Table of Content

19 March 2010, Volume 32 Issue 1

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Brief Report

FEATURES AND TECTONIC IMPLICATIONS OF THE NORTHEASTERNMOST SURFACE RUPTURE OF WENCHUAN M_S 8.0 EARTHQUAKE ON THECENTRAL FAULT OF LONGMENSHAN FAULT ZONE

AN Yan-fen, HAN Zhu-jun, DONG Shao-peng, XU Xi-wei

2010, 32(1):  1-15.  DOI: 10.3969/j.issn.0253-4967.2010.01.001

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The kinematic property of the Wenchan earthquake's surface rupture changes from strike-slip with slightly smaller dip-slip component to the dominant dextral strike-slip at the northeasternmost region between Shikan in Pingwu county and Woqian in Qingchuan county,where,the dip-slip component is reverse between Shikan and Pingxi,normal at Kuangpingzi and its north,with no compressive deformation observed,and it turns to dextral strike-slip near Woqian.The width of the surface deformation zone is less than 10m on this segment.At Dongjia,a village north of Woqian in Qingchuan,the seismic surface rupture zone mainly exhibits as extensional fissures and graben-like negative landform,which are the products of accommodation of the heterogeneous stress and strain at the tip portion of the seismic surface rupture.The width of the surface deformation zone is about 10～12m.No surface rupture evidence was found at Donghekou village in Qingchuan county,so we infer that the surface rupture zone didn't spread through the Qingshui River flowing along the three villages of Donghekou,Guanzhuang and Liangshuijing in Qingchuan county and the structural geomorphology reflects variant vertical motion.Evidence for dextral strike-slip motion was hardly found.The whole length of the rupture zone on the central fault is around 240km.In the course of the Wenchuan earthquake,the tectonic deformation on the surface along the central fault was adjusted within the range of the central fault,and didn't transfer to the external regions.

SIMULATIONS ON DISPLACEMENT FIELDS OF GROUND SURFACE IN 2008 WENCHUAN EARTHQUAKE:THE CASE OF INVERSE AND RIGHT-LATERAL MOTION OF YINGXIU-BEICHUAN FAULT

BAI Yu-zhu, XU Jie, XU Xi-wei, ZHOU Ben-gang, CHEN Guo-guang

2010, 32(1):  16-27.  DOI: 10.3969/j.issn.0253-4967.2010.01.002

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Basing on the fault dislocation model of Yoshimitsu Okada and Steketee and filed scientific investigation,we calculate theoretically space variation of the displacement fields,including vertical and horizontal displacements of the Wenchuan earthquake along the near zone(within 30km to the fault)of Yingxiu-Beichuan reverse fault.In the simulation,we interpret the space variation of the displacement field in the near zone of Yingxiu-Beichuan reverse fault in details.However,we can't describe the space variations in much detail by the field scientific investigation and limited data of GPS stations.Comparing with the results of field science investigation on surface rupture zone,our computational results show that the displacement fields have the same variation trend.At the same time,the displacement field declines drastically with distance to the outcrop of the fault,which agrees with the present research,and the velocity of this decline is much faster on the foot wall of fault than that on the hanging wall.By the simulation,we get the main conclusions:the vertical displacement of ground surface resulting from faulting in the earthquake shows the strong spatial inhomogeneity,and most large values of vertical displacement concentrate on the terminals of the fault,i.e.nearby Yingxiu and Beichuan.The displacement of the ground surface,including horizontal and vertical component,varies more drastically on both terminals of the fault than that of the middle section of the fault.The vertical displacement changes drastically along the direction of strike in the hanging wall of the fault than that of the foot wall.Except on the terminals of the fault,the horizontal displacement distributes homogenously in space.On the whole,except on the terminals of the fault,the amplitude of the displacement field on the hanging wall of the fault is larger than that of the foot wall.

YANSHAN AND GAOSHAN VOLCANOES IN THE DAXINGAN MOUNTAIN RANGE-A NEW ERUPTION STYLE

ZHAO Yong-wei, FAN Qi-cheng

2010, 32(1):  28-37.  DOI: 10.3969/j.issn.0253-4967.2010.01.003

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Yanshan and Gaoshan,two Holocene volcanoes in the Halaha River and Chaoer River volcanic cluster,are different from volcanoes with Strombolian eruption.Their early-stage eruptions produced pyroclasts which formed scoria cone,tephra fall-out sheet and small-scale pyroclastic flow,while the late stage eruptions effused a great amount of lava.They have large cones with the elevation above 200～300 meters,and the cones are made up of cinder cone and spatter cone.Tephra fall-out sheet is around the cones.The effused lava flow from the two volcanoes underwent the lava type transition from pahoeoe lava to aa lava.According to the characteristics of volcanic products,the eruption style is presented as follows:explosive eruption with a sustained eruption column,Strombolian eruption,lava fountain eruption.The sustained eruption column characterizes the new style and makes it different from typical Strombolian eruption.The similar eruption as Yanshan and Gaoshan happened in Longgang Quaternary volcanic cluster and Holocene volcanic cluster in Jingbohu.It is a new eruption style in the continental volcanism in China.

