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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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A circum-earth shear zone at low-latitudes and episodic large earthquakes in it and the circum-Pacific seismic zone

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science china Earth sciences 2006年第9期49卷 897-903页

作者： MA Zongjin1, DU Pinren1, REN Jinwei2 & GAO Xianglin1 1. institute of Geology, china earthquake administration, beijing 100029, china 2. institute of earthquake science, china earthquake administration, beijing 100036, china 1. institute of Geology China Earthquake Administration Beijing 100029 China 2. institute of earthquake science China Earthquake Administration Beijing 100036 China

Because of the differential motions between the Northern and Southern Hemispheres of the Earth, there exists a motion discordant zone between them. On the surface this zone consists of 13 large faults dominant with strike-slip. We call it a global shear zone at low-latitudes (E system). By statistical analysis of temporal distribution of earthquakes Mw≥7.5 in the E system and the circum-Pacific (P system) during 1900―2003, we find that there exist quasi-episodic and alternative activities in and between these two systems. This phenomenon is likely associated with the half-sphere oscillation in dilation and contraction and the change of the Earth’s rotation rate.

关键词： shear zone, circum-Pacific zone, great earthquake, quasi-episode.

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Two types of changes in apparent resistivity in earthquake prediction

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science china Earth sciences 2011年第1期54卷 145-156页

作者： DU XueBin1,2 1Lanzhou institute of Seismology, china earthquake administration, Lanzhou 730000, china 2Lanzhou Base of earthquake science institute, china earthquake administration, Lanzhou 730000, china 1. Lanzhou institute of Seismology China Earthquake Administration Lanzhou 730000 China2. Lanzhou Base of Earthquake Science Institute China Earthquake Administration Lanzhou 730000 China

Two types of changes in apparent resistivity (AR) have been linked to earthquake occurrences. This paper studies the changes and their causes, in detail with the ultimate purpose of developing and assessing a method of earthquake (EQ) prediction. The AR changes of the first type (CFT) are considered to be precursors related to earthquakes (EQs); these appear mostly in the medium-term period before EQs and in the short-term period preceding EQs. The changes of the second type (CST) are characterized by a turning anomaly of a long-trend AR variation or the drastically descending/ascending anomaly superimposed on such a variation; these appear synchronously in large areas, such as the chinese mainland, and northern and northwestern china, ect. Their spatio-temporal clusters correspond well to high seismicities in the areas and distant great EQs around the chinese mainland. Based on the behaviors of the two types of changes, the AR changes observed prior to the Ms8.0 Wenchuan EQ of 2008 are studied. The results show that in the medium-term period before the EQ, noticeable anomalies appeared synchronously at four stations around the Songpan-Ganzi active block, but only weak upward changes were observed in the short-term period preceding the EQ, which caused the prediction of the imminent EQ to fail.

关键词： strong earthquake apparent resistivity two types of changes spatio-temporal cluster Wenchuan earthquake

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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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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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High-resolution Rayleigh wave phase velocity maps from ambient noise tomography in North china

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earthquake science 2012年第3期25卷 241-251页

作者： Jiatie Pan institute of Geophysics, china earthquake administration, beijing 100081, china 1. institute of Geophysics China Earthquake Administration Beijing 100081 China

We presented high-resolution Rayleigh wave phase velocity maps at periods ranging from 5 s to 30 s in the northeast part of the North china Craton (NNCC). Continuous time-series of vertical component between October 2006 and December 2008, recorded by 187 broadband stations temporarily deployed in the NNCC region, have been cross-correlated to obtain estimated fundamental mode Rayleigh wave Green’s functions. Using the frequency and time analysis technique based on continuous wavelet transformation, we measured 3 667 Rayleigh wave phase velocity dispersion curves. High-resolution phase velocity maps at periods of 5, 10, 20 and 30 s were reconstructed with grid size 0.25°× 0.25°, which reveal lateral heterogeneity of shear wave structure in the crust and upper mantle of NNCC. For periods shorter than 10 s, the phase velocity variations are well correlated with the principal geological units in the NNCC, with low-speed anomalies corresponding to the major sedimentary basins and high-speed anomalies coinciding with the main mountain ranges. Within the period range from 20 s to 30 s, high phase velocity observed in eastern NCC is coincident with the thin crust, whereas low phase velocities imaged in central NCC is correlated to the thick crust. However, the low-velocity anomaly in the beijing-Tianjin-Tangshan region displayed in the 20 s and 30 s phase maps may be associated with fluids.

