Table of Content

30 September 2013, Volume 35 Issue 3

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CONTENTS

FEATURES OF SEISMOGENIC PROCESS OF THE LONGMENSHAN FAULT ZONE DERIVED FROM ANALYSIS ON THE TEMPORAL-SPATIAL EVOLUTION OF EARTHQUAKES

MA Jin, LIU Pei-xun, LIU Yuan-zheng

2013, 35(3):  461-471.  DOI: 10.3969/j.issn.0253-4967.2013.03.001

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Within almost five years,the 2008 Wenchuan M_S 8.0 and 2013 Lushan M_S 7.0 earthquakes ruptured the Longmenshan Fault zone successively. The characteristics of earthquakes and their development tendency on this fault zone have been a focus of subject of research. This article attempts to explore some features of seismic preparation process of the 2008 Wenchuan event from temporal-spatial evolution of earthquakes along the Longmenshan Fault zone during more than 40 years.(1)The spatial range of the earthquake preparation,or seismic nucleation,is much smaller than that of co-seismic rupturing. It indicates that the seismic source,probably consisting of some small asperities or barriers,prepared on a finite fault segment can be connected and expand into a large-scale rupture section along the fault when the fast instability occurs at the source.(2)Prior to the 2008 Wenchuan giant shock,its preparation area had experienced a dense distribution of small earthquakes for eight years or more,while no conspicuous slip and deformation were observed on the surface. This implies that the seismogenic fault segment of the Wenchuan event on the Longmenshan Fault was undergoing probably compressive deformation,accompanied with cataclastic process. When the cataclastic deformation of the great-shock source reached a critical state,fault instability occurred along the fault with rapid rupturing. (3)To further study the variations of the main-shock area prior to the event,this article analyzes the temporal-spatial processes of small earthquakes around the main shock since 2004 recorded by a special seismic network in the Zipingpu reservoir. The results indicate that the scope of the seismicity expanding along the fault took place along the fault in October 2005 and October 2006,respectively,in accordance with the time when the reservoir reached its high water level. Among them,the second expanding from October 2006 covered a relatively large area and with relatively big magnitudes,implying great importance for the study of the final instability process of the 2008 Wenchuan huge earthquake. Besides,this paper discusses the correlation of the rupturing process of the 2008 Wenchuan giant event with the geometry of the fault and the reason why the 2013 Lushan earthquake occurred many years after the Wenchuan event rather than immediately following this giant shock like usual big aftershocks. The research results are helpful for understanding of seismogenic processes of major earthquakes of the thrust type.

THE STUDY OF THE LEFT-LATERAL DISPLACEMENT ON THE XIANGSHAN-TIANJINGSHAN FAULT IN LATE QUATERNARY

YIN Gong-ming, JIANG Ya-feng, YU Gang, HAN Fei, LIU Chun-ru

2013, 35(3):  472-479.  DOI: 10.3969/j.issn.0253-4967.2013.03.002

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Xiangshan-Tianjingshan Fault is one of the major active faults of the arc fault zone on the northeastern margin of the Qinghai-Tibet Plateau. The Yellow River in the Shapotou area flows through the fault and forms a perfect "Ω-shape" bend. Shapotou not only is a tourist mecca,but also a hotspot for studying the geomorphology,neotectonics,the uplift of Qinghai-Tibet Plateau and other issues. Xiangshan-Tianjingshan Fault is mainly a left-lateral strike-slip fault with a minor thrust component. So to study the fault's offsets is of vital importance. This paper,based on the characteristic of the distribution of the Yellow River terraces in the Shapotou Big Bend area,analyzes the offsets of the Xiangshan-Tianjingshan Fault since the formation of the terraces. The results reveal that 3 river terraces are developed on the right of the Yellow River in the Shapotou area,while there is no terrace developed on the left of the river. The maximum left-lateral displacement of Xiangshan-Tianjingshan Fault is less than 880m,and the slip rate is less than 5.18mm/a since 170ka BP.

