SEISMOLOGY AND GEOLOGY

LEARNING AND PROGRESS THROUGH SCIENTIFIC PRACTICES:COMMEMORATING THE 90TH ANNIVERSARY OF THE TRAGIC HAIYUAN EARTHQUAKE,STRIVING TO ADVANCE OUR ABILITIES OF EARTHQUAKE PREDICTION AND SEISMIC HAZARD REDUCTION

DENG Qi-dong

2011, 33(1): 1-14. DOI: 10.3969/j.issn.0253-4967.2011.

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The great Haiyuan earthquake occurred at 20: 06: 09 on December 16,1920 in the southern Ningxia Autonomous Region.The magnitude of this earthquake is 8.5 which is listed as one of the three greatest earthquakes occurring in continental China.This devastating earthquake killed about 230,000 people according to previous reports.Recent studies show that total casualty might have reached 270,000. Study on this earthquake using modern scientific and technological methods is the first in the history of earthquake research in China that sets up the monument in China's earthquake science.Significant breakthrough took place in the 80s of last century.The earthquake surface rupture,with 200km in length and prominent left-lateral strike-slip displacement,was discovered.The first monograph on the Haiyuan earthquake was published.The innovative technology of large-scale geological mapping of active faults was developed during studies on the Haiyuan earthquake surface ruptures with the publication of the first large-scale map of the Haiyaun active fault.Quantitative studies were carried out on fine structures and geometry of the fault zone,Holocene slip rate,co-seismic displacement,paleoearthquake and recurrence interval of great earthquake,and future earthquake risk assessment.The innovative studies also include rupture propagation along strike-slip fault,evolution of pull-apart basin,determination of total offset across the strike-slip fault,transition equilibrium between strike-slip displacement along its major strand and crustal shortening at its end of the strike-slip fault,and the mechanism of deformation on the Liupanshan Mountains.On the occasion of the 90th anniversary of the tragic Haiyuan earthquake,the careful retrospect in scientific progresses achieved during past 20 years would lead to further directions in the studies of active faults and earthquake hazard reduction,so that we can console those killed by the Haiyuan earthquake and put forward our efforts toward earthquake prediction and seismic hazard reduction.

FEATURES OF FELDSPAR WEATHERING DISSOLUTION IN HOLOCENE VOLCANIC ERUPTIVE MATERIAL ON THE TIANWEN PEAK CROSS SECTION,TIANCHI, CHANGBAISHAN AND THEIR IMPLICATIONS

ZHANG Bing-liang, XU Jian-dong, SHI Lan-bin, PAN Xiao-dong

2011, 33(1): 15-25. DOI: 10.3969/j.issn.0253-4967.2011.01.002

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We use SEM and EDX to study the micro structures and chemical compositions of feldspar surface weathering dissolution in Holocene volcanic eruptive material at the Tianwen peak,Tianchi,Changbaishan.The result shows that there are varied micro structures formed by weathering dissolution on feldspar surface in the pumice which is black on the top and turns dark-grey downward on the cross section at the Tianwen peak.Their structural features are described as follows.At the early weathering stages,small-sized solution openings and fissures were produced by dissolution at weak structures such as twin crystal and joint fissures.With increase of weathering dissolution,these dissolution products on the surface of feldspar became larger and emerged,controlled by the anisotropy of the feldspar crystals.For the earlier eruptive material(at lower level of strata),the dissolution degree is stronger and the structure is more complex.On the contrary,for the later eruptive material(upper level of strata),the dissolution is weaker and structure is simpler.It implies that the degree of weathering dissolution on the feldspar surface is correlated with ages of volcanic eruptions.Observations on the microstructure of feldspar surface suggest that the pumice at the Manjiang tree farm and the grey pumice at the Tianwen peak cross section are the product of the same one volcanic eruption.And the weathering dissolution degree of feldspar surface can be used as an indicator to determine the sequence of volcanic eruptions.Energy spectral analysis indicates that the fresh feldspar and that suffered from weathering dissolution have different chemical compositions.The microstructure and chemical composition of the feldspar that had experienced weathering dissolution resulted from a natural process of weathering,solution,leaching and precipitation.The element Fe in it is probably related with function of microorganism.The detailed analysis of weathering dissolution of feldspar surface can help study environmental change after volcanic eruptions and extimate their time sequence.

