. The shallow seismic profiles clearly reveal the stratigraphic interface morphology and shallow fault characteristics. The results show that the eastern graben of Tanlu fault zone is a graben basin consisting of multiple faults, and the thickness of Quaternary strata and graben structure characteristics are obviously affected and controlled by Changyi-Dadian Fault F1 and Baifenzi-Fulaishan Fault F2. Also, the eastern and western sides of the graben are the basement uplift areas, and the sediment thickness of the Quaternary strata in uplift areas is less than 30m. There are thick Cenozoic strata deposited in the barben, the stratigraphic morphology changes greatly laterally, showing an inclined form which is shallow in the west and deep in the east, and the Cenozoic strata are in angular unconformity contact with the overlying strata. The deepest part of Quaternary strata in the graben is located near the horizontal distance of 7400m, and its depth is about 190m. The Anqiu-Juxian Fault revealed by the shallow seismic reflection profile is composed of two branch faults dipping in opposite direction, which merge into one fault in the deep section. According to the discernible buried depth of the upper breakpoints of these faults and the characteristics of the Quaternary activity, the activity of Baifenzi-Fulaishan Fault on the western boundary of the eastern graben of Tanlu fault zone is relatively weak and the discernible depth of the upper breakpoint is 53m, we infer that the Baifenzi-Fulaishan Fault is a pre-Quaternary fault. The Changyi-Dadian Fault on the eastern boundary of the eastern graben of Tanlu fault zone not only cut the bedrock’s top interface, but also revealed signs of dislocation since Quaternary. The discernible depth of the upper breakpoint of Changyi-Dadian Fault is about 26~33m. The Anqiu-Juxian Fault is the latest active fault in the study area, which possess the characteristics of large scale and large penetration depth. The fault controls the deposition of the Cenozoic strata in the graben and plays an important role in the formation of the the eastern graben of Tanlu fault zone. The discernible depth of the upper breakpoint of Anqiu-Juxian Fault is about 17~22m. Therefore, we infer that the active ages of Changyi-Dadian Fault and Anqiu-Juxian Fault are the late Pleistocene and Holocene, respectively. The research results can provide seismological evidence for further understanding of activity mode and activity age of the seismogenic fault of the 1668 Tancheng M$8\frac{1}{2}$ earthquake, as well as the near-surface characteristics and activity of the Banquan segment of the Tanlu fault zone. Table and Figures | Reference | Related Articles | Metrics

Select

COMPARATIVE STUDY ON THERMAL ANOMALIES DETECTION METHOD BEFORE STRONG EARTHQUAKE: TAKING THE 2014 MW6.9 YUTIAN EARTHQUAKE AS AN EXAMPLE WU Wei-ying, SHAN Xin-jian, QU Chun-yan, LI Xin-yan SEISMOLOGY AND GEOLOGY    2022, 44 (6): 1503-1520.   DOI: 10.3969/j.issn.0253-4967.2022.06.009 Abstract （142）   HTML （2）    PDF（pc） （9872KB）（38）       Knowledge map    Save The reliability of anomaly extracting methods is crucial for pre-seismic thermal anomalies research. However, there is a lack of relevant researches. We compared two commonly used anomaly extracting methods, Z-score(ZS)and Robust satellite technology(RST)method, taking the 2014 Yutian earthquake as a typical example and the 2008 Wenchuan earthquake as a validation. The four aspects of extracted results are compared qualitatively and quantitatively, including the extraction effect, sensitivity to slight change, suppression of background information and indication of seismic information in the actual earthquake case. Moreover, the extracted results of validation case are used to validate the reliability of typical case results. Many intermittent anomalies in surface temperature and outgoing longwave radiation appeared before Yutian earthquake. The frequency of anomalies increases with the proximity of earthquake. The spatial distribution of surface temperature and outgoing longwave radiation anomalies gradually concentrated around the fault zone at the same time. The largest surface temperature and outgoing longwave radiation anomalies occurred one month before Yutian earthquake. The difference between the extraction results of ZS and RST method is mainly manifested in the frequency and amplitude of anomaly changes. The frequency and amplitude of anomaly changes obtained by RST method are higher than those obtained by ZS method. To further explore the reason for these differences, we further evaluate the two methods quantitatively by combining the data of two non-seismic years before and after Yutian earthquake respectively. The sensitivity of anomaly extraction method represents its ability to identify the slight changes of thermal parameters caused by the seismogenic process. The two methods are sensitive to slight changes, but the RST method is better than ZS method. The background information represents normal variation in surface temperature and outgoing longwave radiation caused by non-seismic factors. Suppression of background information determines the accuracy of extraction results. The comparison results show that both methods have certain suppression effect to background information, but the ZS method is better. The spatial distribution of pre-seismic thermal anomalies is an important index for predicting earthquake information(e.g. time of occurrence and location of epicenter). The results of quantitative comparison through normalized distance index show that for surface temperature data, ZS method is slightly better than RST method in indicating the location of epicenter. However, RST method is better for outgoing longwave radiation data. The maximum value of normalized distance index of ZS method occurred closer to the origin time of earthquake. We used the same quantitative evaluation method for the validation earthquake case. The verification results show that in addition to the sensitivity to anomaly changes, the comparison results of the two earthquake examples are similar in terms of the ability to suppress background information and indicate earthquake information. The difference is that ZS method has a better ability to suppress background information and RST method is better in indicating earthquake epicenter in the verification earthquake example. The main reason for the difference in extraction effect between the two methods is that the RST method averages the ground feature classification, and the difference between the observed value and the average value of the classification makes the RST method have a certain amplification effect on the weak signal. The difference between the typical earthquake case and the verification earthquake case is mainly due to the different complexity of the object types in the regions. Based on the above research results, we believe that ZS method and RST method have certain ability to extract pre-seismic anomalies. However, comparatively speaking, the RST method also has a good effect on the extraction of anomalies caused by other factors, and there is uncertainty in the ground feature classification. We believe that ZS method is a more appropriate and simple anomaly extraction method in the general seismic anomaly change extraction. Table and Figures | Reference | Related Articles | Metrics

