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Dynamic mechanisms of the post-seismic deformation following large events:Case study of the 1999 Chi-Chi earthquake in Taiwan of china

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Science china Earth Sciences 2009年第11期52卷 1813-1824页

作者： ZHU ShouBiao1,2 & CAI YongEn2 1 institute of Crustal Dynamics, china earthquake administration, beijing 100085, china 2 Department of geophysics, Peking University, beijing 100871, china institute of Crustal Dynamics China Earthquake Administration Beijing China Department of geophysics Peking University Beijing China

The mechanism of postseismic deformation related to strong earthquakes is important in geodynamics, and presumably afterslip or viscoelastic relaxation is responsible for the postsesimic deformation. The 1999 Chi-Chi, Taiwan of china, earthquake occurred in the region where GPS observation station is most densely deployed in the world. The unprecedented GPS data provides a unique opportunity to study the physical processes of postseismic deformation. Here we assume that the interactions of viscoelastic relaxation, afterslip, fault zone collapse, poroelastic rebound, flow of underground fluids, and all these combined contribute to the surface displacements following the main shock. In order to know the essence of the postseismic deformation after the strong event, fault zone collapse, poroelastic rebound, flow of underground fluids, and so on, are represented equivalently by the variations of the focal medium properties. Therefore, the viscoelastic relaxation, afterslip, and the variations of the equivalent focal medium properties are inverted by applying the GPS temporal series measurement data with viscoelastic finite element method. Both the afterslip rate distribution along the fault and the afterslip evolution with time are obtained by means of inversion. Also, the preliminary result suggests that viscosities of the lower crust and the upper mantle in Taiwan region is 2.7×1018 and 4.2×1020 Pa·s, respectively. Moreover, the inversion results indicate that the afterslip contributing to postseismic deformation of 44.6% in 450 days after the Chi-Chi earthquake, with 34.7% caused by the viscous relaxation and 20.7% by other factors such as fault zone collapse, poroelastic rebound, and the flow of liquids.

关键词： mechanism of postseismic deformation viscoelastic finite element method GPS temporal series data Chi-Chi earthquake

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 institute of Geodesy and geophysics Chinese Academy of Sciences Wuhan China institute of geophysics Chinese Earthquake Administration Beijing China institute of earthquake Science Chinese Earthquake Administration Beijing China earthquake administration of Jiangxi Province Nanchang China School of Earth and Space Science University of Science and Technology of China Hefei China earthquake administration of Jiangsu Province Nanjing 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.

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 institute of geophysics China Earthquake Administration Beijing China earthquake administration of Sichuan Province Chengdu 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

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 institute of Geology China Earthquake Administration Beijing China institute of earthquake Science China Earthquake Administration Beijing 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.

Locating seismic scatterers at the base of the mantle beneath eastern Tibet with PKIKP precursors

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Chinese Science Bulletin 2010年第24期55卷 723-729页

作者： SHEN XuZhang 1,2,3 & ZHOU HuiLan 1 1 Laboratory of Computational Geodynamics,Graduate University of the Chinese Academy of Sciences,beijing 100049,china 2 Lanzhou institute of Seismology,china earthquake administration,Lanzhou 730000,china 3 Lanzhou Base of institute of earthquake Prediction,china earthquake administration,Lanzhou 730000,china Laboratory of Computational Geodynamics Graduate University of the Chinese Academy of Sciences Beijing China Lanzhou institute of Seismology China Earthquake Administration Lanzhou China Lanzhou Base of institute of earthquake Prediction China Earthquake Administration Lanzhou China

Clear PKIKP precursors were observed from the Lanzhou CTBTO seismic *** measured their incident angles,arriving azimuths and differential travel times with respect to the PKIKP arrivals using array analysis *** measurements allowed us to locate the scatterers that generated the observed *** found that the scatterers are located in the lowermost mantle beneath eastern Tibet,which is featured by a high-velocity anomaly based on previous tomographic *** high velocity anomaly was interpreted as the slab remnants of the ancient Tethys *** thus speculate that the observed scatterers are either related or induced by the subducted slab.

关键词：地震前兆西藏东部下地幔散射定位地震台阵入射角度旅行时间

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 Lanzhou institute of Seismology China Earthquake Administration Lanzhou China Lanzhou Base of earthquake Science institute China Earthquake Administration Lanzhou 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

Relationship between the Asian-Pacific oscillation and the tropical cyclone frequency in the western North Pacific

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Science china Earth Sciences 2008年第3期51卷 380-385页

作者： ZHOU BoTao1, CUI Xuan2 & ZHAO Ping3 1 Laboratory for Climate Studies, National Climate Center, china Meteorological administration, beijing 100081, china 2 National Meteorological Center, china Meteorological administration, beijing 100081, china 3 Chinese Academy of Meteorological Sciences, china Meteorological administration, beijing 100081, china Laboratory for Climate Studies National Climate Center China Meteorological Administration Beijing China National Meteorological Center China Meteorological Administration Beijing China Chinese Academy of Meteorological Sciences China Meteorological Administration Beijing China

The relationship between the Asian-Pacific oscillation (APO) and the tropical cyclone frequency over the western North Pacific (WNP) in summer is preliminarily investigated through an analysis of ob- served data. The result has shown clearly that APO is significantly and positively correlated to the tropical cyclone frequency in the WNP. If APO is above (below) the normal in summer, more (less) tropical cyclones will tend to appear in the WNP. The present study also addresses the large-scale at- mospheric general circulation changes underlying the linkage between APO and the WNP tropical cy- clone frequency. It follows that a positive phase of summer APO is concurrent with weakened as well as northward and eastward located western Pacific subtropical high (WPSH), low-level convergence and high-level divergence, and reduced vertical zonal wind shear in the WNP, providing favorable envi- ronment for the tropical cyclone genesis, and thus more tropical cyclones will come into being, and vice versa.

关键词： Asian-Pacific oscillation western North Pacific tropical cyclone atmospheric circulation

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.

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