EXPERIMENTAL STUDY ON STICK-SLIP PROCESS OF BENDING FAULTS

GUO Yan-shuang, MA Jin, YUN Long

2011, 33(1): 26-35. DOI: 10.3969/j.issn.0253-4967.2011.01.003

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The stick-slip process of pre-cut bending faults with a 5°angle at bending point between the two fault segments is investigated by use of fault displacement measurement,strain tensor analysis and acoustic emission(AE)technique in the laboratory.The dynamic process and corresponding properties of physical evolution are discussed.The experimental results from bending faults show that: 1)A negative relationship was revealed between the logarithms of the stick-slip cycle and the logarithms of loading rate; 2)Under different loading rate,most of instabilities of bending faults are earthquake doublets,and the interval time between the two sub-events are primarily from 100ms to 200ms; 3)For different observational approaches,even if with the same sampling rate,the differences of the coseismic response were observed,such as the significant strain weakening stage indicated by strain measurements,but there was no significant change in fault displacement before fault instability; and 4)AE sources obviously migrated along faults during fault sliding.More dynamic information about fault instability process is needed to know the mechanism of strong earthquakes and the features of aftershocks.

A PRELIMINARY STUDY ON ASSESSMENT METHOD OF ABSOLUTE EARTHQUAKE EMERGENCY RESPONSE ABILITY AT COUNTY LEVEL

DENG Yan, NIE Gao-zhong, SU Gui-wu

2011, 33(1): 36-44. DOI: 10.3969/j.issn.0253-4967.2011.01.004

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The absolute earthquake emergency ability at county level is directly related to the effectiveness of the whole earthquake emergency response of China.This paper firstly analyzes the definition of absolute earthquake emergency response ability at county level,and then,based on the field survey of earthquake emergency response ability at county level after the Wenchuan earthquake,constructs preliminarily the index system for evaluating the county-level absolute earthquake emergency response ability and the comprehensive assessment.Finally,taking the counties and cities of Sichuan Province as example,the paper constructs the evaluation index system,which includes one object layer,five rule layers,nine factor layers and seventeen variable layers.Meanwhile,it puts forward comprehensive assessment method based on principal components analysis and multifactor comprehensive analysis.This method will help to assess quantificationally the absolute earthquake emergency response ability at county level,thus strengthening the ability of the county government in the management of earthquake emergency response.

METHOD OF LOCATING BURIED ACTIVE FAULT BY COMPOSITE DRILLING SECTION DOUBLING EXPLORATION

LEI Qi-yun, CHAI Chi-zhang, MENG Guang-kui, DU Peng, WANG Yin, XIE Xiao-feng

2011, 33(1): 45-55. DOI: 10.3969/j.issn.0253-4967.2011.01.005

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In this paper,an optimized drilling exploration method,the doubling section method,was summarized after many composite drilling section explorations of buried active fault in urban areas.Operation steps of this method are as follows: Firstly,drill a borehole at each of the two ends of the drilling section to make sure that fault is between the two boreholes,then,drill the third borehole at the middle of the two holes; and secondly,confirm again the segment where the fault is and drill the next borehole in the middle of it.By repeating the similar practice,the accurate location of fault can be constrained progressively.Meanwhile,this paper also uses a quantitative indicator,the key horizon gradient between two boreholes,instead of stratigraphic throw,to determine the location of buried fault and puts forward two criterions: 1)the fault is located between two boreholes if the key horizon gradients between these two boreholes are positive and increase with depth; and 2)the fault is located where the key horizon gradients between two boreholes increase obviously relative to the previous values and that of adjacent segments,besides the increase with depth.While in contrast,the key horizon gradient in a normal fault segment decreases obviously.Application cases show that the method can determine precisely the location of buried active fault.

