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Source mechanism of strong aftershocks (M_s≥5.6) of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics

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Science china Earth Sciences 2009年第6期52卷 739-753页

作者： ZHENG Yong1,2,MA HongSheng3,Lü Jian4,NI SiDao5,LI YingChun6 & WEI ShengJi2 1 Institute of Geodesy and Geophysics,Chinese Academy of Sciences,Wuhan 430077,china 2 Institute of Geophysics,Chinese earthquake administration,Beijing 100086,china 3 Institute of earthquake Science,Chinese earthquake administration,Beijing 100086,china 4.earthquake administration of jiangxi province,nanchang 330039,china 5 School of Earth and Space Science,University of Science and Technology of china,Hefei 230026,china 6 earthquake administration of Jiangsu province,Nanjing 210014,china 1. Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China 2. Institute of Geophysics Chinese Earthquake Administration Beijing 100086 China 3. Institute of earthquake Science Chinese Earthquake Administration Beijing 100086 China 4. earthquake administration of jiangxi province Nanchang 330039 China 5. School of Earth and Space Science University of Science and Technology of China Hefei 230026 China 6. earthquake administration of Jiangsu province Nanjing 210014 China

Dozens of >M5, hundreds of >M4, and much more >M3 aftershocks occurred after the 2008/05/12 Wenchuan earthquake, which were well recorded by permanent and portable seismic stations. After relocated with P arrival, the >M3 aftershocks show two trends of distribution, with most of the aftershocks located along the north-east strike consistent with Longmenshan fault system, yet there is a north-west trend around the epicenter. It seems that substantially more aftershocks occur in regions with crystalline bedrocks. Then we collected waveform data from National Digital Seismograph Network and regional seismograph network of china, and employed 'Cut and Paste' method to obtain focal mechanisms and depths of the big aftershocks (M≥5.6). While most of those aftershocks show thrust mechanism, there are some strike slip earthquakes in the northern-most end of the rupture. Focal mechanisms show that the events located on the southern part of central Beichuan-Yingxiu Fault (BY) are mainly thrust earthquakes, which is consistent with initial mechanism of the main shock rupture. In the north part the aftershocks along the BY are also dominated by thrust slip, which is quite different from the right slip rupture of the main shock. Around Qingchuan-Pingwu Fault, the focal mechanisms are dominated by right-slip rupture with large depths (~18 km). So we suspected that in the north part the main shock might rupture on two faults: Beichuan Fault and Qingchuan-Pingwu Fault. The complex pattern of aftershock mechanisms argues for presence of a complicated fault system in the Longmenshan area.

关键词： focal mechanism seismotectonics Wenchuan earthquake cut and paste.

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The tectonic settings and seismogenic tectonics of the M5.7 Jiujiang earthquake in 2005,jiangxi province,china

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Science china Earth Sciences 2008年第5期51卷 640-653页

作者： LI ChuanYou1, ZENG XinFu2 & ZHANG JianXi3 1 Institute of Geology, china earthquake administration, Beijing 100029, china 2 jiangxi earthquake administration, nanchang 330039, china 3 Beijing earthquake administration, Beijing 100080, china 1. Institute of Geology China Earthquake Administration Beijing 100029 China 2. jiangxi earthquake administration Nanchang 330039 China 3. Beijing earthquake administration Beijing 100080 China

The M5.7 Jiujiang earthquake in 2005 was a mid-strong one, stronger than expected to occur in the region. This paper discusses the neo-tectonic settings of this earthquake, and it is thought that the earthquake region is located in the transitional belt, a potential area inducing weak to moderately strong earthquakes, between two large different tectonic units. The results of the reconnaissance work and on-the-spot investigation after earthquake indicate that the occurrence of the M5.7 Jiujiang earth- quake is closely related with the NE-trending fault on the western margin of Ruichang Basin. From its controlling to the landforms and Quaternary depositions, geological profiles, ESR dating, etc., the ac- tivity of the Dingjiashan-Langjunshan fault bounding the basin is discussed. It suggests that this fault displays an active one in Middle Pleistocene by the outcrop. Based on the activity of the fault, and the direction and location of the ground fissures, the isoseismal lines and the nodal plane of the focal mechanism solution, it is inferred that the Dingjiashan-Langjunshan fault is the seismogenic tectonics of the M5.7 Jiujiang earthquake, and the intersection point between this fault and the active NW ones is the possible origin of location of this earthquake. Our study shows that this earthquake is not an event exceeding expectation, and that the active and invisible characteristics of the causative fault are typical in the eastern area of china.

