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MODERATE-STRONG EARTHQUAKES AND THEIR TECTONIC CORRELATION IN THE LIAODONG PENINSULA WAN Bo, JIA Li-hua, DAI Ying-lei, SUO Rui SEISMOLOGY AND GEOLOGY    2013, 35 (2): 300-314.   DOI: 10.3969/j.issn.0253-4967.2013.02.009 Abstract （1625）      PDF（pc） （3683KB）（9741259）       Knowledge map    Save Moderate-strong earthquakes happened very frequently in the Liaodong peninsula. In addition to the Haicheng M7.3 earthquake in 1975,there are also 19 earthquakes of M≥5 recorded in this area. The earthquakes are distributed regularly,mainly restricted to seismic belts or to the grid nodes. The spatial distribution is accordant to the NE-NNE trending faults such as the Jinzhou Fault,the Yalujiang Fault,and to the NW-trending conjugated ones. Moderate-strong earthquakes happened mostly near the tectonic basins where two sets of faults intersect,or close to the NW-trending tectonic belt. The NE-NNE and NW-trending faults are a pair of conjugate sheer fracture planes characterized mainly by lateral strike-slip movement under the action of the contemporary NEE-directed near-horizontal principal stress. The NE-NNE faults belong to the inheritance fault,which control the regional geological tectonic pattern and its evolution,often large in size; while the NW ones mostly belong to newly-generated fault,and their size is usually related to the size of NE-NNE faults they conjugate with. The study shows that the moderate-strong earthquakes in the Liaodong peninsula are controlled mainly by the NE-NNE structures,and the seismogenic structures are basically the NW faults. Meanwhile,correlated with the size of the NW faults,the moderate-strong earthquake activities show a trend of decreasing gradually from north to south and from west to east,and the magnitude of them decreases roughly from M7～7.5 to M5.5～6 or so. Reference | Related Articles | Metrics

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DEFORMATIONAL CHARACTERISTICS OF THE NIUSHOUSHAN-LUOSHAN FAULT ZONE AND ITS TECTONIC IMPLICATIONS WANG Wei-tao, ZHANG Pei-zhen, LEI Qi-yun SEISMOLOGY AND GEOLOGY    2013, 35 (2): 195-207.   DOI: 10.3969/j.issn.0253-4967.2013.02.001 Abstract （1843）      PDF（pc） （5826KB）（37384）       Knowledge map    Save As the outermost fault zone in the northeastern margin of the Tibetan plateau,the deep structures,distribution,movement feature and deformational mechanism of the Niushoushan-Luoshan Fault zone are crucial to understand the formation and evolution of the arcuate fault zones in the northeast corner of the Tibetan plateau. In this paper,we analyze four seismic reflection sections across the Niushoushan-Luoshan Fault zone and map in detail the area within the fault zone. These data indicate that the Niushoushan-Luoshan Fault zone is a discrete fault zone. The fault zone can be subdivided into three parts: the south part,i.e.the Luoshan Fault,is characterized by positive flower structure,shown as remarkable right lateral strike-slip; in the middle segment,that is,the Niushoushan Fault,no active fault exists on the east flank of the Niushoushan,and this region is dominated by intensive folding; the north part,the Sanguankou Fault,is a left-lateral strike-slip fault. The discontinuity and segmentation feature of the Niushoushan-Luoshan Fault zone suggest different deformational styles in different locations of the fault zone associated with the process of northeastward propagation of the Tibetan plateau. Reference | Related Articles | Metrics

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VOLCANIC THREAT LEVELS AND CLASSIFICATION OF VOLCANIC ACTIVITY IN CHINA HONG Han-jing, WU Jian-ping, WANG Qing-liang, LI Ke, ZHAO Ci-ping, SHANGGUAN Zhi-guan, YANG Qing-fu, ZHANG Heng-rong, LIU Guo-ming SEISMOLOGY AND EGOLOGY    2007, 29 (3): 447-458.   Abstract （3569）      PDF（pc） （1484KB）（32683）       Knowledge map    Save Although volcano erupting has not been recorded in Chinese continent during recent years,there are 15 Holocene volcanoes in Chinese continent,and some disturbance signals were reported from some volcanoes in China.Strong hydrothermal activities occurred in Tengchong volcano,some hydrothermal explosions even took place since 1993.Seismic activity in Changbaishan Tianchi volcano has been getting strong remarkably since July of 2002,accompanied with significant surface uplift and geochemical anomalies.Estimation on volcanic threat level is the base of classification of active volcanoes.Based on the results of volcano monitoring and investigation in recent years,the volcanic threat levels and classification of active volcanoes in China continent are discussed in this paper.Based on the volcanic activity levels of the other countries,the volcano threat in China can be rated into 7 levels as safety,attention,stand by,alarm,threat,hazard and disaster,corresponding to the activity stages of dormancy,late-dormancy,disturbance,unrest,being critical,irreversible and violent,respectively.Based on the dangerous levels of volcanoes,the activity of volcanoes in Chinese continent can be classified into 4 kinds:(1)those in the active phase,such as Changbaishan volcano,which is in the process of disturbance;(2)those with some evidences of activity,such as Tengchong volcano,which stays in the late-dormancy stage,but has the potential threat of eruption;(3)those with some possibility of potential eruption,including Wudalianchi,Jingpohu,Haikou volcanoes,where geophysical and geochemical observations all fall in the background category;and(4)those whose volcanism is unclear yet at present,such as Aer Shan,ErKe Shan,XiaoGulihe,Wulanhada,Keluo,Turphan,west Tianshan,Ashi,and Kekexili volcanoes. Related Articles | Metrics

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HOLOCENE PALEOSEISMOLOGY OF THE MIDDLE AND SOUTH SEGMENTS OF THE NORTH ZHONGTIAOSHAN FAULT ZONE, SHANXI WANG Yi-ran, LI You-li, YAN Dong-dong, LÜ|Sheng-hua, SI Su-pei SEISMOLOGY AND GEOLOGY    2015, 37 (1): 1-12.   DOI: 10.3969/j.issn.0253-4967.2015.01 Abstract （832）      PDF（pc） （4147KB）（28322）       Knowledge map    Save Shanxi Graben System(SGS)is a NNE-trending tectonic system located in the eastern and southern edges of Ordos Block and between Yinshan tectonic zone and Qinling tectonic zone. Composited with a series of NNE-, NE-trending graben basins, SGS is an important seismic zone in North China. Yuncheng Basin locates in the southern end of SGS, and is the deepest basin of the system. It is a half-graben with a shallow northern part and a deep southern part. As the south and east boundary of Yuncheng Basin, the North Zhongtiaoshan Fault Zone(NZFZ)played a key role in the development of the topology and tectonics setting of Yuncheng Basin. NZFZ is a normal fault zone, NE- to NEE-trending and 130km long. This fault zone can be divided into 3 segments: the south, the middle, and the north segment, and there are no historical M≥7, but only 3 M=6 have taken place. Previous study suggests that the tectonic activity in this area is low and the earthquake interval is relatively long; seismic activity in the north and south segments is the weakest: the earthquake recurrence interval in the north segment is >50ka and it has not been active for >50ka, the interval of the south segment is ～12ka and its last movement is about 7ka ago. Our work tells a different story: based on thorough fieldwork, satellite imagery analysis, and trench investigation, we found that there have been multiple earthquake events taking place in all of the 3 segments during Holocene. This study includes two trenches that locate in the south and middle segments of NZFZ, each of them renders 3 paleo-earthquake events: a 10 570～8 010a BP event, an around 6 670～6 550a BP event, and a 2 110～320a BP event in TC-1; a 7 930～11 300a BP event, a 4 800～6 010a BP event, and a 2 680a BP event in TC-2. Through comparing these events with other 2 trenches in the middle segment of NZFZ(a XTC trench that renders a 19 980a BP event and a 8 570～7 780a BP event with >2.2m vertical displacement; a XLC trench that renders a 8 980～7 340a BP event with ～1.8m vertical displacement), we identified: a 8 570～8 010a BP event which broke through both middle and south segment of NZFZ with a largest known vertical displacement of >2.2m and 95km surface rupture, a 4 800～6 010a BP and a 2 110～320a BP event with 7～30km surface ruptures and largest known vertical displacements of 0.7m and 1.2m, respectively. The recurrence interval of these events is about 3 500a. Calculated with empirical formula of normal fault in North China, the magnitude of the 8 570～8 010a BP earthquake should be at least 8.0, and the magnitudes of the 4 800～6 010a BP and 2 110～320a BP events are both ≈7.0. These findings suggest that, as a Holocene active fault zone which made up with multiple faults, the middle and south segments of NZFZ have shown strong seismic activity and have triggered multiple earthquake events during the Holocene. Contrary to previous study, the activity of south segment might not be the weakest, and it is possible that the south segment is more seismic active than the middle segment. Reference | Related Articles | Metrics