Select

THE MS8.0 WENCHUAN EARTHQUAKE SURFACE RUPTURES AND ITS SEISMOGENIC STRUCTURE XU Xi-wei, WEN Xue-ze, YE Jian-qing, MA Bao-qi, CHEN Jie, ZHOU Rong-jun, HE Hong-lin, TIAN Qin-jian, HE Yu-lin, WANG Zhi-cai, SUN Zhao-min, FENG Xi-jie, YU Gui-hua, CHEN Li-chun, CHEN Gui-hua, YU Shen-e, RAN Yong-kang, LI Xi-guang, LI Chen-xia, AN Yan-fen SEISMOLOGY AND GEOLOGY    2008, 30 (3): 597-629.   Abstract （3808）      PDF（pc） （49676KB）（3295）       Knowledge map    Save Field investigations show that the MS8.0 Wenchuan earthquake of 12th May 2008 ruptured two NW-dipping imbricate reverse faults along the Longmenshan Fault zone at the eastern margin of the Tibetan Plateau.This earthquake generated a 240km long surface rupture along the Beichuan-Yingxiu Fault characterized by right-lateral oblique faulting and a 90km long surface rupture along the Guanxian-Jiangyou Fault characterized by dip-slip reverse faulting.Maximum vertical and horizontal dispacements of 6.2m and 4.9m,respectively,were observed along the Beichuan-Yingxiu Fault,whereas a maximum vertical displacement of 3.5m occurred along the Guanxian-jiangyou Fault.This co-seismic surface rupture pattern,involving multiple structures,is among the most complicated of recent great earthquakes.Its surface rupture length is the longest among the co-seismic surface rupture zones for reverse faulting events ever reported.Aftershocks recorded by local network clearly outline the hanging wall of the Beichuan-Yingxiu Fault and indicate that the fault dips about 47? to the west.Industry seismic lines,in addition to surface ruptures and aftershocks,allow us to build a 3D model for the rupture geometry that shows crustal shortening is the dominant process along the Longmen Shan to accommodate long-term deformation.Oblique thrusting accomplished by the earthquake indicates that the east-southeastward extrusion of Tibet Plateau accommodates,in part,the continuing penetration of the Indian plate into the Eurasian plate,and this extrusion is transformed at the eastern margin of the Tibetan Plateau into crustal thickening and shortening along the Longmenshan Fault zone that is responsible for the growth of high topography in the region. Related Articles | Metrics