关键词： Jiujiang earthquake tectonic settings Dingjiashan-Langjunshan fault activity seismogenic tectonics

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Evolution of terraces Ⅰ–Ⅲ along the Anning River, western Sichuan, based on pollen records and terrace structure

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Science china Earth Sciences 2011年第1期54卷 127-135页

作者： CHENG JianWu1,2 1 Institute of Geology, china earthquake administration, Beijing 100039, china 2 earthquake administration of Gansu province, Lanzhou 730000, china Institute of Geology China Earthquake Administration Beijing China earthquake administration of Gansu province Lanzhou China

This study reconstructs the long-term evolution of river terraces over large spatial scales along the Anning River, western Sichuan, and identifies external factors controlling terrace formation. Pollen record analysis and terrace structure indicate that formation of the middle section of terraces I-III resulted from the interaction of changing climates and uplift of the margins of the Qinghai-Tibet Plateau. The relative influence of climate and uplift in terrace formation changes in different periods. The terraces reveal multiple, gradual uplift events on the eastern Qinghai-Tibet Plateau, which is of great significance for determining uplift mechanisms across the entire plateau.

关键词： Anning River in western Sichuan terrace formation pollen paleoclimate

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Deep tectonic setting of the 2008 Wenchuan M_s8.0 earthquake in southwestern china―Joint analysis of teleseismic P-wave receiver functions and Bouguer gravity anomalies

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Science china Earth Sciences 2009年第2期52卷 166-179页

作者： LOU Hai1, WANG ChunYong1, L ZhiYong2, YAO ZhiXiang1, DAI ShiGui2 & YOU HuiChuan1 1 Institute of Geophysics, china earthquake administration, Beijing 100081, china 2 earthquake administration of Sichuan province, Chengdu 610041, china 1. Institute of Geophysics China Earthquake Administration Beijing 100081 China 2. earthquake administration of Sichuan province Chengdu 610041 China

Teleseismic P-wave receiver functions at 20 broadband seismic stations in the Longmenshan fault zone (LMFZ) and its vicinity were extracted, and the crustal thickness and the P- and S-wave velocity ratio were calculated by use of the H-k stacking algorithm. With the results as constraints, the S-wave ve-locity structures beneath each station were determined by the inversion of receiver functions. The crustal structure of the Rear-range zone is similar to that of the Songpan-Garze Block, whereas the velocity structure of the Fore-range zone resembles that of Sichuan Basin, implying that the Central Principal Fault of LMFZ is the boundary between the eastern Tibetan Plateau and the Yangtze Block. Lower velocity zone exists in lower crust of the Songpan-Garze Block and the central-southern seg-ment of the Rear-range zone, which facilitates the detachment of the material in upper and middle crust. Joint analysis of the receiver functions and the Bouguer gravity anomalies supports the thesis on the detachment-thrust mode of the LMFZ. A double-detachment pattern is suggested to the tectonic setting in the Songpan-Garze Block. The upper detachment occurs at the depth of 10-15 km, and represents a high-temperature ductile shear zone. There is a lower detachment at the depth of about 30 km, below which the lower crust flow exists in the eastern Tibetan Plateau. Interpretation of the Bouguer gravity anomalies indicates that the Sichuan Basin is of higher density in upper and middle crust in compari-son with that of the Songpan-Garze Block. The LMFZ with higher density is the result from the thrusting of the Songpan-Garze Block over the Sichuan Basin. In the lower crust, higher P velocity and higher density in the Sichuan Basin are related to more rigid material, while lower S velocity and lower density in the Songpan-Garze Block are related to the softened and weakened material. The higher density block beneath the Sichuan Basin obstructs the eastward flow of lower crustal ma