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LANDSLIDES TRIGGERED BY THE APRIL 20,2013 LUSHAN, SICHUAN PROVINCE MS 7.0 STRONG EARTHQUAKE OF CHINA XU Chong, XU Xi-wei, ZHENG Wen-jun, WEI Zhan-yu, TAN Xi-bin, HAN Zhu-jun, LI Chuan-you, LIANG Ming-jian, LI Zhi-qiang, WANG Hu, WANG Ming-ming, REN Jun-jie, ZHANG Shi-min, HE Zhong-tai SEISMOLOGY AND GEOLOGY    2013, 35 (3): 641-660.   DOI: 10.3969/j.issn.0253-4967.2013.03.018 Abstract （2420）      PDF（pc） （13051KB）（11728）       Knowledge map    Save On April 20,2013,a strong earthquake of MS 7.0 struck the Lushan County,Sichuan Province of China. In this paper,basic information of the April 20,2013 Lushan earthquake,historical earthquakes in the Lushan earthquake struck area and associated historical earthquake-triggered landslides were introduced firstly. We delineated the probable spatial distribution boundary of landslides triggered by the Lushan earthquake based on correlations between the 2008 Wenchuan earthquake-triggered landslides and associated peak ground acceleration(PGA).According to earthquake-triggered landslides classification principles,landslides triggered by the earthquake are divided into three main categories: disrupted landslides,coherent landslides,and flow landslides. The first main category includes five types: rock falls,disrupted rock slides,rock avalanches,soil falls,and disrupted soil slides. The second main category includes two types of soil slumps and slow earth flows. The type of flow landslides is mainly rapid flow slides. Three disrupted landslides,including rock falls,disrupted rock slides,and soil falls are the most common types of landslides triggered by the earthquake. We preliminary mapped 3883 landslides based on available high-resolution aerial photographs taken soon after the earthquake. In addition,the effect of aftershocks on the landslides,comparisons of landslides triggered by the Lushan earthquake with landslides triggered by other earthquake events,and guidance for subsequent landslides detailed interpretation based on high-resolution remote sensing images were discussed respectively. In conclusion,based on quick field investigations to the Lushan earthquake,the classifications,morphology of source area,motion and accumulation area of many earthquake-triggered landslides were recorded before the landslide might be reconstructed by human factors,aftershocks,and rainfall etc. It has important significance to earthquake-triggered landslide hazard mitigation in earthquake struck area and the scientific research of subsequent landslides related to the Lushan earthquake. Reference | Related Articles | Metrics

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THE RE-VERIFICATION OF CHANGDE,HUNAN,EARTHQUAKE IN 1631 DONG Rui-Shu, ZHOU Qing, CHEN Xiao-Li, DU Long, YU Hong-mei SEISMOLOGY AND GEOLOGY    2009, 31 (1): 162-173.   DOI: 10.3969/j.issn.0253-4967.2009.01.015 Abstract （3581）      PDF（pc） （2305KB）（11541）       Knowledge map    Save A destructive earthquake occurred around Changde,Hunan Province,south-central China in 1631.The previous research of this earthquake yielded 4 different epicenter locations and isoseismal intensity maps.The authors replotted the isoseismals of this event based on checking historical earthquake records,in which the intensity value of the innermost isoseismal is Ⅷ.We concluded that the depth of this earthquake is from 15km to 18km.The basic considerations of our conclusion are as follows:a.This earthquake occurred in an area of lacustrine and fluvial deposits,with the magnitude of M 61/2;b.The geometrical center of the innermost isoseismal is the epicenter;c.The depth of epicenter is about 15 to 18km,which is based on the statistical relation between magnitude,depth of the earthquake source and epicenter intensity as well as Xie's statistical result.Finally,the authors discussed the influences of different ground conditions on the textual research and identification of historical data. Related Articles | Metrics

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EVIDENCE OF THE DONGBEIWANG-XIAOTANGSHAN FAULT IN BEIJING HE Zhong-tai, MA Bao-qi, LU Hai-feng, WANG Jin-yan SEISMOLOGY AND GEOLOGY    2009, 31 (2): 233-246.   DOI: 10.3969/j.issn.0253-4967.2009.02.004 Abstract （3059）      PDF（pc） （11224KB）（11382）       Knowledge map    Save Lots of different ideas stay on whether the Dongbeiwang-Xiaotangshan Fault in the northwest of Beijing exists or how it displays and acts.This paper analyzes the present seismic prospecting data and drill logs from exploration of active faults in Beijing urban areas,and reaches conclusion that the Dongbeiwang-Xiaotangshan Fault does exist as a subsurface fault and it is 40km long,trending NNE.Divided by the Nankou-Sunhe Fault,we name its northeast segment as the Xiaotangshan Fault and the southwest segment as the Dongbeiwang Fault.The Xiaotangshan Fault is active in early Pleistocene but not in middle Pleistocene.The Dongbeiwang Fault is active in the end of mid-Pleistocene but not in late Pleistocene. Related Articles | Metrics

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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 （1327）      PDF（pc） （5689KB）（11108）       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

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RIVER OFFSET AND SLIP RATE OF THE EAST SEGMENT OF ALTUN TAGH FAULT ZONE SINCE QUATERNARY Xiang Hongfa, Guo Shunmin, Zhang Wanxia, Zhang Bingliang SEISMOLOGY AND EGOLOGY    2000, 22 (2): 129-138.   Abstract （1745）      PDF（pc） （3885KB）（10376）       Knowledge map    Save Based on the gradation of stream and ridge offset and the dating of terrace sediments in a distance of 150km from Hongyaza in the west of Akesai eastward to Subei and Hongliuxiakou, the river offsets in Quaternary can be divided into 8 grades and their formation dates are acquired. The fault slip rates in different segments range 4.7～6.7mm/a. The average value is 6.0mm/a. As to the local section in a short period, the maximum slip rate can be 7.7mm/a. The distribution of offsets and slip rates shows that they are large at the middle and small at the ends, which may demonstrates that rupture initiates from the middle and develops towards the ends. The slip rate in Pliocene is larger than other epoches, which may be related to the quick lifting of Qinghai-Tibetan block since 5Ma B.P. and the large scale of escaping. Data show that fault rupture begins at the main fault, then extends to the vicinity and goes back the main fault. Related Articles | Metrics

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THE ACTIVITY AGE OF TARWAN FAULT AND GENESIS OF THE TOPOGRAPHIC SCARP CHEN Tao, LIU Yu-gang, MIN Wei, ZHOU Ben-gang SEISMOLOGY AND GEOLOGY    2012, (3): 401-414.   Abstract （1577）      PDF（pc） （10615KB）（9844）       Knowledge map    Save Many NW-trending faults have been developed on the north of the eastern segment of Altyn Tagh Fault. The Tarwan Fault,about 10km long and striking NW on the whole,is the western segment of the largest Tarwan-Dengdengshan-Chijiaciwo Fault among these faults. The fault appears as a straight linear scarp in the satellite image and a geomorphic scarp of dozens of centimeters to 5 meters high,topographically. The scarp dips NE and is composed mainly of beds of early Pleistocene conglomerate and Holocene aeolian sandy soil. As revealed by a measured topographic profile,the scarp composed of Holocene aeolian sandy soil is about 5m high,and that of early Pleistoscene conglomerate is about 1m high. Field investigation and trenches excavated on the vertical scarp have revealed the Tarwan Fault is a thrust fault,striking NW and dipping SW.The Geogene mudstone is thrust over the early Pleistocene conglomerate,with a throw of 0.5m. The Holocene aeolian sand and late Pleistocene gravel layers overlying the fault are not dislocated. The hanging wall of the fault is Geogene mudstone with rich groundwater and well-developed vegetation. Due to the protection and control of sand movement with vegetation,aeolian sand was accumulated constantly and preserved,and as a result,the aeolian sand layer became higher gradually. The foot wall of the fault consists of a Gobi gravel layer of a few centimeters thick on the surface and hard cemented conglomerate of early Pleistocene under it,with groundwater and vegetation being undeveloped. Therefore,Holocene aeolian sand is only developed on the hanging wall of the fault,and there is no Holocene stratum developed in the footwall. The height of the scarp formed on the early Pleistocene conglomerate is far lower than that on the Holocene aeolian sand. These findings indicate that the topographic scarp composed of Holocene aeolian sand was produced by external dynamic process rather than faulting,and that the Tarwan Fault is an early-middle Pleistocene thrust fault. Reference | Related Articles | Metrics

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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 （2937）      PDF（pc） （434KB）（9254）       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