SURFACE DEFORMATION OF THE WANGJIAGOU FAULT SET IN URUMQI AND THE SAFETY DISTANCE FROM IT

WU Chuan-yong, SHEN Jun, SHI Jie, LI Jun, XIANG Zhi-yong

2011, 33(1): 56-66. DOI: 10.3969/j.issn.0253-4967.2011.01.006

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The Wangjiagou Fault set,a set of Holocene active faults,is located at western suburbs of Urumqi City.The faults dislocated the gravel platform of the mid Pleistocene and the third level terrace of the Wangjiagou east bank,generating apparent fault scarps of opposite-slope direction on the surface with clear geomorphic traces.There are a series of deformation indications on landform,such as seismic fault,scarp and upheaval.In the field,thirty-nine groups of data were measured by using line tape along the fault.Among them,six were measured on the third level terrace of the Wangjiagou,and the others on the mid Pleistocene platform.Based on the data measured across the fault,we obtain that the height of the scarps is 0.4～1.6m and the width of the fault deformation is about 50m on the third level terrace.And on the mid Pleistocene platform,the height of scarps is 1.5～5.0m and the width of the deformation is about 90m.After comparing the profile of strong topographic deformation zone with the trench section,we primarily recognize that the ratio of hanging wall to foot wall deformation width is 2: 1approximately.The widths of strong surface deformation belt on the mid Pleistocene platform and the third level terrace on the two walls are 60m,30m and 33m,17m,respectively.

SPATIAL DISTRIBUTION AND ACTIVITY OF XUZHOU FEI HUANGHE FAULT ZONE

CHEN Ding, ZHANG Jing-fa, ZHU Lu, JIANG Wen-liang, LU Xiao-cui, LIU Jian-da, LI Li-mei, ZHANG Peng

2011, 33(1): 67-78. DOI: 10.3969/j.issn.0253-4967.2011.01.007

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Based on the remote sensing images interpretation,the spatial distribution of the Fei Huanghe(the ancient Yellow River)fault zone in Xuzhou area was studied and the intersection relationships between Fei Huanghe Fault and Shaolou Fault,and Tan-lu Fault were discussed in the paper.Besides,we researched the deep-seated geometric structure of Fei Huanghe Fault by studying the gravity-magnetic data,and discussed the intersection relationships with the west boundary of Tan-lu Fault. The cutting depth of Fei Huanghe Fault reflected by second order-wavelet transform detail of the Bouguer gravity anomalies is up to 7～8km.The depth reflected by the third order-wavelet and fourth order-wavelet transform detail of the Bouguer gravity anomalies is up to 9～11km and 15～18km,respectively.The results show that the Fei Huanghe Fault extends to Jiuding in southeast direction.The cutting depth is up to 8～9km.The NW-trending Fei Huanghe Fault cut the NE-trending Shaolou Fault,resulting in the change of the tectonic line of the latter from striking N 60°E to N 45°E.Moreover,the Fei Huanghe Fault didn't cut the Tanlu Fault.It is a pre-Quaternary Fault with weak activity.

THE SEGMENTATION OF RUPTURE AND ESTIMATE OF EARTHQUAKE RISK ALONG THE NORTH MARGIN OF WESTERN QINLING FAULT ZONE

SHAO Yan-xiu, YUAN Dao-yang, WANG Ai-guo, LIANG Min-jian, LIU Kun, FENG Jian-gang

2011, 33(1): 79-90. DOI: 10.3969/j.issn.0253-4967.2011.01.008

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We divide the north margin of Western Qingling Fault zone into six segments on the basis of new geology data,namely,Baoji,Tianshui,Wushan,Zhangxian,Huangxianggou and Guomatan segment from east to west.Each segment not only can rupture independently,but also can rupture together with others.The probability of seismic potential on these six segments and two combination segments is computed with the time-dependent seismic potential probability estimate method.We find from the result that,both the Huangxianggou and Zhangxian segments have the biggest probability of rupture in the future; and Tianshui segment is the second.If there will be a combined rupture,it is most likely to happen in Huangxianggou and Zhangxian segments,both of which have higher earthquake risk.We also compute b value along the fault zone.The image of b value indicates a high accumulated stress on the Huangxianggou and Tianshui segments.So we suppose that the two areas are the main locations where strong earthquakes may occur in the future.