TECHNOLOGY AND SEVERAL CASES FOR INTER-MEDIATE-AND LONG-TERM PREDICTION OF THE MAGNITUDE 6～7 EARTHQUAKE

CHEN Li-chun, RAN Yong-kang, WANG Hu, LI Yan-bao, MA Xing-quan

2013, 35(3):  480-489.  DOI: 10.3969/j.issn.0253-4967.2013.03.003

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In general,the displacement produced by a magnitude 6～7 earthquake is relatively small,even does not reach the surface,so it is difficult to be preserved in geological records. On the other hand,the seismogenic fault of such earthquakes is easy to be considered incorrectly as a non-active fault since Holocene,consequently overlooking the real seismic hazard in the future. To solve this problem,we propose a type of faults that are capable of generating M6～7 earthquakes,but with weak surface activity and cannot produce conspicuous surface displacement. To recognize such faults from geological records,which have no visible evidence of activity since middle-late Pleistocene,is the key to intermediate-and long-term earthquake prediction. The specific procedures of the technology are as follows: First,we determine the seismotectonic setting of the tectonic system in which the target fault lies. Second,we establish the relation between the target fault and other active faults in the same tectonic system,which have records of historical earthquakes or paleoearthquakes. Then we compare varied seismogenic units in the same-order structure,same tectonic system,and varied stages in the same tectonic process. The case studies demonstrate that this is an effective method for intermediate-and long-term earthquake prediction. The cases studied include the Puduhe-Xishan Fault in Kunming City,Hanzhong Basin in the north section of the Longmen Shan Fault zone,Dachuan-Shuangshi Fault in the south section of the Longmen Shan Fault zone,and the Guguan-Guoshun Fault of the Longxian-Baoji Fault zone. These faults all show weak activities on the surface and have potential for earthquakes with estimated magnitude 6.5～7.0.In addition,by estimation using this method,the Taoyuan-Guichuan Fault of the Longxian-Baoji Fault zone has a seismic risk of M6.0～6.5 earthquake,and the Longxian-Qima-Mazhao Fault is capable of producing an earthquake about M7.5.

DEEP STRUCTURE AND QUATERNARY ACTIVITIES OF THE XIADIAN FAULT ZONE

HE Fu-bing, BAI Ling-yan, WANG Ji-ming, LIU Yu, CAI Xiang-min, SUN Yong-hua, ZHANG Lei, FANG Tong-ming, GUO Gao-xuan

2013, 35(3):  490-505.  DOI: 10.3969/j.issn.0253-4967.2013.03.004

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Xiadian Fault zone is a NNE-trending lithospheric-scale regional deep fault in the eastern part of the capital,also an active fault zone with strong earthquake activities in the history. According to the results of gravity,shallow seismic and high-density electrical geophysical prospecting,by "relay stitching" vertically from the deep to the shallow,and in combination with the methods of drilling and other means,the Xiadian Fault zone is studied by dividing it into two parts: the bedrock fault zone and the Quaternary fault zone,and new insights are gained on the characteristics of deep structure and activity of the Xiadian Fault zone. The results show that: (1)the bedrock fault zone of Xiadian Fault consists of main faults and secondary faults. Its northern part,the Mafang-Xiji area,is composed of two major faults with a narrower width,and the southern part,the Xiji-Fengheying area,is composed of three major faults,with a wider width; (2)The Quaternary fault zone of Xiadian Fault is the upward extension of the bedrock fault zone,which is the visual representation of the latest activity of the fault zone and controlled by the bedrock fault zone. The Quaternary fault zone is also composed of main faults and secondary faults. The northern part(Mafang-Xiji area)consists of two major faults and secondary faults distributed in the northern end,corresponding well with the bedrock fault zone. Occurrence of the two major faults is quite different,and the latest movement of the faults is both in Holocene. While,the southern part of the fault zone(the Xiji-Fengheying area)is quite discontinuous and is difficult to distinguish between the major and secondary faults. The faults have poor correspondence to the bedrock ones and are inferred to be related with the segmentation of faulting of the bedrock faults. Both major and secondary faults are steep and the date of their latest movement is late Pleistocene-early Holocene; (3)The amount of vertical dislocation of the bottom boundary of the Holocene sediments in the hanging and foot walls of Xiadian Fault zone is 1.7～4.8m,and that of late,middle and early Pleistocene are 6～26m,26～167m and 44～330m,respectively. The vertical dislocation on the whole fault zone differs greatly,with the highest in the Xiadian area,and decreasing gradually to the south and north ends; (4)Considering the spatial distribution,structure,occurrence,activity and characteristics of seismic activity along of the fault zone,the Xiadian Fault zone is divided into the southern and northern segments with the Zhangjiawan Fault as the boundary. The northern part experienced intensive Quaternary activity,with frequent moderate and small earthquakes. Quaternary activity is weak along the southern part,where only small earthquakes occurred.