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WATER VAPOR ANOMALIES RELATED TO THE LUSHAN AND WENCHUAN EARTHQUAKES IN THE LONGMENSHAN MOUNTAINS AREA DENG Zhi-hui, CHEN Mei-hua, YANG Zhu-zhuan, YAN Xing, DENG Yuan-li SEISMOLOGY AND GEOLOGY    2014, 36 (3): 658-666.   DOI: 10.3969/j.issn.0253-4967.2014.03.009 Abstract （1257）      PDF（pc） （2906KB）（8940）       Knowledge map    Save Studies of air relative humidity dynamic process in Longmenshan Mountains area, Sichuan, southwestern China show that, before the 2013 Lushan MS7.0 earthquake and the 2008 Wenchuan MS8.0 earthquake, the annual frequency of air relative humidity anomalies appeared to decrease year by year in the initial period, and then increased quickly. The fall time is longer, often more than 10 years, and the rise time is short, about 1～2 years. The epicenters are located in or near the area where the anomaly frequency of air relative humidity declined most and increased more than other regions. The tendency transition of the annual frequency of air relative humidity anomalies in the middle-term period of earthquake preparation is probably due to the opening and closing of rock fracture, underground fluid movement and geothermal energy release, which cause the change of ground temperature and latent heat exchange rate. In the medium and long-term period of earthquake preparation(10 to several years), the crust rock is under compression deformation, the rock pores and fissures are continuously closed or reduced, the releasing of underground hot water or hot vapor decreases, and the latent heat exchange rate has also decreased, therefore the relative humidity anomaly frequency shows a declining trend. Whereas in the medium and short-term period of the earthquake preparation, as the crustal rock deformation increases further, which may lead to micro fractures expanding, and the underground hot water and hot vapor by releasing will turn from decreasing to increasing, the latent heat exchange rate changes from reducing to rapidly increasing, and the relative humidity anomaly frequency also shows a transition from decreasing year by year to a rapid increase in burst. Reference | Related Articles | Metrics

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A STUDY ON THE ACTIVITY OF THE FAULTS AROUND AND THE LATE QUATERNARY TECTONIC FEATURES IN THE HANZHONG BASIN WANG Ming-ming, ZHOU Ben-gang, YANG Xiao-ping, LI Jiang-yi SEISMOLOGY AND GEOLOGY    2013, 35 (4): 778-792.   DOI: 10.3969/j.issn.0253-4967.2013.04.008 Abstract （1561）      PDF（pc） （11243KB）（7748）       Knowledge map    Save Since the Wenchuan earthquake,the seismic hazard of the northeastern segment of the Longmenshan Fault zone as well as the Hanzhong Basin has drawn more and more concerns. However,the essential data needed for further analysis on the seismic hazard in this region is scarce at present time,hence there is an urgent need for an in-depth study on the activities of faults around the basin. The faults around the Hanzhong Basin include five main faults,namely,the northern margin fault of Hanzhong Basin,the southern margin fault of Hanzhong Basin,the Qingchuan Fault,the Chaba-Lin'ansi Fault and the southern margin fault of Liangshan. Based on several detailed field investigations on the geometric distribution,movement nature and active ages of the five faults,and with consideration of previous work,our study shows that the late-Quaternary tectonic activity in the basin is relatively intense in west and weak in east. The west section of the north-margin fault of the Hanzhong Basin(east of Baohe)was active in early late Pleistocene,while its eastern section(west of Baohe)was active in middle Pleistocene. The south-margin fault of the basin was also active in middle Pleistocene. And the three faults in the southwest of the basin were all active in late Pleistocene. This activity pattern of high in the west and low in the east is also demonstrated by the difference in thickness of Quaternary system and the distribution of small earthquakes. Reference | Related Articles | Metrics

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CHARACTERISTICS OF MICROSTRUCTURES OF THE INVISIBLE FAULTS IN QUATERNARY UNCONSOLIDATED SEDIMENTS Chao Hongtai, Deng Qidong, Li Jialing, Wang Zhicai, Man Hongmin SEISMOLOGY AND EGOLOGY    2000, 22 (2): 147-154.   Abstract （1830）      PDF（pc） （2319KB）（7607）       Knowledge map    Save Invisible faults often developed in Quaternary unconsolidated sediments including concealed faults and die-out faults, which lead to complexity and multi-solution for paleoearthquake research. In this paper, original-state directional samples related to invisible or die-out faults are collected from some typical paleoearthquake profiles and solidified in laboratory. Microstructures have been observed after grinding slides in three-dimension coordinate system. Some indicators of invisible faults have been found in micrscopic field. The mechanisms of die-out faults have also been studied. It is suggested that according to microstructural observation, to confirm or negate the existence of concealed faults or to trace the terminated levels of die-out faults, can help us determine the age and periods of paleoearthquake events more accurately combining with macroscopic observation and age dating. Related Articles | Metrics

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ANALYSIS OF ELECTROMAGNETIC CO-SEISMIC PHENOMENA OBSERVED IN CSELF STATIONS HAN Bing, TANG Ji, ZHAO Guo-ze, WANG Li-feng, DONG Ze-yi, FAN Ye, SUN Gui-cheng SEISMOLOGY AND GEOLOGY    2022, 44 (3): 753-770.   DOI: 10.3969/j.issn.0253-4967.2022.03.012 Abstract （939）   HTML （154）    PDF（pc） （8002KB）（7332）       Knowledge map    Save With the support of the wireless electro-magnetic method(WEM)project, the control source extremely low frequency(CSELF)continuous observation network, which includes 30 electromagnetic stations in Beijing capital area(BCA)and the southern section of the North-South Seismic Belt in China, was built for recording the artificial and nature source singles. The natural source observation of the network was started in July 2013 and December 2013 in batches and the electromagnetic field was recorded continually with a sampling rate of 16Hz. Until now, the co-seismic electromagnetic signals have been recorded repeatedly in several stations. In this paper seven co-seismic electromagnetic signals recorded at Jinggu station and co-seismic electromagnetic signals associated with two strong earthquakes recorded at different stations surrounding the epicenter are studied. It is found that the variation of the EM filed is similar to the seismogram, and the amplitude of the co-seismic EM signal is much larger than the background signal generated by earth induction, and the intensity of the vertical magnetic field is about ten times as big as the horizontal electromagnetic field. For co-seismic EM signals recorded at the same station, the relationship between the amplitude of electromagnetic field and the magnitude of the earthquake is basically linear in logarithmic domain. Meanwhile, the amplitude of electromagnetic field is also affected by focal depth of the earthquake and distance between the stations and the epicenter. When the epicenter distance is close, the amplitude of the co-seismic signal caused by the earthquake with shallow focal depth is higher. When the focal depth is similar, the amplitude of electromagnetic co-seismic signal caused by the earthquake closer to the station is larger. For the co-seismic EM signals associated with a same earthquake recorded by different stations, the larger the epicenter distance is, the later the signal appears and the longer the duration is. However, the signal amplitude is not only affected by the epicenter distance, but also related to the near-surface medium at the observation point. The electromagnetic co-seismic signals observed at Dali station which is the farthest away from the epicenter of Jinggu earthquake show the characteristics of large amplitude, long duration, and low dominant frequency. This may be related to the electrical structure near the surface of Dali Platform. The electromagnetic field signals of the 5 components of Jinggu, Muding and Dali stations before and after the Jinggu earthquake of magnitude 5.9 were transformed by wavelet transform. Finally, the wavelet spectrum with the horizontal axis as time and the vertical axis as frequency was obtained to indicate the time-frequency changes of the abnormal electromagnetic signals of the same seismic wave. According to the wavelet analysis and combining with the time series before and after the Jinggu earthquake of MS5.9, the energy enhancement mainly occurs in the shear wave and surface wave periods, while the P-wave is not obvious in the wavelet energy spectrum due to its small amplitude, and only some weak enhancement with scattered frequency can be observed. The main frequency of electromagnetic co-seismic signal is between 1Hz and 2Hz. At the beginning of the co-seismic signal, there are high frequency components, and the high frequency gradually decreases with the increase of epicenter distance. Moreover, compared with electric field, magnetic field can record more abundant high-frequency information. This may have to do with different dominant mechanisms for electric and magnetic field generation. In this paper, several earthquakes recorded at Jinggu station and electromagnetic co-seismic phenomena caused by two strong earthquakes at Jinggu station are summarized and analyzed. The results show that the variation of co-seismic electromagnetic signal is very complicated, and its starting time, duration, amplitude, and frequency range have some rules, but some stations show their particularity under multiple seismic events, so it is difficult to discuss the mechanism of its generation. However, in terms of observation phenomena, the electromagnetic field variation data observed continuously by extremely low frequency stations give us a more comprehensive understanding of the Earth’s electromagnetic field itself and the electromagnetic signals related to earthquakes. The accumulation of more seismic-related electromagnetic phenomena and the support of theoretical simulation can deepen the understanding of electromagnetic field variation before, during and after the earthquake. Table and Figures | Reference | Related Articles | Metrics