STUDY ON LONG-PERIOD MAGNETOTELLURIC SOUNDING——THE LMT TRANSFER FUNCTION IN EASTERN TIBETAN PLATEAU

XIAO Peng-fei, BAI Deng-hai, Ivan. M. Varentsov, LIU Mei, KONG Xiang-ru

2010, 32(1):  38-50.  DOI: 10.3969/j.issn.0253-4967.2010.01.004

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As a complement to conventional MT,Long-period Magnetotellurics("LMT") has been developed at low frequency for soundings of deep electric structures.Due to the thick and low resistive crust and upper mantle in east Tibetan Plateau,the conventional MT could not provide sufficient information about deep structures of the study area that requested long period MT measurement to be complemented.This paper presents brief introduction of LMT in respect of the concept,data acquisition,processing,modeling,inversion and interpretation.Most important is that practical LMT sounding applied in eastern Tibetan Plateau gives the LMT transfer functions of impedance and tipper,which coincide with conventional MT.The result of the LMT profile illustrates the wide distribution of high-conductivity layers and provides more information about the base of the conductors beneath the eastern Tibetan Plateau,with higher resolution.Anomalous induction coefficients and 2-D model suggest extensive conductive bodies beneath Lhasa block and Qiangtang terrain which would be a possible evidence for partial melt and fluids at depth.

THE ELECTRICAL CONDUCTIVITY STRUCTURE OF THE EASTERN TIBETAN PLATEAU AND ITS TECTONIC IMPLICATIONS

LIU Mei, BAI Deng-hai, XIAO Peng-fei

2010, 32(1):  51-58.  DOI: 10.3969/j.issn.0253-4967.2010.01.005

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A new MT study was conducted along the profile EHS3D-3(Xiachayu of Tibet-Qingshuihe of Qinghai)in 2007.The preferred 2-D model suggests that:1)the upper crust consists of separated resistive blocks;2)in mid-lower crust there is an extensive conductor beneath Lhasa block and Qiangtang terrain respectively due to aqueous fluids and/or partial melts and are inferred to as crustal flow channels at depth of Tiebtan Plateau;3)Yarlun-Zangbo and Bangonghu-Nujiang sutures are indicated by two conductive layers dipping to the north;4)Jinshajiang Fault might be a fracture belt of upper crust that was thinned and destructed by the upwelling of the hot/conductive body at depth.

DOES ALIGNMENT OF MELT ENHANCE SEISMIC ANISOTROPY BENEATH TIBET?

YANG Yu, CHEN Jian-ye, YANG Xiao-song, YAN Xiao-bing, ZHANG Guo-linguan

2010, 32(1):  59-69.  DOI: 10.3969/j.issn.0253-4967.2010.01.006

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It is commonly agreed that seismic anisotropy,most likely caused by aligned minerals,is a very important indicator of intracrustal deformation.Ultrasonic velocity measurements on the schists,gneisses,migmatites,amphibolites and mylonites from Higher Himalayan Crystallines(HHC) and Honghe strike-slip fault zone in the southwestern China show that the average anisotropic magnitude of them is about 5%,which is much less than that observed by a series of measurements of surface-wave dispersion inversions and waveform inversions of P to S conversions in these regions.Modeled results indicate that seismic anisotropy can be enhanced by alignment of melt.For instance,extra anisotropy of 2%～10% for P-wave velocity and of 2.2%～40% for S-wave velocity would be induced by melt pocket preferred orientation when aspect ratio of melt pockets and melt fraction range from 0.1 to 0.5 and from 5% to 10% respectively.Obviously,the contribution of aligned melt to the anisotropy is likely comparable to or larger than that induced by lattice preferred orientation of major minerals.Geophysical investigations demonstrate that Tibetan and Sichuan-Yunnan crust is characterized by high geothermal gradients and abnormal thickness.Low degree partial melting accounting for low average crustal velocity and low velocity zones is present in the crust pervasively.Hence,we attribute the extremely high anisotropy observed within Tibetan and Sichuan-Yunnan crust to aligned melt pocket induced by localized deformation.It implies that the anisotropy zones within Tibetan and Sichuan-Yunnan crust is one of candidates to cause the upper part of crust(crustal block)to decouple to the other part of lithosphere.