Select

CHARACTERISTICS OF TECTONIC STRESS FIELD AROUND THE YANGBI MS6.4 EARTHQUAKE AND ITS SURROUNDING AREAS ON MAY 21, 2021 AND ITS GEODYNAMIC IMPLICATION FAN Wen-jie SEISMOLOGY AND GEOLOGY    2023, 45 (1): 208-230.   DOI: 10.3969/j.issn.0253-4967.2023.01.012 Abstract （47）   HTML （2）    PDF（pc） （10373KB）（14）       Knowledge map    Save According to the determination of China Seismological Network, at 21:48:34 Beijing time on May 21, 2021, an MS6.4 earthquake occurred in Yangbi County, Dali Bai Autonomous Prefecture, Yunnan Province. The epicenter(25.67°N, 99.87°E)is located on the southwest boundary of the Sichuan-Yunnan rhombic block, with a focal depth of 8km. On the basis of the survey results of the Yunnan Eartquake Agency, the highest intensity in the earthquake area is VIII degree, and the long axis of the isoseismic line is NW-striking. We calculated the focal mechanism solutions of 11 MS≥4.0 events of May 21, 2021, Yangbi earthquake by the CAP method. Combined with the collected focal mechanism solutions of the surrounding historical earthquakes, we inverted the tectonic stress field around the epicenter and its adjacent areas and simulated the relative stress value and the distribution of the focal mechanism solution in the Yangbi area. We analysis and studies the characteristics of tectonic stress field variation in the study area and its relationship with earthquakes, dynamic significance and seismogenic mechanism. The results show that: 1)The Yangbi earthquake sequence and the focal mechanism solutions of historical earthquakes near the epicenter are mostly of strike-slip type, followed by the normal-fault type. 2)The Yangbi earthquake sequence is mainly distributed in the depth range of 4~8km. The depth of earthquakes in the study area is mostly above 15km underground, and they mainly occur in the brittle upper crust. The tectonic stress field is strike-slip type in the Yangbi source area, and the maximum principal stress is the NNW-SSE direction, which is basically consistent with the known regional tectonic stress field. The regional inversion results show that the maximum principal stress axis(σ1 axis)of the Sichuan-Yunnan rhombic block in the northeastern part of the study area is the NNW-SSE direction, and the minimum principal stress axis(σ3 axis)is the NEE-SWW direction. In the Lanping-Simao block, the σ1 axis becomes nearly NS, and the σ3 axis is close to EW. For the Tengchong and Baoshan blocks in the southwest part, the σ1 axis rotates in the NNE-SSW direction, and the σ3 axis is in the NWW-SEE direction. Judging from the uncertainty range under the 95%confidence level of the maximum principal stress azimuth, the variation range of the inversion results of most grid points in the study area is within 20°, indicating that the inversion results are relatively stable. In general, the orientation of the maximum principal stress axis and the minimum principal stress axis show a clockwise rotation trend from northeast to southwest. And the maximum principal stress axis direction distribution is similar to the GPS horizontal velocity field and other stress data results. The stress orientation inside the Sichuan-Yunnan block, Tengchong and Baoshan blocks is relatively consistent. But the stress changes in the block boundary zone, showing a certain difference, which may be caused by the difference in the dynamic action, movement mode and speed of the block. The regional tectonic stress field is affected by the interaction between different blocks. 3)The R-value increases gradually from northwest to southeast in the study area. And the increase in the R-value shows that the intermediate principal stress is mostly characterized by tensile stress, indicating that the compressive stress required for material migration decreases relatively. Combined with the geological tectonic background of the study area, it is considered that the movement speed of the block(material)gradually slows down, which is consistent with the surface deformation observations. According to the simulation results of the relative shear stress and relative normal stress of the Yangbi earthquake, the NW-oriented nodal plane of the Yangbi earthquake is the seismogenic fault plane of the earthquake. Combined with the seismic relocation and tectonic stress field inversion results, We analyzed the seismic mechanism of the Yangbi earthquake as follows: Under the NNW-nearly NS-trending tectonic stress, the NW-trending subvertical faults intersect with the regional principal compressive stress at a small angle, resulting in right-slip shearing along the optimal release nodal plane, and finally rupture leads to the occurrence of earthquakes. The Yangbi earthquake is located in the southwestern boundary zone of the Sichuan-Yunnan rhombic block. In recent years, the 2013 Eryuan MS5.5 and MS5.0 earthquakes and the 2017 Yangbi MS5.1 earthquakes were occurred along this boundary zone. The seismic activities here are very significant. The occurrence of moderate to strong earthquakes near the Sichuan-Yunnan rhombic block may indicate that the main active faults at the block boundary have accumulated a high level of elastic strain energy. In addition, the Yangbi earthquake manifested as a right-lateral strike-slip seismic activity on the NW-trending fault plane, and it is located southwest of the Sichuan-Yunnan rhombic block. It just shows that the Sichuan-Yunnan rhombic blockhas a SE-direction translational motion, which is consistent with the kinematic model of the Qinghai-Tibetan plateau material escaping eastward in the form of a rigid block, accompanied by a certain clockwise rotation, which is consistent with the long-term tectonic movement direction of the block. The Yangbi earthquake occurred under the dynamic background that the Sichuan-Yunnan rhombic block is continuously squeezed by the Qinghai-Tibetan plateau material. These research results have reference significance for understanding the seismic background and dynamic mechanism of the Yangbi earthquake. Table and Figures | Reference | Related Articles | Metrics