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DETECTION OF SHALLOW SEDIMENTARY STRUCTURE IN SIYANG, JIANGSU PROVINCE BY MICROTREMOR H/V SPECTRAL RATIO METHOD PENG Fei, WANG Wei-jun, XIONG Ren-wei, LÜ Xiao-jian, YAN Kun, SUN Xin-zhe, GENG Shuang, KOU Hua-dong SEISMOLOGY AND GEOLOGY    2022, 44 (3): 561-577.   DOI: 10.3969/j.issn.0253-4967.2022.03.001 Abstract （1243）   HTML （184）    PDF（pc） （11673KB）（6966）       Knowledge map    Save Earthquake sources, wave propagation effects and site effects directly affect the structural damage during earthquakes. Among these factors, site effects amplify and prolong the strong vibrations, playing a very important role in many great earthquakes such as the 1985 M8.1 Mexican earthquake, the 2015 MW7.8 Gorkha, Nepal, earthquake and the 2016 MW7.8 Kaikōura, New Zealand, earthquake. Microtremor is a random, natural and permanent complex vibration composed of body waves and surface waves, in which the energy of surface waves accounts for more than 70% of the total energy. Due to the multiple reflection and refraction of the wave, microtremor accumulates information reflecting the inherent characteristics of the soil layer of the site during the propagation process. Microtremor H/V spectral ratio method is an effective way to assess the site effects. Compared to the traditional seismic surveys, the low-cost convenient observation and rapid surface detection are the advantages of this method. Its results can be used as basic data for future earthquake hazard evaluation and urban construction planning. Siyang in Jiangsu Province is located in Tanlu seismic zone. In the history, there were some large earthquakes on the Tanlu earthquake zone. Among them, the Tancheng M8.5 earthquake is about 110km from our study area, so there is a certain risk of earthquake disaster in this area. It is necessary to analyze the regional site effect and the distribution characteristics of the shallow sedimentary interfaces in detail. Site amplification effect is an important factor to aggravate earthquake hazard, which is closely related to the shallow structure. Based on 217 microtremor observations, we use H/V spectral ratio method to study the seismic site effect and the shallow sedimentary structure of Siyang. The results of H/V peak frequency distribution show that the resonance frequency of seismic site in Siyang study area is between 0.6~1.8Hz with obvious fluctuations. The corresponding shallow sedimentary thickness is between 30m and 200m, which gradually deepens on the east and west sides with a shallow central region. In particular, the central urban area is 30~70m thick and the southeast corner is the thickest. The shallow deposits show an obvious deep and shallow alternating band distribution in the NNE direction, consistent with the location and strike of the Haisi fault zone. The sedimentary structure of the soil layer obtained in this paper is basically the same as the geological structure, which can be verified with the results of the reflection seismic exploration profile. The comparison with two seismic exploration profiles for shallow reflection in the area shows that the bedrock shape obtained by the microtremor H/V spectral ratio method is reliable. Therefore, the sedimentary structure and site effect characteristics obtained by this method can provide useful reference for the microzoning of seismic risk in Siyang. Table and Figures | Reference | Related Articles | Metrics

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STUDY ON THE RELATIONSHIP BETWEEN THE RESERVOIR-INDUCED SEISMICITY AT ZIPINGPU RESERVOIR AND THE MS 8.0 WENCHUAN EARTHQUAKE MA Wen-tao, XU Chang-peng, ZHANG Xin-dong, XU Xi-wei, LI Hai-ou, YUAN Jing-li SEISMOLOGY AND GEOLOGY    2011, 33 (1): 175-190.   DOI: 10.3969/j.issn.0253-4967.2011.01.017 Abstract （4350）      PDF（pc） （1444KB）（6788）       Knowledge map    Save Using the observations of the Zipingpu reservoir seismic network(including seven short-period seismic stations,with an average station distance of 10km)of the period from July 2004 to 2009,and the data from January-December 2009 recorded by the intensive seismic observation network(six short-period seismic stations with the station spacing of 3km),930 foreshocks near Zipingpu reservoir,the main shock,and 5789aftershocks,as well as the initial rupture of the MS 8.0 Wenchuan earthquake were relocated with double difference location algorithm.Combined with the geological field investigations,the analysis of seismic activity in Zipingpu reservoir area,the distribution of coseismic surface rupture,the depth of initial rupture location of Wenchuan MS 8.0 earthquake,and the aftershock distribution,we find that the occurrence of MS 8.0 Wenchuan earthquake has close relation with Zipingpu reservoir: 1) The seismic swarms at the Shuimo,and Dujiangyan and Shenxigou area are 10 kilometers away from the reservoir,the seismic strain release caused by Zipingpu reservoir increased by 200%,and the release was closely related to water level changes and accelerated before the Wenchuan earthquake; 2) There are two northeast directed coseismic surface rupture zones with 1m displacement along Zhongtanpu Fault; 3) the aftershocks of Wenchuan earthquakes are mainly distributed on northwestern wall of the Zhongtanpu Fault; 4) The relocation revealed that the Wenchuan earthquake occurred at 27minutes,59.5 seconds,the depth is between 6～9km; and 5) by comparison,the focal depths of the fore-shocks occurring on 2008-04-05 are about 7.8km,and the initial time of waveforms of this swarm is same as that of the MS 8.0 Wenchuan earthquake. Reference | Related Articles | Metrics

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ACTIVITY AND SLIP RATE OF THE NORTHERN SECTION OF YELLOW RIVER FAULT REVEALED BY DRILLING LEI Qi-yun, CHAI Chi-zhang, ZHENG Wen-jun, DU Peng, XIE Xiao-feng, WANG Yin, CUI Jin, MENG Guang-kui SEISMOLOGY AND GEOLOGY    2014, 36 (2): 464-477.   DOI: 10.3969/j.issn.0253-4967.2014.02.015 Abstract （703）      PDF（pc） （5772KB）（6289）       Knowledge map    Save Yellow River Fault is the longest, deepest fault in the Yinchuan Basin, also is the eastern boundary of the basin. Because its north section is buried, its activity and slip rate remains unknown, which made a negative impact on understanding the evolution and seismic hazard of the Yinchuan Basin. In this study, a composite drilling section with a row of drillholes were laid out along the northern section of the Yellow River Fault based on the results of shallow seismic exploration near the Taole Town, where oil seismic exploration data are available. Fault activity and slip rate are obtained by measuring the age of samples of holes. The results show that the northern section of the Yellow River Fault is a late Pleistocene or Holocene Fault, its accumulative displacement is 0.96m since (28.16±0.12)ka BP, with an average slip rate of 0.04mm/a, which is significantly lower than the southern section. The activity intensity of the northern section of the Yellow River Fault is significantly lower than the southern section since Late Quaternary. In the Yinchuan Basin, the Helanshan eastern piedmont fault is the most active fault since late Quaternary, next is the Yellow River Fault, then, the Yinchuan buried fault and Luhuatai buried fault. Although the Yellow River Fault is the deepest and the longest fault, its maximum potential earthquake is magnitude 7, this seismogenic capability is weaker than the relatively shallower Helanshan eastern piedmont fault, on which occurred the Pingluo M8 earthquake in 1739 AD. Yinchuan Basin is the result of long-term activities of the four major faults, which shaped the special structure of the different parts of Yinchuan Basin. The Yellow River Fault controlled the evolution of the south part of Yinchuan Basin. The two-layer crustal stretching model can help us understand the structural deformation between the upper crust and the lower crust beneath Yinchuan Basin. Deformation of the upper crust is controlled by several brittle normal faults, while the deformation of the lower crust is controlled by two ductile shear zones. The shear sliding on Conrad discontinuity coordinates the extensional deformation of different mechanical properties between the upper and the lower crust. Yellow River Fault might have cut deeply into the Moho in Mesozoic, the tectonic activity in Yinchuan Basin began to migrate and was partitioned into several faults since the beginning of the Cenozoic, mainly in the Helanshan eastern piedmont fault. This may be the reason why the Yellow River Fault has lower seismogenic capability than the shallower Helanshan eastern piedmont fault. Reference | Related Articles | Metrics

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DISCUSSION ON BLOCK KINEMATIC MODEL AND FUTURE THEMED AREAS FOR EARTHQUAKE OCCURRENCE IN THE TIBETAN PLATEAU: INSPIRATION FROM THE LUDIAN AND JINGGU EARTHQUAKES XU Xi-wei, CHENG Jia, XU Cong, LI Xi, YU Gui-hua, CHEN Gui-hua, TAN Xi-bin, WU Xi-yan SEISMOLOGY AND GEOLOGY    2014, 36 (4): 1116-1134.   DOI: 10.3969/j.issn.0253-4967.2014.04.015 Abstract （1635）      PDF（pc） （11867KB）（5598）       Knowledge map    Save By use of existing active faults, GPS monitoring data and other information and supposing a block-like motion, the Tibetan Plateau can be divided into multiple first-order and second-order blocks in accordance with basic definition of active block, and the block kinematic model with slip vector is given. Then by analysis of the relationship between the earthquake series, including the 2014 Ludian and Jinggu earthquakes, occurring in the Tibetan Plateau in the past more than a decade and the block motion, the themed areas for future surface rupturing earthquakes are determined to be related to the eastward or southeastward motion of the Bayan Har and Qiangtang blocks. The risk fault segments for the future earthquakes may include the southeastern segment of the Xianshuihe Fault, the Anninghe Fault, the Daliangshan Fault, the southern segment of the Xiaojiang Fault and the southeastern segment of the Red River Fault as well as the Maqin-Maqu segment of the eastern Kunlun Fault. In the earthquake monitoring and prediction tests, attention should be paid to the different structural strain patterns around the specific block boundary faults. Reference | Related Articles | Metrics