STUDY ON RECENT TECTONIC STRESS FIELD IN YUNNAN REGION

QIAN Xiao-dong, QIN Jia-zheng, LIU Li-fang

2011, 33(1): 91-106. DOI: 10.3969/j.issn.0253-4967.2011.01.009

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In this paper,using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas,and based on the statistical analysis of the parameters of focal mechanism solutions,we discussed in detail the earthquake fault types and the characteristics of modern tectonic stress field in Yunnan region.The results show that most moderate-strong earthquakes occurring in Yunnan region are of the strike-slip type,amounting to 80%of the total.Normal faulting and normal with strike-slip and reverse and reverse with strike-slip earthquakes are almost equivalent in proportion,about 8%each,respectively.The tectonic stress field of Yunnan region is near-horizontal,and the dips of earthquake fault planes are large.There are three main dynamic sources acting in Yunnan region: one is the NE,NNE and NNW directed acting force from Burma,Laos and Vietnam; the second is the SE-SSE directed force from Sichuan and Sichuan-Yunnan rhombus block; and the third is the NW-NNW directed force from South China block.These three acting forces have controlled the faulting behavior of the main faults and the characteristics of activity of strong earthquakes in Yunnan and its adjacent regions.

ANALYSIS ON THE EVOLUTION OF SEISMIC VELOCITY STRUCTURE AT THE SOUTHERN END OF TAIHANG MOUNTAINS FAULT ZONE

ZHOU Jun-jie, WANG Yu, ZHANG Jing-sen, ZHOU Long-quan

2011, 33(1): 107-113. DOI: 10.3969/j.issn.0253-4967.2011.01.010

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The activity of fault is one of the causes of earthquakes.The distribution of the velocity structure of small earthquakes on the fault structure can offer an accurate underground crust structure model for us to analyze the activity of fault.Using the seismic network monitoring data at the southern end of the Taihang Mountains and the small earthquake P wave travel time data,the paper reconstructs the three-dimensional velocity structure model for the southern end of the Taihang Mountains Fault zone by joint inversion of seismic source and velocity structure.The results show: on the west of Taihang Mountain piedmont fault zone,there exists a NNE-trending fault.Horizontal distribution shows a zonal distribution of low velocity zone along the fault zone.The thickness of the sedimentary layer in Taihangshan uplift has reduced gradually from approximately 8km to about 2km,while under the force from the western side,the crust thickens gradually.

PRIMARY STUDY ON CODA Q VALUE IN LONGGANG VOLCANO AREA

LIANG Guo-jing, LI Zhong-wei, ZHENG Shuang-feng, LIU Jun-qing, LIU Da-feng, QI Wei

2011, 33(1): 114-122. DOI: 10.3969/j.issn.0253-4967.2011.01.011

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According to Sato(1977)single scattering model and using 41 earthquakes with M_L≥1.6 in the Longgang volcano and the nearby regions recorded by Longgang volcano digital seismic network from 2007 to February 2010,the coda Q value in the Longgang volcanic region was determined.All of events used in this paper occurred at depths from 6 to 10km,with the epicentral distances less than 75km.The results show that the coda Q has a dependence with frequency as Q(f)=(41.65±11.74)f^{(0.845 9±0.164 2)},which is characteristic of coda in active volcanic regions as low Q value and high η value.Compared to other volcanic areas in the world,the average Q_c of the Longgang volcanic area is obviously lower.Distribution of coda Q value on Longgang volcano shows that coda Q₀ value at Jinchuan seismic station near Jinlongdingzi volcano is 31.98,significantly lower than other stations’,which,in combination with the deep seismic sounding data and vertical deformation data,proves that the magma chambers probably locate in the vicinity of Jinlongdingzi volcano.For the lower coda Q₀ value,we interpret the strong attenuation of coda waves near the Longgang volcano is possibly related to high temperature medium caused by magma chambers.