关键词： Longmenshan fault zone (LMFZ) Wenchuan Ms8.0 earthquake deep tectonic setting teleseismic receiver function

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Joint exploration of crustal structure in Fuzhou basin and its vicinities by deep seismic reflection and high-resolution refraction as well as wide-angle reflection/refraction

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Science china Earth Sciences 2005年第7期48卷 925-938页

作者： ZHU Jinfang1, XU Xiwei2, ZHANG Xiankang3, HUANG Zonglin1, CHEN Xiangxiong1, FANG Shengming3, LIU Baojin3, ZHENG Rongzhang2,4 1. Seismological Bureau of Fujian province,Fuzhou 350003,china 2. Institute of Geology,china earthquake administration,Beijing 100029,china 3. Research Center for Exploration Geophysics,china earthquake administration,Zhengzhou 450002,china 4. State Key Laboratory of earthquake Dynamics,Institute of Geology,china earthquake administration,Beijing 100029,china Seismological Bureau of Fujian province Fuzhou 350003 China Institute of Geology China Earthquake Administration Beijing 100029 China Research Center for Exploration Geophysics China Earthquake Administration Zhengzhou 450002 China State Key Laboratory of earthquake Dynamics Institute of Geology China Earthquake Administration Beijing 100029 China

The Fuzhou basin and its vicinities are located at the northern end of the southeastern coastal seismic zone of the mainland of china. By the joint explorations of high-resolution seismic refraction and wide-angle reflection/refraction as well as deep seismic reflection in the region, which is the first synthetic profile in china, its fine velocity structure and geometric structure from the ground to Moho discontinuity is obtained. The result shows that the crust is obviously layered with a thickness of about 32 km. Basically, it consists of two parts: upper crust and lower crust. The velocity of the upper crust is 5.9-6.2 km/s in which there is a 3-4-km-thick weak low-velocity layer between the depths of 10-15 km, while the velocity of the lower crust in the range of 6.3-7.2 km/s. There exists a strong velocity gradient layer about 3 km thick above the Moho discontinuity whose velocity increases from 6.5 to 7.27 km/s. There exist high-angle normal faults that are small in size and extend only in the shallow crust. These faults are the secondary developed on the hanging wall of westward dipping low-angle normal faults. Thus, their seismogenic ability is limited, however, there exists a high-angle deep fault in the crust from Changle-Zaoan fault zone to seashore fault zone. This deep fault has cut the interface between the upper and lower crusts and Moho discontinuity, and may be the deep structure to trigger destructive earthquake source in future to affect Fuzhou City. These results have advanced the detecting precision of the deep structure in the southeastern coastal seismic zone of the mainland of china. In the aspect of the combined feature of the deep and shallow extensional structures that consist of the westward dipping low-angle normal faults and secondary normal faults on their hanging walls in the upper crust, it is firstly obtained that a united structural interpretation has deepened the knowledge about the deep dynamic process in the southeastern coasta

关键词： deep seismic reflection high-resolution seismic refraction wide-angle.

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Upper crust structure of eastern A’nyemaqên suture zone: Results of Barkam-Luqu-Gulang deep seismic sounding profile

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Acta Seismologica Sinica(English Edition) 2007年第6期20卷 628-640页

作者：张先康Geophysical Exploration Center china earthquake administration 杨卓欣Geophysical Exploration Center china earthquake administration 徐朝繁Geophysical Exploration Center china earthquake administration 潘纪顺Geophysical Exploration Center china earthquake administration 刘志Geophysical Exploration Center china earthquake administration 王夫运Geophysical Exploration Center china earthquake administration 嘉世旭Geophysical Exploration Center china earthquake administration 赵金仁Geophysical Exploration Center china earthquake administration 张成科Geophysical Exploration Center china earthquake administration 孙国伟 Geophysical Exploration Center China Earthquake Administration