DISCUSSION ON THE CHARACTERISTICS OF REGIONAL TECTONIC STRESS FIELD OF XINJIANG FROM 2003 TO 2008

GAO Guo-ying, NIE Xiao-hong, LONG Hai-ying

2010, 32(1):  70-79.  DOI: 10.3969/j.issn.0253-4967.2010.01.007

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The paper presents the focal mechanism solutions of 74 earthquakes with M_S≥4.5 from 2003 to 2008 in Xinjiang and analyzes the regional stress field characteristics reflected by these focal mechanism solutions in Xinjiang in this period.Then,discussion has been made combining with the seismicity image and regional stress field from 1990 to 2008.The result shows that,spatial seismic activity patterns of earthquakes with M_S≥5 in Xinjiang are quite different between 1990-2003 and 2004-2008.The seismic activity of mid-strong earthquakes or larger from 1990 to 2003 concentrated in the Aletai seismic belt,the eastern Tianshan mountains and the Arjin-Kunlun mountains tectonic belt.During this period,there occurred respectively the M_S7.3 Zaisang earthquake in June,1990,the M_S7.8 Mani earthquake in 1997,the M_S8.1 west of Kunlun mountain pass earthquake in 2001and the M_S7.9 earthquake in the border area between China,Russia and Mongolia in 2003.Since 2004,the seismic activity of mid-strong earthquakes showed a trend of decreasing towards west in Xinjiang.The azimuth of the principal compression stress P axis of focal mechanism solutions is NNW,which is slightly different from the background stress field of near SN and the earlier result of NNE obtained by the author.It reflects the changing characteristic of the large-scale regional stress field in different times in Xinjiang.The inversion result of three regional stress fields reveals some difference in space.The middle area of Tianshan mountains is obviously under the stress field of NNW direction;In the west of South Tianshan mountains-Wuqia and Hetian area and its surroundings,the principal compression stress has the characteristic of NE.The change of elevation angles of the principal compression stress P axis in the focal mechanism solutions of mid-strong earthquakes is obviously related with the strong and weak seismic activities in Xinjiang.

A STUDY ON THE QUATERNARY ACTIVITY OF TIANJIN FAULT

SHAO Yong-xin, LI Zhen-hai, CHEN Yu-kun, REN Feng, YAO Zheng-quan

2010, 32(1):  80-89.  DOI: 10.3969/j.issn.0253-4967.2010.01.008

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Tianjin Fault includes south Tianjin Fault and north Tianjin Fault.Based on the results of artificial seismic exploration,four borehole profiles were laid out respectively at west of Jinghai county town,Chaomidian village of Xiqing district,Xiaonanhe village of Xiqing district,and Zhutoudian village of Ninghe county to implement the exploration of these faults.Through identification of microfossils,the locations of marine strata in boreholes were obtained in this work,and through stratigraphic dating,the ages of the first,second and third marine strata were determined.Through strata contrast with the marine strata as key marker horizons and integrating with the test results of paleo geomagnetism of BZ2 and TN3 bores,the activity of north Tianjin North and south Tianjin Fault was analyzed.The result indicates that there have been no signs of movement of the south Tianjin Fault since late Pleistocene,and it might have weak activity before middle Pleistocene.No sign of activity of the north Tianjin Fault has been found since late Pleistocene either,and it might be active in the early stage of early Pleistocene.These show that the activity of the south Tianjin Fault is stronger than that of the north Tianjin Fault.At the same time,we find that the second,third and fourth marine strata are lacking to some extent in different areas.So,before they are used in strata contrast,the age of marine strata must be determined,otherwise the results of strata contrast may lead to mistake.For the second marine stratum,where there has been dispute about its age,we consider the age is about 70ka or so.