CENOZOIC FAULT ACTIVITY OF THE SOUTHERN SEGMENT OF THE LONGMENSHAN THRUST BELT：EVIDENCE FROM LOW-TEMPERATURE THERMOCHRONOLOGY DATA

TAN Xi-bin, LEE Yuan-hsi, XU Xi-wei, CHEN Wen-yu, XU Chong, YU Gui-hua

2013, 35(3):  506-517.  DOI: 10.3969/j.issn.0253-4967.2013.03.005

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The Longmen Shan,located at the eastern margin of the Tibetan plateau,is a steep and high exhumation area. In recent years,the 2008 Wenchuan M_W7.9 earthquake and the 2013 Lushan M_S7.0 earthquake occurred,and researchers presented a lot of low-temperature thermochronology data of the Longmen Shan and adjacent area. In this paper,we provide 4 ZFT ages and 4 AFT ages for the southern segment of the Longmenshan Thrust Belt(LTB),where the low-temperature thermochronology data are still few. Combining with previous researches,we get the Cenozoic exhumation history of the Baoxing Massif,located at the southern segment of the LTB,and new knowledge about the Cenozoic activity of the southern segment of the LTB.The Baoxing Massif began quickly cooling in the early Cenozoic,with the cooling range exceeding 225℃,while the cooling range of the Pengguan Massif in the central segment of the Longmen Shan is between 185～225℃.The four AFT ages in the Baoxing Massif are between 2.7～5.0Ma,which are younger than that in the Pengguan Massif,and it indicates that the late-Cenozoic cooling rate of the Baoxing Massif is bigger than that of the Pengguan Massif. Under this assumption that the surface temperature is 15℃ and the paleo-geothermal gradient is 30℃/km,the average exhumation rate from 3～5Ma to present is about 0.63～1.17mm/yr. The low-temperature thermochronology data indicate that the differential exhumation is concentrated in the Beichuan-Yingxiu Fault and the Jiangyou-Guanxian Fault in the central segment of the LTB,while it is dispersed in a wider region along the two branches of the Shuangshi-Dachuan Fault and the faults and folds to the east,in the southern segment.

SEISMIC HAZARD ANALYSIS OF THE MAIN FAULTS IN CHONGQING URBAN AREA

LI Feng, ZHANG Xiao-liang, LIU Hua-guo

2013, 35(3):  518-531.  DOI: 10.3969/j.issn.0253-4967.2013.03.006

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The maximum magnitude of probable future earthquake in the target area is forecasted in this paper by synthetical analysis of tectonic structure,seismicity,stress and strain fields,based on data of the Chongqing urban active faults surveying. The maximum magnitude of probable future earthquake in the target area is 5.5≤M_S≤6.0. We try to use the spatially smoothed seismicity method in weakly active area. Two seismic hazard models in weakly active area based on spatially smoothed seismicity method are proposed using strong seismic catalog and small seismic catalog. The completeness of these two catalogs is analyzed based on EMR(Entire Magnitude Range)method. And the seismic hazard(probability)in the target area is calculated using Poisson model. The results show that the seismic probability value for a single fault is relatively low and the possibility of destructive earthquake of magnitude above 5.5 in the target area is small. There are still some uncertainty and reliability for the results because of the hypnosis of the spatially smoothed seismicity model. However it should be noticed that the technique of seismic hazard calculation described in this paper based on spatially smoothed seismicity method is a new try and has potential application for the weakly active area such as Chongqing.