THE GEOCHEMICAL CHARACTERISTICS OF SOIL GAS IN THE SOUTHEASTERN PART OF HAIYUAN FAULT

ZHOU Xiao-cheng, WANG Chuan-yuan, CHAI Chi-zhang, SI Xue-yun, LEI Qi-yun, LI Ying, XIE Chao, LIU Sheng-chang

2011, 33(1): 123-132. DOI: 10.3969/j.issn.0253-4967.2011.01.012

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The concentration of soil gas He, H₂, N₂, O₂, CH₄, C₂H₆, Rn, Hg and flux of soil gas He, H₂, CH₄, Rn, Hg were surveyed at four sites(Xiaokou,Bazhiyao,Caixiangpu and Xiaonanchuan)in the southeastern part of Haiyuan Fault.Soil-gas concentrations of more than 200 samples were obtained.The results show that the background values of N₂/O₂,Hg,Rn were 4.2,50.4ng/m³and 5.8k Bq/m³,respectively. The maximum concentrations of He and CH₄ were 65.3 and 537.7ppm,respectively,at the end of the southeastern part of Haiyuan Fault.Furthermore,soil gas He and CH₄ were intensively degassed.The maximum flux of He and CH₄ in soil gas was 6.9and 390mg m^-2d^-1,respectively.These may be caused by stress concentration at the end of the southeastern part of Haiyuan Fault.H₂ and Rn in soil gas were powerful components as indicators of location of the southeastern part of Haiyuan Fault.The maximum concentrations of H₂ and Rn in soil gas were 369.7ppm and 38.3k Bq/m³ near the middle of the southeastern part of Haiyuan Fault.The maximum fluxes of H₂ and Rn in soil gas were 5.5mg m^-2d^-1 and 828.6m Bqm^-2s^-1,respectively.These may be related with the intensive rupture of the middle of the southeastern part of Haiyuan Fault.The anomalies of Hg in soil gas at the fault were good reference indicators.The maximum flux of Hg in soil gas was 211.2ng m^-2h^-1.

WELL WATER LEVEL CHANGE WITH TIDE GENERATING HEIGHT FOR LINEAR POROELASTIC AQUIFER AND THEIR APPLICATION

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

2011, 33(1): 133-140. DOI: 10.3969/j.issn.0253-4967.2011.01.013

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Volume strain for the saturated rock in the undrained condition under tide force is studied in this paper with mechanical balance equation of linear elastic medium.The equation relating to pore pressure in confined aquifer responding to tide generating height(TGH)is proposed,and the coefficient(E) in this equation is defined with a clear physical meaning.In combination with the formula proposed by Hsieh(1987) for the amplitude ratio (A) and phase shift (α₁) of well water level response to pore pressure,the formula is derived for the amplitude ratio M(=EA)and phase shift α(=α₁+α₂) of well water level response to TGH.M and α can be calculated by measured water level and theoretical earth tide data.Assuming the phase shift(α₂) of pore pressure to TGH approximates zero,the transmissivity(T)of the aquifer,the amplitude ratio(A)and response coefficient(E) can be in turn determined by M and α.As an example,Chuan 18and 06 well data are used to calculate M and α, and to estimate T,A and E,and the changes of A,E and M with T are analyzed.