THE ANALYSIS AND RESEARCH OF TRANSIENT ELECTROMAGNETIC CONFIGURATION OF SMALL MULTI-TURN COINCIDENT LOOP

ZHANG-Hua, CAO-Jun, SUN Hai

2010, 32(1):  90-97.  DOI: 10.3969/j.issn.0253-4967.2010.01.009

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Using experimental techniques,the paper investigates the transmitted magnetic moment,the turn-off time,and the change of induced signal with the turns of the transmitter and receiver loops of multi-turn small coincident configuration,respectively.Comparison is made between the two experimental methods,i.e.changing the receiver loop turns with fixed transmitter loop turns and vice versa,to find out the turns more suitable to geological response.Meanwhile,comparative test is done using the wire frame of loop length of 0.5m?0.5m and 1m?1m,respectively.Through the analyses on the transmitted magnetic moment,the turn-off time,the relations of induced signal intensity with the loop turns and the length,we find the reasonable small multi-turn coincident loop configuration.The result indicates that the transmitted magnetic moment increases with the increased transmitter loop turns and length;the turn-off time increases proportionally with the transmitter loop turns,but has nothing to do with the receiver loop;and the induced signal intensity has a proportional relation with loop turns,with the receiver loop turn to be dominant,comparatively.

AN EXPERIMENTAL STUDY ON THE MECHANISM OF RAPID AND LONG RUN-OUT LANDSLIDE TRIGGERED BY WENCHUAN EARTHQUAKE

SUN Ping, WANG Fa-wu, YIN Yue-ping, WU Shu-ren

2010, 32(1):  98-106.  DOI: 10.3969/j.issn.0253-4967.2010.01.010

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The 2008 great Wenchuan earthquake caused multiple rapid and long run-out landslides,which resulted in a lot of deaths and property loss.Donghekou landslide,a typical rapid and long run-out landslide triggered by Wenchuan earthquake,is located in Qingchuan county,and at present,it is concerned and discussed particularly because of its complex original mechanism.Field investigations show that the original mechanisms and dynamic features mainly include the followings,for example,the shattering collapse,the horizontal slinging,the debris flow and the vibration liquefaction,etc.In order to simulate and reconstruct the vibration liquefaction,representative soils on sliding zone of Donghekou landslide were collected for soil tests.By using the advanced DPRI ring shear apparatus,a series of ring shear tests have been carried out to study the vibration liquefaction process of Donghekou landslide under the loading of real seismic waves,and some ideal results were gotten.The test results show that when the earthquake happened,the vibration liquefaction occurring on the potential sliding surface played an important role in generating the rapid and long run-out landslide.When the soils were dry,only a small displacement(0.007m)was generated,which couldn't form a landslide with high speed and long run-out;with the vibration liquefaction,the shear strength could be decreased and a large displacement could be generated,which supplied a necessary condition for the generation of rapid and long run-out landslide.

INTERPRETATIONAL CHARACTERISTICS OF OPTICAL REMOTE SENSING IMAGE FOR THE CO-SEISMIC SURFACE DEFORMATION OF THE 2008 WENCHUAN EARTHQUAKE AND ITS RELATIONSHIP WITH IMAGING

CHEN Gui-hua

2010, 32(1):  107-114.  DOI: 10.3969/j.issn.0253-4967.2010.01.011

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Data from remote sensing played important roles in the rescue during the 2008 Wenchuan earthquake and reconstruction after the great disaster.It also has much realistic significance to implement a rapid interpretation and geological study from those data.Analysis was made on the characteristics of optical remote sensing image,such as shadows and texture,and geological and geomorphological features of the surface rupture from field investigation.The interpretation marks of the post-earthquake optical remote sensing image were concluded for the fault scarp of the great Wenchuan earthquake.Based on the optical imaging,the shadow forming and interpretation characteristics of different kinds of fault scarp were analyzed for the Wenchuan earthquake.The imaging time and the occurrence of fault scarps make a constraint on the forming of shadows and its interpretation for fault scarps.Analysis based on characteristics of imaging and rupture styles gives a new insight on the limitation in the application of remote sensing data of co-seismic surface deformation,and also a certain proposal for the emergency aerial remote sensing in the future.

A DISCUSSION ON THE RETROSPECTIVE PREDICTION OF THE M_S 8.0 WENCHUAN EARTHQUAKE IN 2008 BY MEANS OF EARTHQUAKE SOURCE MODELS

GUO An-ning, GUO Zeng-jian

2010, 32(1):  115-126.  DOI: 10.3969/j.issn.0253-4967.2010.01.012

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The cause and prediction of great earthquake are very complicated.It is difficult to totally summarize them using one model.In the paper,we use four models to describe them,namely,the superposition model,the combination model,the stereographic cross model and the modulation model.Each of the four models plays a different role in describing the preparation and occurrence of an earthquake.The superposition model deals with the problem about the driving force of earthquake preparation.The combination model discusses the problem about the structure of earthquake source.The stereographic cross model discusses the problem of how the asperity on the fault plane in the seismic source forms.And the modulation model focuses on the problem about that external factors triggering instability in the source region and its vicinity during short and imminent term before an earthquake.The paper tries to make a retrospective prediction of the M_S 8.0 Wenchuan earthquake in 2008 using the abovementioned models.