PRESENT-DAY ACTIVITY OF ASHIKULE VOLCANIC GROUP FROM INSAR

JI Ling-yun, XU Jian-dong, ZHAO Bo, WAN Yuan, SHEN Huan-huan

2013, 35(3):  532-541.  DOI: 10.3969/j.issn.0253-4967.2013.03.007

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The Ashikule volcanic group is located in the Ashikule Basin,which is situated about 250km south of Yutian County,Xinjiang. Ashikule volcanic group consists of more than 10 large volcanoes and dozens of small volcanoes. Its present-day activity is unknown due to the extremely high altitude and inclement weather. Based on Envisat ASAR and ALOS PALSAR images,we obtain the land surface deformation field(2003-2010)by using stacking InSAR(Interferometric Synthetic Aperture Radar)and SBAS-InSAR(Small BAseline Subsets-Interferometric Synthetic Aperture Radar)techniques. We also analyze the volcanic activity based on the InSAR-derived deformation field. Our results show that the deformation of Ashikule volcanic group was not obvious before the 2008 Yutian earthquake(2003-2007).However,it showed a large-scale movement towards satellite after the 2008 Yutian earthquake(2008-2010)with largest accumulated displacement of 1cm. We speculate the large-scale movement had nothing to do with volcanic activity,but it was a result of stress adjustment caused by the 2008 Yutian earthquake. Nevertheless,the northmost end of the coseismic rupture showed movement towards east,and also deflated very much with accumulated subsidence of 6cm.

A DISCUSSION ON THE TYPE OF THE QIXIANGZHAN ERUPTION OF CHANGBAISHAN TIANCHI VOLCANO, NORTHEAST CHINA

PAN Bo, FAN Qi-cheng, ZHONG Guang-pei, XU Jian-dong, WAN Yuan

2013, 35(3):  542-552.  DOI: 10.3969/j.issn.0253-4967.2013.03.008

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Changbaishan Tianchi volcano is one of the most dangerous active volcanoes in Northeast Asia. It experienced three periods of large-scale eruptions since the Holocene,i.e.the Tianwenfeng period at about 5,000 years ago,the Qixiangzhan period at about 4,000 years ago and the Millennium eruption at about 1,100 years ago,respectively. The type of Tianwenfeng and Millennium eruptions is commonly accepted to be a typical Plinian eruption. However,there arises a considerable debate about the type of Qixiangzhan eruption as whether it is effusive or explosive. In high-resolution remote-sensing images,the morphology of the products of Qixiangzhan eruption looks like a lava flow,which erupts from Qixiangzhan parasitic crater,and flows along the northern slope of the volcanic cone about 5.4km in length and 400～800m in width. However,the recent researches by the author have revealed that the Qixiangzhan eruption should be a small-scale pulsed explosive eruption. The main evidence is as follows: 1)The bulk-rock composition of Qixiangzhan eruption products is characterized by high SiO₂(≥71%)and Na₂O+K₂O(≥10%)contents representative of alkaline magma,which has high viscosity,low flowing ability and extremely high potential of explosive eruption; 2)Field observations show that the Qixinagzhan eruption products appear as thin layers about 2～5cm in thickness,the central part of which is welded stronger than the edge,significantly different from the massive or slaggy structures of lava flow. In addition,flame structures indicative of explosive eruption are well developed in the volcanic deposits around parasitic crater; 3)Microscopic observation reveals that most of the phenocrysts in the Qixiangzhan eruption products were severely broken by explosion to form angular grains with well developed micro-cracks. The vesicles in the Qixiangzhan eruption products are irregular in shape and have rough margin,different significantly from the elliptical and smooth margin vesicles commonly observed in lava flow; 4)Stereomicroscopic observation shows that the Qixiangzhan eruption products are composed of clastic particles and exhibit grain-supported texture with well developed irregular vesicles. Based on the above analyses,we may conclude that the Qixiangzhan eruption can be assigned to a small-scale pulsed explosive eruption. During the explosive eruption,a large number of fine pyroclastic particles flowed down the mountain slope as a high speed pyroclasstic flow to form thin layer of ignimbrite under the action of high temperature and strong shear forces. Over many times of explosive eruptions,layer upon layer of ignimbrite were accumulated,resulting in a shape just like lava flow. Therefore,all the three large eruptions of Changbaishan Tianchi volcano in Holocene can be assigned to explosive eruption,rather than the previously proposed model of explosive-effusive-explosive explosions.