Barkam-Luqu-Gulang deep seismic sounding profile runs from north of Sichuan province to south of Gansu province. It is located at the northeastern edge of Tibetan Plateau and crosses eastern A＇nyemaqên suture zone. The upper crust structures around eastern A＇nyemaqên suture zone and its adjacent area are reconstructed based on the arrival times of refracted Pg and Sg waves by using finite difference method, ray tracing inversion, time-term method and travel-time curve analysis. The results show that the depth variation of basement along profile is very strong as indicated by Pg and Sg waves. The basement rose in Zoigê basin and depressed in eastern A＇nyemaqên suture zone, and it gradually rose again northward and then depressed. The results also indicate that eastern A＇nyemaqên suture zone behaves as inhomogeneous low velocity structures in the upper crust and is inclined to- ward the south. Hoh Sai Hu-Maqên fault, Wudu-Diebu fault and Zhouqu-Liangdang fault are characterized by low velocity distributions with various scales. The distinct variation in basement depth occurred near Hoh Sai Hu-Maqên fault and Zhouqu-Liangdang fault, which are main tectonic boundaries of A＇nyemaqên suture zone. Wudu-Diebu fault, located at the depth variation zone of the basement, possibly has the same deep tectonic background with Zhouqu-Liangdang fault. The strongly depressed basement characterized by low velocity distribution and lateral inhomogeneity in A＇nyemaqên suture zone implies crushed zone features under pinching action.

关键词： eastern A'nyemaqên suture zone deep seismic refraction upper crust structures

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Distribution and identification of the low-velocity layer in the northern South china Sea

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Progress in Natural Science:Materials International 2007年第5期17卷 591-600页

作者： Zhao Minghui, Qiu Xuelin, Xu Huilong, Shi Xiaobin, Wu Shimin , Ye Chunming and Xia Shaohong (Key Laboratory of Marginal Sea Geology, South china Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, china earthquake administration of Guangdong province, Guangzhou 510070, china) [a]Key Laboratory of Marginal Sea Geology South China Sea Institute of Oceanology Chinese Academy of Sciences Guangzhou China [b]earthquake administration of Guangdong province Guangzhou China

The low-velocity layer (LVL), closely related with tectonic activities and dynamic settings, has always been a hot topic in the deep crustal structure studies. The deep seismic (OBS/OBH) and onshore-offshore experiments have been extensively implemented in the northern South china Sea (SCS) since the 1990s. Six seismic profiles were finished on the northern margin of SCS by domestic and international cooperations. The features of crustal structures were revealed and five velocity-inversion layers were discovered. Among them three LVLs with 3.0—3. 5 km·s-1 velocity are located in the sedimentary structure (2.0—6.0 km in depth and 2.0—4. 6 km in thickness) of the Yinggehai Basin and Pearl River Mouth Basin. They were identified by the reflective and refractive phases for their shallow depth. The other two LVLs with 5.5—6.0 km·s-1 velocity generally existed in the middle crust (7.0—18.0 km in depth) with an about 2.5—6.0 km thickness in the transitional crustal structure of the northeastern and northwestern SCS. They were detected by the refractive phase from their overlain and underlying layers. We explored the possible tectonic formation mechanisms combining with previously reported results, which provided evidence for the formation and evolution of SCS.

关键词： low-velocity layer deep crustal structure the northern South china Sea OBS/OBH and onshore-offshore seismic experiments.

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DEFORMATION RATE CHANGES OF TECTONIC BELTS ALONG BOUNDARIES OF YUNNAN SICHAUN BLOCK AND RELATION TO GROUPED STRONG earthquakeS

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大地测量与地球动力学 2003年第B12期23卷 101-107页

作者： Cheng Wanzheng and Yang Yongling (earthquake administration of Sichuan province, Chengdu 610041, china) earthquake administration of Sichuan province Chengdu 610041 China