CORRELATION ANALYSIS BETWEEN MODIS BRIGHTNESS TEMPERATURE AND SURFACE TEMPERATURE PROVIDED BY METEOROLOGICAL STATION

LIU Fang, LV Yi-Pei, JIANG Li-Meng, XIN Hua, ZHANG Tie-Bao, LU Qian

2010, 32(1):  127-137. 

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Through numerous comparison experiments and the correlation analysis at different time scales,the present study tried to get the important basis of statistic significance in aspect of the use of real-time relative changes of MODIS BT combined with field ST measurements from thermal infrared anomalies for directly investigating the short and imminent earthquake-related phenomena.Results of correlation analysis show that:1)Significant correlation exists between brightness temperature,air temperature and ground temperature in the view of the longer cycle time scale(monthly mean),even in the case of short cycle(daily means),where the correlation is significantly lower than that of longer cycle,they still have good correlations;2)The correlation between the mean brightness temperature and the surface temperature increases gradually with the increased pixel size involved.This indicates that the atmospheric and environmental effect on brightness temperature is more obvious for single pixel.Th

SEISMIC RISK QUANTITATIVE EVALUATION ON BLIND FAULTS IN TIANJIN AREA

CHEN Yu-kun, LIU Fang, YUAN Dun, LI Wen-dong, YANG Xu-lian, GAO Wu-ping

2010, 32(1):  138-149.  DOI: 10.3969/j.issn.0253-4967.2010.01.014

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Based on faults surveying and research data in Tianjin area,through studying tectonic structure,Quaternary activity,deep structure,stress and strain fields and seismicity on the Tianjin Fault,the activity and tectonic features of the fault are determined synthetically.Using seismo-geological data,and the historical and moderm seismicity data,the frequency-magnitude relationship model reckoning by 500years is established and the relationship between the upper limit of maximum magnitude M_mu and a_t/b is fit,which is applied to evaluating potential earthquake's maximum magnitude on moderately and weakly active blind faults in the fault sub-areas of the region.Then Poisson probability model is adopted and quantitative parameters such as the maximum magnitude,occurrence probability,recurrence period of the south Tianjin Fault in the coming 50～200 years are calculated.

ON THE CAUSES OF EARTHQUAKE-GENERATED TSUNAMI

WEI Bai-lin, HE Hong-lin, GUO liang-tian, YANG Xuan, KANG Ying

2010, 32(1):  150-161.  DOI: 10.3969/j.issn.0253-4967.2010.01.015

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Based on the study and statistics on earthquakes,we know that most of the earthquakes don't induce tsunami,so there is no direct causality between earthquake and tsunami.The earthquake-generated tsunami(especially the big earthquake-generated tsunami)is mainly induced by the secondary and huge volumetric submarine landslide and collapse caused by ocean-bottom earthquake,rather than the submarine coseismic dislocation and deformation.If there exist unstable submarine landslide and collapse bodies nearby the epicenter,earthquake,regardless of the size,the focal depth,or the source type(namely,dip-slip or strike-slip)of it,will induce submarine landslide and collapse,and then generate tsunami.Otherwise,it will not generate tsunami even with big magnitude or dip-slip.

ADVANCES IN APPLICATION OF FINITE ELEMENT NUMERICAL SIMULATION TO SEISMOGEOLOGY IN NORTH CHINA

HU Meng-qian, DENG Zhi-hui, LU Yuan-zhong

2010, 32(1):  162-173.  DOI: 10.3969/j.issn.0253-4967.2010.01.016

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The paper summarizes the application and development of finite element numerical simulation methods in the seismo-geological study in North China in the last 30 years,and the discussion is focused on the following three aspects:the finite element model for North China,actual data used in the simulation and numerical simulation results.The study of finite element numerical simulation in North China began in 1980,since then,it has experienced the phases of development from elastic to elastoplastic,viscoelastic and creep simulations,from 2D to 3D,from linear to nonlinear,from continuous deformation to discontinuous deformation,and from the use of individual data to the use of multiple synthetic data.It shows that finite element numerical simulation is an effective means for studying seismology and geology in North China,and distinguished results have been achieved by using simulation methods.The achievement will be the foundation for the future simulation study in North China.The paper also discusses the significance,existing problems and development tendency of finite element numerical simulation in seismo-geology in North China.finite element method,numerical simulation,North China.