ANALYSIS OF WATER LEVEL CHANGES AND DEFORMATION PROCESS OF THE MIDDLE AND SOUTHERN SEGMENTS OF XIAOJIANG FAULT ZONE

TANG Yan-dong, LIU Chun-ping, LIAO Xin, SHI Yun, WAN Fei

2013, 35(3):  553-564.  DOI: 10.3969/j.issn.0253-4967.2013.03.009

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This paper analyses the deformations of middle and southern segments of Xiaojiang Fault zone using the theory of phase shift and amplitude changes between tidal water level and earth tides caused by water exchange among the systems of well hole-fracture-micro fracture. Seismic waves and deformation caused by tectonic stress can lead to changes of phases shift and amplitudes of tide levels in fractured confined aquifer. Seismic waves can increase water exchange between the aquifer and the borehole. So the fluid pathways can be unclogged during the earthquake and permeability in the fractured rock system can be increased after the earthquake. Smaller phase shift lag implies the higher permeability in the system. Permeability will return to background value gradually because of reclogging of fluid pathways and phase shift decreases. The long-term trend of phase shift represents the information of aquifer deformation caused by tectonic stress. The middle and southern segments of Xiaojiang Fault zone deform differently. The middle segment of the fault zone shows both strike-slip and compression characteristics. Deformation of this section is accumulated continuously. Phase shift and amplitude of the monitoring wells located at the intersection of Xiaojiang Fault zone and Honghe Fault zone change in a small scope. This shows that deformation of this section is not obvious and the aquifer is not squeezed remarkably.

3D VISUALIZATION AND MODELING OF SPATIAL RELATIONSHIP BETWEEN EARTHQUAKES AND ACTIVE FAULTS

LI Zi-hong, LIU Hong-fu, ZHANG Min, ZENG Jin-yan

2013, 35(3):  565-575.  DOI: 10.3969/j.issn.0253-4967.2013.03.010

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Nowadays,as the information is highly advanced,the visualization in scientific computing(VISC)is developing rapidly and the three-dimensional Geographic Information System(3D GIS)also becomes one of the hot topics of GIS research. The 3D geological modeling,which is closely related to the VISC and 3D GIS,has drawn more and more attention of domestic and foreign experts and scholars; it has been highly desirable to resolve the complex geological problems in a 3D space.In view of the above research topic and combining the project of Taiyuan Active fault Survey and Seismic Risk Assessment,the 3D space database of shallow seismic survey is established based on the detailed analysis and sorting of a large amount of exploration data in this paper. The algorithm of the 3D geological model is also designed by use of ArcGIS's powerful 3D displaying function,and then the program is developed using the AOVAB.Based on the 3D geological modeling technology which combines the VISC and 3D GIS,the 3D geological visualization model is developed for the Quaternary stratigraphic sections and fault profiles within the Taiyuan active fault survey area,and the 3D buffer model is also tried to be established under the ArcGIS environment in view of the 3D fault model. The statistical analysis of active fault data and seismic data is carried out,and the relationship between active faults and spatial distribution of earthquakes is studied.This study accomplished the 3D geological model for the Quaternary stratigraphic sections,fault profiles and 3D space buffer within the Taiyuan active fault survey area,and carried out the analysis of the relationship between faults and spatial distribution of historic earthquakes based on this model. These results have significance for theoretical and scientific studies,and can provide reference to active faults survey in other cities in the future.