Select

THE SEISMOGENIC TECTONICS OF THE MS 6.8 BACHU-JIASHI,XINJIANG EARTHQUAKE IN FEB.24, 2003 SHEN Jun, CHEN Jian-bo, WANG Cui, WU Chuan-yong, SONG Zheng-na SEISMOLOGY AND GEOLOGY    2006, 28 (2): 205-212.   Abstract （1666）      PDF（pc） （7873KB）（1235）       Knowledge map    Save The MS 6.8 Bachu-Jiashi earthquake of Feb.24, 2003 occurred in the western Tarim Basin and is possibly the continuation of the Jiashi strong earthquake swarms in 1997-1998. However, its focal mechanism and rupture process are different from that of the Jiashi strong earthquake swarms, according to our preliminary study on its seismic tectonics with geomorphologic information from satellite images, the deep structures from the petroleum seismic exploration, the macro damage and isoseismic features from field investigation, the relocation of the epicenters of the aftershocks, and the regional seismic tectonics from both deep and surface tectonics. The occurrence of the MS 6.8 Bachu-Jiashi earthquake is closely related with the revealed reverse fault on the Maigaiti slope belt between the Bachu uplift and Kashi depression in western Tarim Basin. The sites of the ground fissures found in the field fit with the revealed reverse fault. Isoseismal features are also corresponding to the rupture direction of the fault. These evidences indicate that the MS 6.8 Bachu-Jiashi earthquake is the result of the southward rupturing from deep to shallow along a north-dipping reverse fault in Tarim Basin. This reverse fault is possibly the result of the propagation of the thrust fault-fold system named Kalpintag thrust belt in the front of Tianshan. Related Articles | Metrics

Select

EFFECT OF ROCK STRUCTURE ON STATISTIC CHARACTERISTICS OF ACOUSTIC EMISSION Liu Liqiang, Ma Shengli, Ma Jin, Lei Xinglin, Kusunose K, Nishizawa O, Jouniaux L SEISMOLOGY AND GEOLOGY    1999, 21 (4): 377-386.   Abstract （1461）      PDF（pc） （5435KB）（1361）       Knowledge map    Save A comparative study on acoustic emission during deformation of two kinds of granites with different structures under triaxial compression is performed by using a new acoustic emission recording system with fullwaveform record and broaddynamic range. One is Inada aplitegranite of homogeneous structure from Japan and the other is Mayet granite with cemented natural joints from France. For the former granite, acoustic emission events are dispersed randomly and there is no clearly clustering along the major fracture. For the latter granite, acoustic emission events are mainly concentrated nearby the joint. Acoustic emission events occur synchronously with the volumetric dilatation in the former one but far earlier than the volumetric dilatation in the latter one. The two kinds of granite are also clearly different in the frequency spectrum of acoustic emission. The former has narrower frequency band and more highfrequency component, while the latter has wider frequency band and generally lower frequency spectrum. In frequencyenergy relation, the number of acoustic emission events in the former shows a welllinear progressive relation from highenergy level to lowenergy level and it shows an apparent intermittent or nonlinear variation in the middlehigh energy interval, with higher proportion of large events. It indicates that the rock structure has an apparent controlling role in the basic statistic characteristics of acoustic emission events. The cause for the phenomena may be that the different rock structures result in different deformation modes and processes. Related Articles | Metrics