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COMPARATIVE EXPERIMENT ON SEISMIC SOURCES IN HIGH-RESOLUTION SEISMIC EXPLORATION FOR URBAN ACTIVE FAULTS PAN Ji-shun, LIU Bao-jin, ZHU Jin-fang, ZHANG Xian-kang, FANG Sheng-ming, WANG Fu-yun, DUAN Yong-hong, XU Zhao-fan SEISMOLOGY AND GEOLOGY    2002, 24 (4): 533-541.   Abstract （2687）      PDF（pc） （5549KB）（5282）       Knowledge map    Save Research on a large number of seismic events at home and abroad has indicated that tremendous earthquake hazards in urban areas are mostly attributed to earthquakes caused by active faults buried beneath the cities. The identification of urban buried active faults, therefore, is an important and urgent task. High-resolution seismic exploration is an effective geophysical technique that can be used to identify urban buried active fault at present. High-resolution seismic exploration for urban buried active faults is a sophisticated and systematic project, which involves excitation and receiving techniques, observational system, as well as seismic data processing and interpretation. The seismic source is of the first importance among the other problems that should be solved during the exploration. High-resolution seismic exploration for urban active fault calls for specific performance of the seismic source, because of peculiar environment in urban areas and particular characteristics of urban buried faults. For examples, relatively small offset of the fault requires a wider source spectrum, while strong disturbances in urban areas need a higher anti-jamming capability of the source. A comparative experiment on various types of sources, including vibroseis, vacuum accelerating weight drop, hammer-blow, air gun and explosive is carried out along the traverse across the Bayishuiku Fault. The features of various source spectrums are obtained by using spectrum analysis technique. The comparison of time-stacked sections obtained by using vibroseis, vacuum accelerating weight-drop and hammer blow from the traverse across the Bayishuiku Fault in Fuzhou City is presented in this paper. The effectiveness of various seismic sources in the exploration of urban buried active faults is discussed in detail. Related Articles | Metrics

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A REVIEW ON THE RESEARCH OF ACTIVE TECTONICS——HISTORY, PROGRESS AND SUGGESTIONS DENG Qi-dong, WEN Xue-ze SEISMOLOGY AND GEOLOGY    2008, 30 (1): 1-30.   Abstract （1890）      PDF（pc） （759KB）（5148）       Knowledge map    Save This paper reviews the history and progresses of the research on active tectonics in China and overseas. By giving a brief introduction on histories of active tectonic researches in China and some other countries,the paper sums up the process and development on the quantitative investigation of active tectonics since the 1980's,and puts the focus on the main efforts and progresses that have been made in China on some aspects of the research,such as the basic survey and research and the applied investigation of active tectonics,the study on theories about regional active tectonics and their kinematics and geodynamics,the survey on the coupling relations between deep and shallow structures,the project on active fault survey and prospecting and seismic hazard assessment in urban areas,as well as the efforts on using the Quaternary geochronology. Further,the paper looks back to the Chinese efforts on the quantitative investigation of active tectonics,sums up those cognitions from studies on the determination of several basic and measurable parameters of active tectonics,such as the length of fault and fault-segment,coseismic slip and cumulative slip,fault slip rate,sequence of paleo-earthquake events,and the time elapsed from the latest event. At the same time,efforts and progresses in China on assessing long-term seismic potential for active fault and evaluating potential risk from potential active fault movement have been reviewed by summarizing researches on developing theories,models,methods and on application to the probabilistic assessment of time-dependent seismic potential,magnitude estimation for potential earthquake on active fault,and forecasting the potential risk caused by potential active fault movement. Finally,considering the realities and problems in the research of active tectonics in China,the authors put forward several suggestions for issues worthy of paying more attention to for further investigation in the future. Related Articles | Metrics

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GEOLOGICAL AND GEOMORPHIC EVIDENCE FOR THE QUATERNARY ACTIVITY ON THE NORTHEAST SEGMENT OF LONGMENSHAN FAULT ZONE YANG Xiao-ping, FENG Xi-jie, GE Tian-yong, SONG Fang-min, SHI Ya-qin, LIU Yu-fa SEISMOLOGY AND GEOLOGY    2008, 30 (3): 644-657.   Abstract （2742）      PDF（pc） （2007KB）（4902）       Knowledge map    Save The Longmenshan Fault zone is an important thrust belt on the eastern margin of the Qinghai-Tibet Plateau,consisting of the back-range,the central and the front-range faults,which differ from each other in size and activity.The rupture zone of the Wenchuan earthquake of 12 May 2008 occurred over a length of～270km along the Yingxiu-Beichuan Fault(a segment of the Central Fault)and a length of～70km along the Guanxian-Anxian Fault(a segment of the Front-Range Fault).The northern end of the fracture zone is at the Nanba region in Central Fault.In this work,we make a detailed field investigation on the northeast segment of the Longmenshan Fault zone.Qingchuan Fault is the northeast segment of the Longmenshan Back-range Fault,and the Chaba-Lin'ansi Fault is the northeast segment of the Longmenshan Central Fault.Along the above two faults,we make geological and geomorphologic mapping of Tuguanpu,Da'an and Hujiaba regions,where the Qingchuan Fault runs through the Tuguanpu and Da'an area,and Chaba-Lin'ansi Fault runs through the Hujiaba area.Based on the field investigation,there are five terraces in the northeast Longmenshan area along the major rivers.The height above the river of T1 terrace is about 3～5m,and the formation time is Holocene.The heights of T2 and T3 terraces are 10m and 30～35m above the river,and the deposition time of alluvium and diluvium is Late Pleistocence.The remnant of T4 terrace's sediment covers on some hills,with the height above the river of about 60～70m.In the remnant,granite cobble and sandstone cobbles have been air slaked,these gravels have the shapes only.T5 terrace's height is about 90m,the sediment on it has been eroded.Qingchuan Fault and Chaba-Lin'ansi Fault were strongly active faults in the times before T3 and after T4 formed.Some fault grooves were formed on T4 or T5 terrace,they have 30～180m in width,and 8～20m in depth.The vertical displacement of T4 terrace's gravels is 10～15m.Fault groove didn't form on T3 terrace,or the terrace height on a fault wall is consistent with other fault wall.At some places,T3 terrace's gravels overlie the fault zone. Related Articles | Metrics

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STUDY ON THE CHARACTERISTICS,MECHANISM, AND SPATIAL DISTRIBUTION OF YUSHU EARTHQUAKE TRIGGERED LANDSLIDES XU Chong, XU Xi-wei, YU Gui-hua SEISMOLOGY AND GEOLOGY    2012, 34 (1): 47-62.   DOI: 10.3969/j.issn.0253-4967.2012.01.006 Abstract （3133）      PDF（pc） （2059KB）（4853）       Knowledge map    Save On April 14,2010 at 07:49 (Beijing time), a catastrophic earthquake with MS 7.1 struck Yushu County, Qinghai Province, China. About 2036 landslides, covering an area of about 1.194km2, were interpreted from aerial photographs and remote sensing imageries and verified by field check. And based on the above, the spatial distribution of the Yushu earthquake triggered landslides is presented in this paper. The distribution of the landslides was strongly dominated by main surface ruptures, and their types are varied, with the collapse-type landslide as the dominant. There are five genetic mechanisms of Yushu earthquake triggered landslides, they are: the slope-toe excavation type, the surface water infiltration induced slope slip type, the fault dislocation type, the shaking type, and post-quake snow melting and rainfall penetration type. Besides the main seismic surface ruptures, there are many slope fissures developed mainly on the SE end of the surface rupture zone on the SW wall, an area undergoing intensive compression in the earthquake. Reference | Related Articles | Metrics