THE RESEARCH ON SELF-NOISE MEASUREMENT METHOD OF MOVEABLE BROADBAND SEISMOMETER

YIN Xin-zhong, CHEN Jiu-hui, LI Shun-cheng, GUO Biao

2013, 35(3):  576-583.  DOI: 10.3969/j.issn.0253-4967.2013.03.011

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This article uses two-sensor coherence analysis method(Holcomb,1989)and three-sensor coherence analysis method(Sleeman,2006)to calculate the self-noise models for CMG-3T,BBVS-120 and STS-2 seismometers. The results show that: 1)Sleeman's method can avoid the error caused by the transfer function in calculation and can extract more potentially and efficiently the background noise than the Holcomb's method does; 2)Under our simple test condition,the self-noise of the three sensors in 0.06～1Hz band is lower than NLNM,which represents a quite good noise performance; 3)In the observation process of movable seismic array,the sensor alignment and sensor insulation protective measure are important factors to guarantee a good performance of the instruments.

COMPREHENSIVE ASSESSMENT OF THE EARTHQUAKE PREVENTION AND DISASTER REDUCTION ABILITY OF CHINA

DENG Yan, SU Gui-wu, WU Huan-jie

2013, 35(3):  584-592.  DOI: 10.3969/j.issn.0253-4967.2013.03.012

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Aimed to scientifically allocate the earthquake prevention and disaster reduction resources,this paper firstly analyzes the definition of regional earthquake prevention and disaster reduction ability of China from the absolute and relative two levels: The former is a regional function to prevent from earthquake attacking and to reduce disaster losses which are determined by the region's various characteristics such as natural,economic,social and culture conditions,while the latter,based on the former,is the disaster-reduction capacities according to the earthquake disaster loss. Then,the paper constructs the evaluation index system for the absolute ability of China,which includes one object layer,three rule layers,thirteen factor layers and sixteen variable layers. Finally,the study puts forward the comprehensive assessment of absolute ability and relative ability and draws the contribution maps of them. The result shows that there are obvious regional differences of both the absolute ability and the relative ability in China. Meanwhile,there exist obvious regional differences between them. The former shows that the ability in eastern region is generally higher than the national average ability,the central and northwestern areas are equal or lower than it,and Tibetan plateau region is the lowest,which is closely related with the distribution characteristics of different regional economic development levels. While for the latter,either in terms of relative ability against the earthquake deaths or relative ability against earthquake economic loss,the low value areas are concentrated in the North China plain,north-south seismic belt,southeast coast and Northeast China plain,which is mainly determined by the matching pattern between the absolute capabilities and the future earthquake damage.

ANALYSIS ON THE CHARACTERISTICS OF THE M_S6.6 MINXIAN-ZHANGXIAN EARTHQUAKE HAZARD IN GANSU PROVINCE,CHINA ON JULY 22,2013

LI Zhi-qiang, JIANG Li-xin, LI Yi-gang, YU Shi-zhou, LU Ning, LI Meng, YUAN Zhi-xiang, FENG De-chun

2013, 35(3):  593-603.  DOI: 10.3969/j.issn.0253-4967.2013.03.013

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At 7: 45 on July 22,2013,an M_S6.6 earthquake hit Minxian County(34.5°N,104.2°E)of Dingxi City in Gansu Province,which brought 95 deaths and after which an emergency response of second grade was declared by China Earthquake Administration. In this earthquake,the intensity of the meizoseismal region is Ⅷ.Buildings in quake-hit region are mainly of civil structure and timber structure,which account for more than 90%.Unfortunately the anti-seismic ability of these two kinds of buildings is poor. To make things worse,most of them are old. And it had been rainy for days before the earthquake,which lowered the support ability of the foundation and the wall. After the earthquake,in comparison with other earthquakes,buildings of civil structure and timber structure are damaged more heavily in the region of the same intensity,and the damage of buildings of both brick structure and brick-concrete structure is obviously lighter. Significantly thick loess coverage and continuous rainfall gave birth to many landslides. For these reasons,the regions of both Ⅷ and Ⅵ intensity are relatively larger. Dingxi City,which the earthquake hit,is one of the most undeveloped regions in China,and the proportion of buildings of civil structure and timber structure,which behaved badly in the earthquake,is abnormally large. Thus it is suggested that the reconstruction aid should be expanded so that buildings can be built with the masonry-timber and brick-concrete as the main structures.