THE SIGNIFICANCE OF DISCOVERY ON HOLOCENE ACTIVITY ON THE YILAN-YITONG FAULT IN NORTHEAST CHINA

MIN Wei, JIAO De-cheng, ZHOU Ben-gang, SHENG Jian, CHEN Tao

2011, 33(1): 141-150. DOI: 10.3969/j.issn.0253-4967.2011.01.014

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No earthquake greater than M6 has been documented on the Yilan-Yitong Fault,and no trace of activity since the late pleistocene has been seen either at the northeastern section of the famed Tanlu grand fault zone in eastern China.Thus this fault is recognized active in the early Quaternary and capable of generating moderate quakes.By analyzing high-resolution satellite images and field work,a 70km-long geomorphic scarp in Tonghe County of Heilongjiang Province and a 10km-long geomorphic scarp in Shulan County of Jilin Province were discovered.The scarps are 1～2m high and offset the young terraces.Subsequently,the trench at Tonghe County revealed fault displacement which almost reaches the surface.The uppermost stratum dislocated by the fault is dated to be 1730±40 years B.P.Analysis of geomorphic feature of the fault scarp and the trench profile suggests that an M≥7 paleoearthquake occurred along the fault since 1730±40 B.P.The trench at Shulan County reveals the faulted late Pleistocene stratum covered by stratum dated to be 2360±40 years B.P.All these data suggest that some segments of Yilan-Yitong Fault are active since Holocene and M7 earthquake occurred.So,further detailed research will be necessary to determine the range of the latest activity of this fault,the time of the rupture and recurrence intervals of major earthquakes.These data will be of great significance for earthquake zonation and assessment of seismic risk in this region.

MONITORING OF INJECTION-INDUCED SEISMICITY AT RONGCHANG,CHONGQING

WANG Xiao-long, MA Sheng-li, LEI Xing-lin, YU Guo-zheng, WANG Qiang, GUO Xin, KUWAHARA Yasuto, IMANISHI Kazutoshi

2011, 33(1): 151-156. DOI: 10.3969/j.issn.0253-4967.2011.01.015

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Rongchang area had exhibited low levels of natural seismicity,and there was no record of earthquake with M_L>5 in the history.However,following the injection of unwanted water from gas production,seismicity has increased dramatically and showed progressive increase of magnitude since July 1988,and an earthquake of M5.2 occurred in 1997.Rongchang area is thus an ideal site for studying seismicity induced by deep well injection.Unfortunately,there was only one seismic station in the area,and the research was limited by the poor detectability and hypocenter location accuracy.In order to make a thorough investigation on the injection-induced seismicity in the area,a temporal seismic network was installed in July,2008 under the cooperation of the State Key Laboratory of Earthquake Dynamics,Geological Survey of Japan and Chongqing Earthquake Administration.The seismic network consists of 6 stations,by which waveforms are continuously recorded.As a result,both the detectability and location accuracy are improved greatly.This paper presents a brief summary of the cooperative project and some preliminary results of recent seismicity in the area.

INSAR COSEISMIC DEFORMATION OBSERVATION OF THE JAN 12^TH,2010 HAITI EARTHQUAKE AND ITS COESEISMIC SLIP DISTRIBUTION INVERSION

XUE Lian, SUN Jian-bao, SHEN Zheng-kang

2011, 33(1): 157-174. DOI: 10.3969/j.issn.0253-4967.2011.01.016

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At 21: 53(GMT)on Jan 12th,2010,an M_W 7.1 earthquake struck Haiti with epicenter located at(72.57°W,18.44°N).We derive the high precision Interferometric Synthetic Aperture Radar(InSAR)deformation field covering the whole rupture zone and use the observations to study the seismogenic kinematics of the quake.We analyze the influences of InSAR data errors,such as the orbit errors and atmospheric errors,on the ALOS PALSAR data and finally obtain the coseismic deformation field in the line of sight(LOS)direction.We invert the LOS displacement for the fault geometry of the seismogenic fault and its corresponding slip distribution.We find that the fault dips to the north at 37°,lower than the 70° north-dipping solution from USGS.To test other possible dipping angles of the fault plane and find the best estimate of the fault geometry,we construct an other two fault models.One is modeled with a 70° north-dipping fault plane and the other one is a listric fault model with the hinge depth inverted.Comparing the predicted InSAR interferogram of the three fault models with the observed InSAR coseismic data,we argue that the model with 37° north dipping angle is more rational than the other two models.Our preferred model shows that the coseismic slip concentrates mainly at 4～16km depth,and the maximum slip is 2.8m,appearing at 7.2km depth.The coseismic displacement exhibits both reversal faulting and sinistral strike-slip,suggesting complex fault motion in this earthquake.The moment release of this earthquake is 5.64×10¹⁹ Nm,equivalent to an M_W 7.1 earthquake.