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A REVIEW OF THE THINKING AND PROCESS ABOUT PREDICTION OF LUSHAN M7.0 EARTHQUAKE ON APR. 20, 2013 SU Qin, YANG Yong-lin, ZHENG Bing, WANG Shuang-hong, LI Fei-fei, LIU Guan-zhong SEISMOLOGY AND GEOLOGY    2014, 36 (4): 1077-1093.   DOI: 10.3969/j.issn.0253-4967.2014.04.012 Abstract （1390）      PDF（pc） （13890KB）（4581）       Knowledge map    Save Before the Lushan M7.0 earthquake of April 20, 2013, fault displacement time histories inferred from near-field observation in Xianshuihe, Anninghe and Zemuhe Fault zones in Sichuan Province showed long-, mid-, and short-term anomalies which deviated from the normal background. The long-term anomalies were mainly represented by extensional faulting, the mid-term anomalies were marked mainly by turning of anomaly trends, and the short-term anomalies appeared mainly as compressional movement of the central-northern segment of Xianshuihe Fault. And based on these anomalies, a relatively accurate short-term prediction to this earthquake was proposed by the Survey Engineering Institute of Earthquake Administration of Sichuan Province. In this article, we summarize the thoughts and process of the prediction to Lushan earthquake, and present the bases and process for the long-, mid-, and short-term prediction. This experience can be useful for short-term prediction of strong earthquake in the future. Our preliminary results show that: 1)The sudden acceleration of variation in anomaly of short-baseline and short-leveling has short-term predictive significance to the origin time of strong earthquake. 2)Combined with analysis on the characteristics of time series of the occurrence time of cross-fault deformation anomalies, and the high gradient zones and their temporal evolutions revealed by mobile gravity surveys, we chose the intersection of the anomalous zones as the hazardous area and found it has a better predictive effect for determining the location of strong earthquake. 3)Statistical analysis shows that the duration of cross-fault deformation anomalies has certain significance for predicting the magnitude of strong earthquake. According to the characteristics of fault activity, the southeastward movement rate of the Bayar Har block may be greater than that of the eastern boundary of the Sichuan-Yunnan block before the Lushan earthquake, which aggravated the compressional and extensional movement of the northern segment of Longmenshan Fault, the middle-northern segment of Xianshuihe Fault and the Zemuhe Fault, and made the southern segment of Longmenshan Fault and the northern segment of Anninghe Fault locked. The faults differed remarkably in their activity patterns, which were mutually restrained and adjusted, as well as convertible. Thus, brittle rocks in the transition zone between plateau and basin ruptured and earthquake occurred. Currently, short-term earthquake prediction is still based on empirical results, and its scientificity is insufficient and pending further discussion. Reference | Related Articles | Metrics

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NEOTECTONICS AND KINEMETICS ALONG THE YABRAI RANGE-FRONT FAULT IN THE SOUTH ALASHAN BLOCK AND ITS IMPLICATIONS FOR REGIONAL TECTONICS YU Jing-xing, ZHENG Wen-jun, LEI Qi-yun, SHAO Yan-xiu, GE Wei-peng, MA Yan, LI You-juan SEISMOLOGY AND GEOLOGY    2013, 35 (4): 731-744.   DOI: 10.3969/j.issn.0253-4967.2013.04.004 Abstract （1543）      PDF（pc） （11842KB）（4571）       Knowledge map    Save The Yabrai range-front fault is a normal fault,which is about 120km long,trends N60°E and distributes along the southeast margin of the Alashan block. In this paper,we focus on the geomorphology and kinematics of the Yabrai range-front fault,and discuss the implications of the fault for the regional tectonics. This fault consists of three segments and the most active one is located in the southwest,which has a length of about 35km. The about 1～2m-high scarp,stretching almost the full segment,might be the result of the latest earthquake event. Fresh free surface indicates that the elapsed time of the last event should not be long. The middle segment is about 31km in length. The results suggest that just a single fault is developed along the piedmont of the Yabrai Shan,and there is no evidence of recent activity on this fault. In contrast to the simple geometric structure of the middle segment,the northeast segment consists of several faults. The scarps of the most recent earthquake event,which are clear but discontinuous,are about 0.5～1.5m high and some are up to 2m. Although the scarps along the southwest and northeast segments of the fault are similar,it is difficult to suggest they are caused by the same earthquake without precise dating. The seismic reflection profile suggests that the Yabrai range-front fault came into being as a normal fault in Cretaceous,when the Tibetan plateau did not emerge at that time. Therefore,we conclude that the Yabrai range-front fault is not the consequence of the Indo-Asian collision. But this region plays a great role in constraining the tectonic evolution of the Alashan block and therefore,the Tibetan plateau. Reference | Related Articles | Metrics

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LATE-QUATERNARY DEFORMATION AND GEOMORPHIC FEATURES ALONG THE LONGLING-RUILI FAULT HE Gen-wen, FU Bi-hong, LIU Ming, YANG Shun-hu, SHI Pi-long, LIU Feng SEISMOLOGY AND GEOLOGY    2014, 36 (2): 434-448.   DOI: 10.3969/j.issn.0253-4967.2014.02.013 Abstract （955）      PDF（pc） （10220KB）（4368）       Knowledge map    Save Longling-Ruili Fault zone(LRF)is located at the boundary between China and Burma, striking in northeast direction for about 135 km and controling the formation and evolution of Longling, Luxi, Zhefang and Ruili Basins. This study utilizes the high-resolution remote sensing data, such as ALOS and ASTER and SRTM digital elevation model data in combination with field work and RTK-GPS(Real Time Kinematic-Global Positioning System)to present the tectono-geomorphic features and geologic structures along the LRF. Analysis from the remote sensing data reveals that the LRF always develops along the south and north edges of the basins, and forms the NE-striking linear mountains and valleys between the basins, with a general strike in N55°E direction. In the field, many geomorphic features, including saddle-shaped landform, fault facets and shutter ridges, are developed along the LRF;While at Xintangfang and Ganlanpo, a several meters-wide shear zone crops out with fresh fault gouge. All the descriptions above demonstrate that the LRF is sinistral strike-slip fault and has been active since late Quaternary.To gain more insight into the activity of the LRF, a trench was excavated at Zhujiazhai which reveals the fresh fault plane at the base rocks and late Quaternary alluvial deposits above, but no evidence found indicating the fault offset those young deposits. Radiocarbon dating of charcoal samples from the bottom of alluvial fans indicates that there is no destructive earthquake happening along the north segment of LRF since 1150 B.P. Finally, analysis for the 1976 Longling earthquake and distribution of historical earthquake imply that the 1976 destructive earthquake may be triggered mostly by the NNW-striking newly formed fault zone rather than the NE Longling-Ruili Fault zone. Reference | Related Articles | Metrics

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SEISMOLOGY AND GEOLOGY    2011, 33 (1): 231-239.   Abstract （1029）      PDF（pc） （392KB）（4175）       Knowledge map    Save Related Articles | Metrics

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LANDSLIDES TRIGGERED BY THE 2013 MINXIAN-ZHANGXIAN, GANSU PROVINCE MS 6.6 EARTHQUAKE AND ITS TECTONIC ANALYSES XU Chong, XU Xi-wei, ZHENG Wen-jun, MIN Wei, REN Zhi-kun, LI Zhi-qiang SEISMOLOGY AND GEOLOGY    2013, 35 (3): 616-626.   DOI: 10.3969/j.issn.0253-4967.2013.03.015 Abstract （1437）      PDF（pc） （7043KB）（3882）       Knowledge map    Save On July 22,2013,an earthquake of MS 6.6 occurred at the boundary between Minxian County and Zhangxian County,Gansu Province of China. Many landslides were triggered by the earthquake and the landslides were of various types,mainly in falls,slides,and topples occurring on loess cliffs,and also including soil deep-seated coherent landslides,large-scale soil avalanches,and slopes with cracks. Most of the landslides were distributed in an elongated area of 250km2,parallels to the Lintan-Dangchang Fault, with about 40km in length and the largest width of 8km. Landslides occurrence shows obvious difference along the central line of the elongated area,corresponding to different characteristics of different segments of the seismogenic fault. The elongated landslides main distribution area and the location of the epicenter indicate that the direction of the fault rupture propagation is from southeast-east to northwest-west. Finally,two probable reasons causing the horizontal distance of about 10km between the central line of the elongated area and the Lintan-Dangchang Fault are presented. Reference | Related Articles | Metrics

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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 （4836）      PDF（pc） （49676KB）（3799）       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

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STUDY ON THE CRUSTAL THICKNESS BENEATH STATIONS OF SEISMIC NETWORK IN SHAANXI PROVINCE BY TELESEISMIC RECEIVER FUNCTION LIU Chun, CHONG Jia-jun, NI Si-dao, LI Shao-rui SEISMOLOGY AND GEOLOGY    2009, 31 (2): 313-320.   DOI: 10.3969/j.issn.0253-4967.2009.02.012 Abstract （3137）      PDF（pc） （1909KB）（3745）       Knowledge map    Save In this paper,we calculate receiver functions of body wave under the 14 stations in Shaanxi Province from 3-component digital waveform data of teleseismic earthquake events and obtain the thickness and Poisson ratio in crust of this area through H-kappa stacking.Through analysing the characteristics of crustal structure in Shaanxi Province,we discuss the relationship between seismic activity,crustal structure and geological structure in Shaanxi Province.The results show that(1)Crustal thickness in western Shaanxi is thicker than that in the east.Crustal thickness in the south and north of Shaanxi(≥40km)is larger than that in Weihe Basin,middle Shaanxi(about 34～40km).Among 14 stations,the crust beneath Huayin station is the thinnest(34km),which locates on the boundary between eastern Weihe Basin and Shanxi Province,and the biggest thickness(48km)appears beneath Longxian station at the northwestern end of Weihe Basin.(2)Poisson ratio in Shaanxi Province is about 0.24～0.29,which may be related to rock compositions.Poisson ratio in the north of Weihe Basin has higher values than those in the south.(3)There exist some relations between seismic activity and geological structure.The Weihe Basin with frequent earthquakes locates in a compound position of several tectonic systems.The Hanzhong Basin and Ankang Basin in the south of Shaanxi are controlled by several major faults,where the seismicity is relatively low.Seismic activity in northern Shaanxi is the lowest because of stable geological structure.Poisson ratio reflects material composition of earth interior.Our analysis suggests that seismic activity in the region with high Poisson ratio is higher than that with low Poisson ratio. Related Articles | Metrics