DISTRIBUTION OF THE RELATED DISASTER AND THE CAUSATIVE TECTONIC OF THE MINXIAN-ZHANXIAN M_S6.6 EARTHQUAKE ON JULY 22,2013,GANSU,CHINA

ZHENG Wen-jun, MIN Wei, HE Wen-gui, REN Zhi-kun, LIU Xing-wang, WANG Ai-guo, XU Chong, LI Feng

2013, 35(3):  604-615.  DOI: 10.3969/j.issn.0253-4967.2013.03.014

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On July 22,2013,the Minxian-Zhanxian M_S 6.6 earthquake occurred at the central-northern part of the South-North Seismic Belt. In the area,complicated structural geometries are controlled by major strike-slip fault zones,i.e.the Eastern Kunlun Fault and the Northern Frontal Fault of West Qinling. The distribution of related seismic disasters,namely,the ellipse with its major axis trending NWW,is in good accord with the strike of the Lintan-Tanchang Fault. Severe damages in the meizoseismal area of the Minxian-Zhangxian M_S 6.6 earthquake are located within the fault zone. So it is considered that the earthquake related damages are closely related to the complicated geometry of the Lintan-Tanchang Fault,and it also indicates that the earthquake is the outcome of joint action of its secondary faults. Based on field investigations,and by integrating the results of previous studies on active tectonics,structural deformation and geophysical data,it can be inferred that the southward extension of the Northern Frontal Fault of West Qinling and the northeastward extrusion of the Eastern Kunlun Fault in the process of northeastward growth of Tibetan plateau are the main source of tectonic stress. Basic tectonic model is provided for strong earthquake generation on the Lintan-Tanchang Fault.

LANDSLIDES TRIGGERED BY THE 2013 MINXIAN-ZHANGXIAN, GANSU PROVINCE M_S 6.6 EARTHQUAKE AND ITS TECTONIC ANALYSES

XU Chong, XU Xi-wei, ZHENG Wen-jun, MIN Wei, REN Zhi-kun, LI Zhi-qiang

2013, 35(3):  616-626.  DOI: 10.3969/j.issn.0253-4967.2013.03.015

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On July 22,2013,an earthquake of M_S 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.

SHAKEMAP OF PEAK GROUND ACCELERATION WITH BIAS CORRECTION FOR THE LUSHAN, SICHUAN EARTHQUAKE ON APRIL 20,2013

CHEN Kun, YU Yan-xiang, GAO Meng-tan, GAO Jing-chun

2013, 35(3):  627-633.  DOI: 10.3969/j.issn.0253-4967.2013.03.016

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After the Lushan,Sichuan earthquake on April 20,2013,based on the tectonic background,the distribution of active faults in the epicenter area,the focal mechanism solutions of this earthquake,the ground motion attenuation in western China and local site effect,ShakeMap of PGA was acquired. Then,distribution of PGA was amended by using PGA observations to correct system bias of theoretical estimates in the area without PGA observations. The results show that the vibration in epicenter area increased because the Lushan earthquake is a high-angle thrust earthquake. Especially,the vibration within 30km of the epicenter is more intense than the uncorrected results.