关键词： Rayleigh wave phase velocity ambient noise tomography wavelet transformation North china Craton

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An experimental study on variation of thermal fields during the deformation of a compressive en echelon fault set

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Progress in Natural science:Materials International 2007年第3期17卷 298-304页

作者： LIU Peixun, MA Jin, LIU Liqiang, MA Shengli and CHEN Guoqiang (Laboratory of earthquake Dynamics, institute of Geology, china earthquake administration, beijing 100029, china) [a]Laboratory of earthquake Dynamics Institute of Geology China Earthquake Administration Beijing China

The temperature variations during deformation of a compressive en echelon fault set in a rock sample were measured by a surface measurement system with multi-point platinum resistance thermometers and an infrared thermal image system. The measurements obtained by the two systems were in agreement with each other, indicating a relationship between temporal-spatial variations of the thermal field and changes of stress and strain. At varied structural positions of the rock sample, the rising of the temperature was different, implying distinct stress distributions at these positions. In the experiment, the deformation process of the sample included three stages: elastic deformation, stick-slip, and rupture. Correspondingly, the variation process of temperature had also three stages, each of which had its own temperature rising profile. And the thermal radiation field showed a similar process. These phenomena mean that the dominant mechanisms of temperature rising in all stages of deformation are different. Experimental results provide a physical basis for the study of current fault activities by using data of satellite infrared images.

关键词： en echelon fault set stick-slip thermal infrared radiation temperature mechanism of temperatnre rising.

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A preliminary study on seismic design criteria of offshore platforms in Bohai Sea of china

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earthquake Engineering and Engineering Vibration 2010年第2期9卷 223-231页

作者： Peng Yanju1,Lu Yuejun1,Yan Jiaquan2,Tang Rongyu1,Wang Junqin3 and Li Jiagang3 1. institute of Crustal Dynamics,china earthquake administration,beijing 100085,china 2. institute of Geophysics,china earthquake administration,beijing 100081,china 3. beijing Research Center of china National Offshore Oil Corp.,beijing 100027,china institute of Crustal Dynamics China Earthquake Administration Beijing 100085 China

This paper analyzes the seismicity in Bohai Sea,introducing a shape factor K to characterize the seismic risk distribution in sub-regions of the sea. Based on the seismic design ground motions for 46 platforms located in the Bohai Sea,a statistical analysis was performed for different peak ground acceleration (PGA) ratios at two different probability levels. In accordance with the two-stage design method,a scheme of two seismic design levels is proposed,and two seismic design objectives are established respectively for the strength level earthquake and the ductility level earthquake. By analogy with and comparison to the chinese seismic design code for buildings,it is proposed that the probability level for the strength level earthquake and ductility level earthquake have a return period of 200 and 1000 - 2500 years,respectively. The validity of these proposed values is discussed. Finally,the PGAs corresponding to these two probability levels are calculated for different sub-regions of the Bohai Sea.

关键词： fixed offshore platform seismic design level seismic design objective return period Bohai Sea

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Revision of seismic design codes corresponding to building damagesin the “5.12” Wenchuan earthquake

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earthquake Engineering and Engineering Vibration 2010年第2期9卷 147-155页

作者： Wang Yayong institute of earthquake Engineering, china Academy of Building Research, beijing 100013, china institute of earthquake Engineering China Academy of Building Research Beijing 100013 China

A large number of buildings were seriously damaged or collapsed in the "5.12" Wenchuan earthquake. Based on field surveys and studies of damage to different types of buildings, seismic design codes have been updated. This paper briefly summarizes some of the major revisions that have been incorporated into the "Standard for classification of seismic protection of building constructions GB50223-2008" and "Code for Seismic Design of Buildings GB50011-2001." The definition of seismic fortification class for buildings has been revisited, and as a result, the seismic classifications for schools, hospitals and other buildings that hold large populations such as evacuation shelters and information centers have been upgraded in the GB50223-2008 Code. The main aspects of the revised GB50011-2001 code include: (a) modification of the seismic intensity specified for the Provinces of Sichuan, Shanxi and Gansu; (b) basic conceptual design for retaining walls and building foundations in mountainous areas; (c) regularity of building configuration; (d) integration of masonry structures and precast RC floors; (e) requirements for calculating and detailing stair shafts; and (f) limiting the use of single-bay RC frame structures. Some significant examples of damage in the epicenter areas are provided as a reference in the discussion on the consequences of collapse, the importance of duplicate structural systems, and the integration of RC and masonry structures.

关键词： Wenchuan earthquake earthquake damage to buildings revision of seismic design codes

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