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THE PRELIMINARY STUDY ON SEISMOTECTONICS OF THE 2003 AD BACHU-JIASHI EARTHQUAKE (MS 6.8), SOUTHERN TIAN SHAN XU Xi-wei, ZHANG Xian-kang, RAN Yong-kang, CUI Xiao-feng, MA Wen-tao, SHEN Jun, YANG Xiao-ping, HAN Zhu-jun, SONG Fang-min, ZHANG Lan-feng SEISMOLOGY AND GEOLOGY    2006, 28 (2): 161-178.   Abstract （2688）      PDF（pc） （5675KB）（3676）       Knowledge map    Save Owing to strong and permanent Cenozoic re-orogenic processing, a lot of EW-striking active thrusts and folds have been developed in Tian Shan, resulting in crustal shortening in NS direction. There also exist NW-striking transform-like strike-slip faults that cut the Tian Shan and accommodate uneven crustal shortening larger in the west and smaller in the east. The seismogenic structures in and around the Tian Shan mainly include EW-striking thrust ramps or blind thrusts and NW-striking transform-like strike-slip faults. The 2003 AD Bachu-Jiashi earthquake is located at south of the Kalpintag nappe. A NE-trending deep seismic reflection profile about 50km long across the epicenter has been conducted after the earthquake. From this reflection profile four blind faults are identified. Together with earthquake relocation, these identified blind faults are used in the paper to interpret the seismogenic structures of the 1997 AD Jiashi strong earthquake swarm and 2003 AD Bachu-Jiashi earthquake. The 1997 AD Jiashi strong earthquakes were generated mainly by a NW-striking buried transform-like strike-slip fault, while the 2003 AD Bachu-jiashi earthquake by blind thrusts in front of the Kalpintag nappe. Related Articles | Metrics

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A PRELIMINARY STUDY ON PALEOEARTHQUAKES IN THE EASTERN KALPIN NAPPE SYSTEM,SOUTHWESTERN TIANSHAN,CHINA LI An, RAN Yong-kang, XU Liang-xin, LIU Hua-guo, LI Yan-bao SEISMOLOGY AND GEOLOGY    2011, 33 (4): 752-764.   DOI: 10.3969/j.issn.0253-4967.2011.04.002 Abstract （3539）      PDF（pc） （1033KB）（3661）       Knowledge map    Save There are several thrust-fold belts developed in the Kalpin nappe system of the southwestern Tianshan Mountains.Not only deformation rates of these thrust-fold belts are inconsistent,but also the paleoearthquakes recurrence laws on these thrust-fold belts in the nappe system are different.The Beichuan-Yingxiu Fault and the Pengguan Fault ruptured simultaneously in the Mw 7.9 Wenchuan earthquake.Therefore,it is worth discussing the question of how to determine the cascade-rupturing of a paleoearthquake on two or three thrust faults.We measured the scraps of different heights on the geomorphic surfaces(alluvial-proluvial fans)of different stages in eastern Kalpintage and Saergantage and analyzed the paleoearthquake events revealed by trenches in Shanchakou and Saergantage.Using the 10Be exposure age,we obtained the ages of the geomorphic surfaces.Then we got the upper and lower limit time of each paleoearthquake from the age of adjacent geomorphic surfaces.Finally,we got the recurrence intervals of different paleoearthquakes,the vertical dislocation of a single event,and the time range of the respective events.The results show that since 20ka BP,the average recurrence interval of paleoearthquake in the piedmont of east Kalpintage is 6.7±0.84ka,the vertical dislocation of a single event is 1m; the average recurrence interval of paleoearthquake in the piedmont of Saergantage is 5.4±0.50ka,and the vertical dislocation of a single event is 0.8～1.2m.The intensity of paleoseismicity is basically identical and the recurrence interval in Saergantage is slightly shorter.In the end,we discussed the possibility of cascade-rupturing accompanying these paleoearthquake events and found that the second and the third paleoearthquake events revealed by the trenches overlap in their occurrence time ranges,indicating the possibility of cascade-rupturing during the earthquake. Reference | Related Articles | Metrics

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AN INTRODUCTION TO THE GEODATABASE OF SCIENTIFIC INVESTIGATION OF THE MS8.0 WENCHUAN EARTHQUAKE LI Chen-xia, AN Yan-fen, YU Gui-hua, XU Xi-wei, CHEN Gui-hua, WANG Shi-yuan, GONG Hui-ling, YANG Hu, GUO Ting-ting, ZHANG Lan-feng SEISMOLOGY AND GEOLOGY    2008, 30 (3): 804-810.   Abstract （3325）      PDF（pc） （918KB）（3640）       Knowledge map    Save The geodatabase of scientific investigation of Wenchuan earthquake stores many field investigation data,such as the data of field geological survey sites,the surface rupture belts,the Quaternary faults in the earthquake region,paleoseismological trenches,folds,etc.Moreover,it includes some collection data,such as strata data,the catalog of the Wenchuan mainshock and aftershocks,the relocation catalog of aftershocks of the Wenchuan earthquake,the catalog of historical strong earthquake.The field data are recorded,edited,analysed,mapped and output with ArcGis,a powerful function in Gis software.The geodatabase of scientific investigation of MS8.0 Wenchuan earthquake was initially established,which includes the basic seismological information and realizes the integrated management of spatial location and attribute information.Data can be queried,analyzed and processed for the need of the correlation analysis of the data.Seismic tectonic map and surface rupture map can be drawn with the geodatabase,which can provide the basis for the determination of safety distance from the risky seismic rupture zones in post-disaster reconstruction and for the construction of the Wenchuan earthquake geographic information system. Related Articles | Metrics

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CRUSTAL STRUCTURES AND TECTONICS OF TANGSHAN EARTHQUAKE AREA: RESULTS FROM DEEP SEISMIC REFLECTION PROFILING LIU Bao-jin, QU Guo-sheng, SUN Ming-xin, LIU Kang, ZHAO Cheng-bin, XU Xi-wei, FENG Shao-ying, KOU Kun-peng SEISMOLOGY AND GEOLOGY    2011, 33 (4): 901-912.   DOI: 10.3969/j.issn.0253-4967.2011.04.014 Abstract （2584）      PDF（pc） （1180KB）（3608）       Knowledge map    Save On July 28,1976,the great Tangshan earthquake(M7.8)occurred in the Tangshan area of Hebei Province,which shocked the whole world.Before this earthquake,there was no earthquake with magnitude over M7.0 in this area.After this earthquake,the crustal structures and tectonics around Tangshan earthquake area remain unclear.In order to investigate the fine crustal structures,the main fault geometries and the relations between the deep-shallow tectonics in this area,a deep seismic reflection profiling with 40m receiver spacing and 200m shot spacing as well as 60-fold across the Tangshan Fault zone was carried out in the Fengnan region of Tangshan in 2009.Because our results have much higher spatial resolution than that of previous results of deep geophysical prospecting,some new features of the crustal structures and fault tectonics were revealed by this study.The results show that the thickness of the crust is about 32～34km along the profile,the Moho gradually deepens from east to west.Between Fengnan county and Xuanzhuang town,the reflections in the middle-lower crust and crust-mantle transitional zone are staggered by the deep Tangshan Fault,and dislocation occurs on the Moho on both sides of the deep fault,indicating the strike-slip effect of the deep Tangshan Fault.Tangshan Fault belt revealed by deep seismic reflection profile is a huge intra-continental strike-slip fault,and its shallow part appears as a typical flower-shaped structure,incising and disturbing the lower crust and crust-mantle transitional zone in the deep part.The complex faults and structures coexisting in both deep and shallow parts of the crust are the tectonic background for the Tangshan Earthquake,and also an important factor controlling the earthquake activity in the area. Reference | Related Articles | Metrics

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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 （3131）      PDF（pc） （9346KB）（3589）       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