STUDY ON THE RELATIONSHIP BETWEEN THE RESERVOIR-INDUCED SEISMICITY AT ZIPINGPU RESERVOIR AND THE M_S 8.0 WENCHUAN EARTHQUAKE

MA Wen-tao, XU Chang-peng, ZHANG Xin-dong, XU Xi-wei, LI Hai-ou, YUAN Jing-li

2011, 33(1): 175-190. DOI: 10.3969/j.issn.0253-4967.2011.01.017

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Using the observations of the Zipingpu reservoir seismic network(including seven short-period seismic stations,with an average station distance of 10km)of the period from July 2004 to 2009,and the data from January-December 2009 recorded by the intensive seismic observation network(six short-period seismic stations with the station spacing of 3km),930 foreshocks near Zipingpu reservoir,the main shock,and 5789aftershocks,as well as the initial rupture of the M_S 8.0 Wenchuan earthquake were relocated with double difference location algorithm.Combined with the geological field investigations,the analysis of seismic activity in Zipingpu reservoir area,the distribution of coseismic surface rupture,the depth of initial rupture location of Wenchuan M_S 8.0 earthquake,and the aftershock distribution,we find that the occurrence of M_S 8.0 Wenchuan earthquake has close relation with Zipingpu reservoir: 1) The seismic swarms at the Shuimo,and Dujiangyan and Shenxigou area are 10 kilometers away from the reservoir,the seismic strain release caused by Zipingpu reservoir increased by 200%,and the release was closely related to water level changes and accelerated before the Wenchuan earthquake; 2) There are two northeast directed coseismic surface rupture zones with 1m displacement along Zhongtanpu Fault; 3) the aftershocks of Wenchuan earthquakes are mainly distributed on northwestern wall of the Zhongtanpu Fault; 4) The relocation revealed that the Wenchuan earthquake occurred at 27minutes,59.5 seconds,the depth is between 6～9km; and 5) by comparison,the focal depths of the fore-shocks occurring on 2008-04-05 are about 7.8km,and the initial time of waveforms of this swarm is same as that of the M_S 8.0 Wenchuan earthquake.

ANALYSIS OF LANDSLIDES TRIGGERED BY WENCHUAN EARTHQUAKE

CHEN Xiao-li, DENG Jian-liang, RAN Hong-liu

2011, 33(1): 191-202. DOI: 10.3969/j.issn.0253-4967.2011.01.018

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On May 12,2008,a huge earthquake(M_S=8.0)named Wenchuan earthquake hit Sichuan Province in Southwest China and triggered thousands of landslides.Post-seismic investigation and analysis discovered some characteristics of the landslides' spatial distribution.Landslides occurred unevenly on both sides of Longmenshan Fault zone,which are reverse faults and responsible for the Wenchuan earthquake.The majority of the landslides are distributed on the hanging wall of Longmenshan central fault,while only 12%of the total occurring on the footwall.The higher density of landslide is located at both ends of the Longmenshan Faults as well as the middle section.Statistical studies also show the occurrence of landslides has close relationship with ground motion,slope gradient and rock properties and so on.The geological background and evolution history of Wenchuan earthquake region have controlled the local geological and topographical setting and affected the landslide distribution when the great earthquake took place.Due to the exceptionally high topographic gradient and geological features such as loose soil and fragile rocks,this region is notoriously prone to landslide.

QUAKEPROOF DISASTER REDUCTION: FORECAST NEXT MACROSEISM LOCATION AND IMPLEMENT CORRESPONDING EARTHQUAKE RESISTANCE FORTIFICATION OF REGIONAL CONSTRUCTIONS

CAI Zuo-xin

2011, 33(1): 203-207. DOI: 10.3969/j.issn.0253-4967.2011.01.019

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