A PHENOMENON OF GROUND TEMPERATURE CHANGE PRIOR TO LUSHAN EARTHQUAKE OBSERVED IN KANGDING

CHEN Shun-yun, LIU Pei-xun, LIU Li-qiang, MA Jin

2013, 35(3):  634-640.  DOI: 10.3969/j.issn.0253-4967.2013.03.017

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Recently,the strong earthquakes in China mainland occurred mainly around the Bayanhar block. It is important to monitor the information of ongoing crustal activity at the key tectonic positions. We have developed a set of wireless equipment for measuring the ground temperature in field,and have established a network of measurement of the ground temperature along Xianshuihe Fault. Some changes of temperature were observed before and after the Lushan earthquake on April 20,2013.First of all,an apparent and persistent change of the ground temperature in Kangding appeared,starting from January 31,2013.This temperature variation corresponded with the occurrence of the small earthquakes around the observation station. According to the relationship between the temperature and stress,the abrupt change of ground temperature is essentially the geological stress adjustment. From the viewpoint of geological structures,both Longmengshan Fault and Xianshuihe Fault are the boundary faults of the Bayanhar block,but located at different boundaries,so,Kangding in Xianshuihe Fault is tectonically related to Lushan in Longmengshan Fault. Thus,the temperature change described above would possibly be the precursor of the Lushuan earthquake.

LANDSLIDES TRIGGERED BY THE APRIL 20,2013 LUSHAN, SICHUAN PROVINCE M_S 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

2013, 35(3):  641-660.  DOI: 10.3969/j.issn.0253-4967.2013.03.018

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On April 20,2013,a strong earthquake of M_S 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.

APPLYING THE NEWMARK’S MODEL TO THE ASSESSMENT OF EARTHQUAKE-TRIGGERED LANDSLIDES DURING THE LUSHAN EARTHQUAKE

CHEN Xiao-li, YUAN Ren-mao, YU Lu

2013, 35(3):  661-670.  DOI: 10.3969/j.issn.0253-4967.2013.03.019

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As a kind of secondary disasters caused by strong earthquakes,earthquake-triggered landslide has drawn much attention in the world because of severe hazards it causes. The 2013 Lushan,China,earthquake triggered lots of landslides and provided an opportunity to test various kinds of methods which have been used in earthquake triggered landslides assessment. Based on the high-resolution satellite images and aerial photos,we preliminarily interpret landslides in the damaged region. It is found that almost all of the landslides took place in the area with seismic intensity above Ⅶ.Spatially,the triggered landslides are controlled by the causative faults in their distribution and mainly concentrate around the epicenter. Based on the Newmark's method model,critical acceleration a_c is used to predict potential landslides. Comparing with the landslides occurrences in the study area,the result of our calculation proves that Newmark's model is effective in seismic hazards analysis. Also,the landslide affected area is estimated by several methods and the difference between them is discussed.

SEISMOGENIC STRUCTURES ASSOCIATED WITH THE 20 APRIL 2013 M_S 7.0 LUSHAN EARTHQUAKE, SICHUAN PROVINCE

LI Chuan-you, XU Xi-wei, GAN Wei-jun, WEN Xue-ze, ZHENG Wen-jun, WEI Zhan-yu, XU Chong, TAN Xi-bin, CHEN Gui-hua, LIANG Ming-jian, LI Xin-nan

2013, 35(3):  671-683.  DOI: 10.3969/j.issn.0253-4967.2013.03.020

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The April 20,2013,M_S 7.0 Lushan earthquake occurred along the southwestern part of the Longmen Shan Fault zone. Tectonics around the epicenter area is complicated and several NE-trending faults are developed. Focal mechanisms of the main shock and inversions from finite fault model suggest that the earthquake occurred on a northeast-trending,moderately dipping reverse fault,which is consistent with the strike and slip of the Longmen Shan Fault zone. NE-trending ground fissures and soil liquefaction along the fissures,heavy landslides along the Dachuan-Shuangshi and Xinkaidian Faults were observed during the field investigations. No surface ruptures were found in the field work. GPS data indicate that the fault on which this earthquake occurred is a fault east of or near the Lushan county and the earthquake also triggered slip on the fault west of the Lushan county. Field observations,GPS data,focal fault plane,focal depth,and distribution of the aftershocks suggest, that the seismogenic structure associated with the M_S 7.0 Lushan earthquake is the décollement beneath the folds of the eastern Longmen Shan. Slip along this decollement generated the earthquake,and also triggered the slip along the Dachuan-Shuangshi and Xinkaidian Faults.