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THE STRENGTH AND DEFORMATION MECHANISMS OF BRITTLE-PLASTIC TRANSITION ZONE, AND THE EFFECTS OF STRAIN RATE AND FLUIDS ZHANG Yuan-yuan, ZHOU Yong-sheng SEISMOLOGY AND GEOLOGY    2012, 34 (1): 172-194.   DOI: 10.3969/j.issn.0253-4967.2012.01.016 Abstract （2062）      PDF（pc） （930KB）（3509）       Knowledge map    Save Constraints provided by field observation, laboratory experiments and seismic data have lead to a general consensus that the shallow crust deforms by brittle faulting, while the lower crust deforms by crystal plastic flow. These constraints provide the basis for the dual mechanism model for the rheology of the crust and lithosphere in which the strength of the upper brittle crust is limited by Byerlee's law, while the strength of the lower ductile crust is limited by power law creep. The maximum depth of microseismic activity is controlled by the broad zone of brittle-plastic transition that lies between the two extreme brittle and plastic layers. While the dual mechanism model is so simple that overestimates the strength of rocks near the brittle-plastic transition zone. Although many studies about the deformation mechanism of brittle-plastic transition zone have been made, a 'flow law' representation, which can describe the strength for the brittle-plastic transition, has not been formulated, and there has been little research about fluid effects; In addition, research on brittle-plastic transition usually focuses on temperature effects, while the research on the aspects of strain rate and fluid are relatively weak. Studies of deformation mechanisms of minerals in faults have indicated that brittle-plastic transition of some faults occurred in the same depth (temperature and pressure) and this phenomenon, which has been considered to be relevant to synseismic loading and postseismic creep in earthquake cycles and confirmed by distribution of focal depth, is due to the strain rate. The presence of high-pressure fluid in active fault at depth is proved by analysis of characteristics of fault fluids, and these fluids, which can evolve in pressure pertaining to fracturing and sealing processes, play a key role during the seismic cycle. The formation of high-pressure fluid (cracks sealing) has several mechanisms, but researches show pressure solution deposition is one of the main mechanisms which controls crack sealing kinetics around active faults. Studies on pressure solution under the action of water can supplement and correct the crustal strength profile defined by traditional relations describing brittle/frictional behavior (Byerlee's law) and dislocation creep. As a consequence, we believe it is necessary to further study the impact of strain rate and fluid pressure on the brittle-plastic transition through deformation samples both from field and high-pressure high-temperature experiments. Simultaneously, we may establish the equation for the pressure solution to approximately estimate the strength of brittle-plastic transition zone. Reference | Related Articles | Metrics

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MOHR CIRCLES AND MAGNETOTELLURIC IMPEDANCE TENSOR INVARIANT ANALYSIS Jin Guangwen, Sun Jie, Jiang Zhao SEISMOLOGY AND GEOLOGY    1995, 17 (4): 439-445.   Abstract （2008）      PDF（pc） （829KB）（3505）       Knowledge map    Save Mohr circles and their application to Magnetotelluric(MT)impedance tensor analysis aredescribed in this paper,It iS illustrated that the rotational invariants of MT impedance tensors,having the advantages of providing variety of MT in a formation and stability,are frequently usedin MT data interpretation,Mohr circle,connecting the different forms of invariant impedancetensors,becomes an important graphic dignostic tool in studying MT impedance tensor properties.With the help of this powerful tool,some MT parameters,such as structural dimensional-ty,skewness,anisotropy,can be expressed visually and simply in the circle diagrams which giveimportant information for studying both vertical and lateral variation of the conductivity structures. Related Articles | Metrics

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DISCUSSION ON THE ISSUE OF PROPER DEPTH IN CALCULATING EQUIVALENT SHEAR WAVE VELOCITY FOR SITE CLASSIFICATION HUANG Ya-hong, L? Yue-jun, LAN Jing-yan, SHI Chun-hua, SHI Bing-xin SEISMOLOGY AND GEOLOGY    2010, 32 (2): 312-319.   DOI: 10.3969/j.issn.0253-4967.2010.02.014 Abstract （2373）      PDF（pc） （1288KB）（3455）       Knowledge map    Save Based on analysis of the shear wave velocity data of 823 boles from the northern,eastern,southern,northeastern and northwestern areas of China,we studied the difference of the equivalent shear wave velocities calculated with the soil-and-rock depths of 20m and 30m,respectively.We also discussed the features and differences among the Chinese,American and European seismic regulations in site classification using the parameter of equivalent shear wave velocities of boles.Our results indicated that:① The equivalent shear wave velocity will increase about 10 to 60m/s when we increase the calculation depth of soil-and-rock from 20m to 30m.The average increase is about 24m/s.② Comparing with the American and European seismic regulations,the current Chinese seismic regulation(GB 50011-2001)requires the information of the equivalent shear wave velocities calculated with the soil-and-rock depths of 20m,as well as the depth of the overburden in the site when classifying the site.However,it is usually difficult to obtain the usable overburden depth in many engineering sites to serve the site classification.Therefore,it is necessary for us to use for reference of American and European seismic regulations to increase the depth of soil-and-rock when calculating the equivalent shear wave velocity so as to get a more reliable parameter to serve for the site classification. Related Articles | Metrics

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ANALYSIS OF LANDSLIDES TRIGGERED BY WENCHUAN EARTHQUAKE CHEN Xiao-li, DENG Jian-liang, RAN Hong-liu SEISMOLOGY AND GEOLOGY    2011, 33 (1): 191-202.   DOI: 10.3969/j.issn.0253-4967.2011.01.018 Abstract （2432）      PDF（pc） （1021KB）（3360）       Knowledge map    Save On May 12,2008,a huge earthquake(MS=8.0)named Wenchuan earthquake hit Sichuan Province in Southwest China and triggered thousands of landslides.Post-seismic investigation and analysis discovered some characteristics of the landslides' spatial distribution.Landslides occurred unevenly on both sides of Longmenshan Fault zone,which are reverse faults and responsible for the Wenchuan earthquake.The majority of the landslides are distributed on the hanging wall of Longmenshan central fault,while only 12%of the total occurring on the footwall.The higher density of landslide is located at both ends of the Longmenshan Faults as well as the middle section.Statistical studies also show the occurrence of landslides has close relationship with ground motion,slope gradient and rock properties and so on.The geological background and evolution history of Wenchuan earthquake region have controlled the local geological and topographical setting and affected the landslide distribution when the great earthquake took place.Due to the exceptionally high topographic gradient and geological features such as loose soil and fragile rocks,this region is notoriously prone to landslide. Reference | Related Articles | Metrics

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TECTONICS, SCISMISITY AND DYNAMICS OF LONGMENSHAN MOUNTAINS AND ITS ADJACENT REGIONS Deng Qidong, Chen Shefa, Zhao Xiaolin SEISMOLOGY AND GEOLOGY    1994, 16 (4): 389-403.   Abstract （2688）      PDF（pc） （2637KB）（3335）       Knowledge map    Save The Longmenshan region inches the Longmenshan thrust belt,the western Sichuan foreland basin, the Longquanshan tectonic belt, and the Minshan uplift. The NE-trending Longmenshan thrust belt is composed of 4 major thusts and related napes, which form an extensive-compressive belt. The thrusting, mainly in a forward propagation style, started in the middle tolater part of Late Triassic and propagated from northwest to southeast. The Quaternary activity of the central and southern parts of the Longmenshan belt is stronger than the northern part.The western Sichuan foreland basin began to develop in the Late Triassic. The basin gradually retreated toward southwest since the late stage of Late Triassic, and the Quaternary deposition is limited on the Chengdu plain. The Longquanshan tectonic belt forms the eastern boundary of the foreland basin. It is a fault-propagation fold controlled by a master fault on its western margin.The NS-trending Minshan uplift northwest of the Longmenshan thrust belt is active since 2 Ma ago. The uplift is controlled by the Minjing and Huya faults, both with late Quaternary activities, on its western and eastern margins, respectively. The left-lateral slip rate of the Minjiang fault is about 1 mm/a. The Longmenshan thrust belt coincides with a steep gravity and magnetic gradient zone.The velocity structure and crustal thickness are very different on its northwestern and southeastern sides. There is a low velocity and high conductivity layer at a depth of 20 km on the west ofthe Longmenshan belt. The layer may be a detachment. Therefore, the Longmenshan belt maybe formed by a series of listric thrusts, and the wedges cut by the thrusts are thicker on the westand thinner on the east. The southern and central Longmenshan thrust belt and the Minshan uplift apparently control the seismicity in the region. This NE- to NS-trending seismic belt may be the active east-central margin of the Tibatan Plateau. Focal rnechanism solutions suggest that the principal compressive stress axis in the region trends NWW.The formation of the Longmenshan belt may be caused by the NW-SE directed compressionon the Songpan-Garze fold belt on the west. From Eocene to present, collision of the Indian and Eurasian plates caused southeastward movement of the western Sichuan block. This movementproduced a continuous compression on the Longmenshan belt. The movement of the westernSichuan block produced reverse faulting with left-lateral component on the boundary faults of the NS-trending Minshan uplift. The Quaternary activity in the northern part of Longmenshan beltis relatively weak due to the existence of the Minshan uplift. Related Articles | Metrics