Deformation measurements such as short range leveling, short baseline, continuous cross fault strain measurement are carried out at different intervals from 1982 to *** these measurement sites are built across the boundary tectonic belts of Yunnan Sichuan block. On the basis of these deformation data, the annual deformation rates at all sites are calculated and their change curves with time are plotted respectively. With these calculated results, we analyze the vertical and horizontal movements of tectonic belts of Yunnan Sichuan block, and the relationship to grouped strong earthquakes occurred in the block are discussed as well. These results show that the tectonic activities in the western and southeastern Yunnan are intensive. Along some eastern boundary belts: from Qujiang, Xiaojiang fault belts in the south of Yunnan to Xianshuihe fault belts in northwestern Sichuan, present annual rate of horizontal deformation *** Xianshuihe, Xiaojiang and Longmenshan fault belts the rates of vertical deformation change are small,but the vertical deformation change rates along Anninghe and Zemuhe fault belts are comparatively large. The comprehensive analysis shows that grouped strong earthquakes will occur probably when the deformation rate changes sharply. Thus we think that sharp changes of deformation rates may be one of the seismic precursors.

关键词：地震前兆变形率地表变形云南-四川板块边缘数据计算边缘区域的横向变形纵向变形聚集的强震

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Average slip rate, earthquake rupturing segmentation and recurrence behavior on the Litang fault zone, western Sichuan province, china

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Science china Earth Sciences 2005年第8期48卷 1183-1196页

作者： XU Xiwei1, WEN Xueze2, YU Guihua1, ZHENG Rongzhang1, LUO Haiyuan2 & ZHENG Bin2 1. Institute of Geology, china earthquake administration, Beijing 100029, china 2. earthquake administration of Sichuan province, Chengdu 610041, china 1. Institute of Geology China Earthquake Administration 100029 Beijing China 2. earthquake administration of Sichuan province 610041 Chengdu China

The Litang fault zone (LFZ) is an active fault zone within the northwestern Sichuan sub-block. Field investigation reveals new evidence for its late Quaternary offset, neoteric earthquake ruptures and surface-rupturing segmentation, from which long-term slip-rates, char-acteristic earthquake magnitudes and recurrence intervals on the fault zone are estimated. This study shows that the LFZ consists of three subordinate faults, and they are the northern Maoyaba fault, Litang fault and Kangga-Dewu fault, respectively. All of them are dominated by left-lateral strike-slip with reverse dip-slip component on different segments. Based on offset landforms and ages of relevant deposits collected from seven sites, it is estimated that the average left-lateral slip-rate on the LFZ reaches 4.0±1.0 mm/a in the past 14 ka BP, and vertical (reverse) dip-slip rate in the range of 0.1―1.8 mm/a. Three subordinate faults are independent earthquake rup-turing segments, on which the maximum moment magnitude of the characteristic earthquakes is estimated to be 7.0―7.3, and their average recurrence interval to be 500―1000 a. The latest earthquake ruptures occurred 119±2 years ago on the northern Maoyaba fault, about 1890 AD on the Litang fault, and in 1948 AD on the Kangga-Dewu fault, and this may indicate a unidirectional migration for surface rupturing earthquakes along the Litang fault zone, related to stress trigger-ing between the segments.

关键词： Litang fault zone, slip rate, earthquake rupturing segmentation, recurrence interval.

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The April 14th, 2010 Yushu earthquake, a devastating earthquake with foreshocks

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Science china Earth Sciences 2010年第6期53卷 791-793页

作者： NI SiDao1, WANG WeiTao2 & LI Li3 1 School of Earth and Space Sciences, University of Science and Technology of china, Hefei 230026, china 2 Institute of Geophysics, china earthquake administration, Beijing 100081, china 3 National earthquake Infrastructure Service, china earthquake administration, Beijing 100036, china 1. School of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China2. Institute of Geophysics China Earthquake Administration Beijing 100081 China3. National Earthquake Infrastructure Service China Earthquake Administration Beijing 100036 China

In the early morning of April 14th, 2010, a strong earth- quake (Ms7.1, http://***; Mw6.9, http://neic. ***) occurred in Yushu district, Qinghai province, china. More than 2000 lives were lost and over 100000 injured,

关键词： Figure Yushu earthquake a devastating earthquake with foreshocks The April 14th 2010 very than

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