Table of Content

09 September 2009, Volume 31 Issue 3

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Brief Report

WENCHUAN EARTHQUAKE M_S 8.0:PRELIMINARY STUDY OF CRUSTAL ANISOTROPY ON BOTH SIDES OF THE LONGMENSHAN FAULTS

QI Shao-hua, LIU Qi-yuan, CHEN Jiu-hui, LI Yu, LI Shun-cheng, Guo Biao, WANG Jun

2009, 31(3):  377-388.  DOI: 10.3969/j.issn.0253-4967.2009.03.001

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From the teleseismic P-waveform data recorded at the dense mega seismic array deployed in the western Sichuan area by the State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,we investigate the crustal anisotropy beneath the stations using waveform correlation method and weighted stacking method. As a preliminary result,we measured the fast polarization azimuth and time delay of the Ps converted wave in the receiver functions at 4 stations on both sides of Longmen Shan Faults. Our results show:1)The waveform correlation method is better than the weighted stacking method and it turns out not only the fast polarization azimuth,but also the time differences between the fast-and slow-wave; The results obtained by using the weighted stacking method are something undetermined due to that the symmetric axis of the crustal anisotropy medium is unclear previously; Application of both methods will be in favor of judging the reliability of the results. 2)The fast polarization azimuths are consistent each other at the stations in Sichuan Basin,suggesting the crust beneath Sichuan Basin has well integrality and a weak lateral deformation. 3)Taking the epicenter of the Wenchuan earthquake as a boundary,the fast polarization azimuth is parallel with the Longmen Shan Faults on the north side of the Sonpan-Ganzi block,and perpendicular to the faults on the south side. This suggests that under the obstruction of the Sichuan Basin,the soft lower crust beneath the north side of the Sonpan-Ganzi block has a NE direction extended deformation along the Longmen Shan Faults,and the crust on its south side is in the status of compressive deformation perpendicular to the faults. Our results can be used for interpreting the single-side rupture of the Wenchuan earthquake and the aftershock evolution.

STUDY ON THE ACTIVITY OF RED RIVER FAULT IN VIETNAM

ZHANG Jian-guo, HUANGFU Gang, XIE Ying-qing, PHAN Trong Trinh, LIU Na

2009, 31(3):  389-400.  DOI: 10.3969/j.issn.0253-4967.2009.03.002

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Correlated evidences about the newest activity of Red River Fault in Vietnam(RRFV),such as seismicity,geology,geomorphology and chronology etc,have been obtained through joint survey along the fault in Vietnam. Our comprehensive studies demonstrate that,the same tendency of gradual weakening of the fault activity from north to south in the part of China since Quaternary has been kept on in Vietnam. The primary active period of Red River Fault in Vietnam is in late of middle Pleistocene,and in general,the active level of Red River Fault is lower prominently than that in Yunnan,China,especially,the activity of RRFV has been very weak since late Pleistocene. The synthesized analysis on seismicity and regional GPS deformation monitoring data indicates that the dynamic impact of so-called lateral extrusion from Tibetan Plateau on the dextral slip of RRFV should be very limited. Furthermore,the possible reasons including geotectonic and deep crustal structure have been discussed in the article.

A STUDY OF SHEAR-WAVE SPLITTING IN THE CRUST BY LIAONING TELEMETRY SEISMIC NETWORK OF CHINA

TAI Ling-xue, GAO Yuan, SHI Yu-tao, WU Jing

2009, 31(3):  401-414.  DOI: 10.3969/j.issn.0253-4967.2009.03.003

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Using the seismic data recorded by Liaoning Telemetry Seismic Network(LTSN)of China from June 1999 to December 2004,the study analyzes data of 8 stations by Systematic Analysis Method(SAM)of shear-wave splitting technique. The results show that predominant polarization directions of fast shear-waves at most stations are in strike ENE(nearly E-to-W),consistent to the direction of regional principal compressive stress,and also consistent to the direction of the regional tectonic stress field in the north part of North China. However,the predominant polarization directions of fast shear-waves at station SJ in the middle of Liaoning and station KD in the southeast of Liaoning are in strike nearly N-S and NW,different from other stations,which may be controlled and influenced by the complex local geological structure. However,more data are needed to verify for details at these two stations. Also according to results from GPS,geological and geophysical data,the paper studies the regional distribution of faults and principal compressive stress directions,and discusses the spatial characteristics of shear-wave splitting in this zone.

K-Ar DATING OF JAROSITE IN EASTERN TIANSHAN AND ITS ENVIRONMENTAL SIGNIFICANCE

HE Wei, LI Da-ming, ZHENG De-wen, WAN Jing-lin, XU Ying-xia

2009, 31(3):  415-423.  DOI: 10.3969/j.issn.0253-4967.2009.03.004

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Eastern Tianshan area is an extremely arid desert zone,with the average rainfall of 25mm/y and evaporation capacity of 1500mm/y. The vegetation is very spare here with strong aeolian action. So the denudation and aeolian transportation is very intense in eastern Tianshan. The timing of formation of this superarid climate is very important to the research of the relationship between plateau uplift and climate change. Jarosite is a widespread secondary mineral in oxidization zones of sulfide metal deposits in eastern Tianshan. There is considerable amount of potassium containing in the crystal of jarosite,so it is suitable to K-Ar(⁴⁰Ar/³⁹Ar)geochronology. The K-Ar data obtained from 7 samples indicate three age stages:11Ma,56～66Ma and 113～193Ma. Considering the contaminations of primary minerals(such as,Illite,Microcline,Albite and Quartz),the age of formation of jarosite in eastern Tianshan can be determined at～11Ma,which indicates the climate change from arid-semiarid to superarid in eastern Tianshan. It is consistent with the strengthening of Asian north-westerly winter monsoon and the records of large scale aeolian sediments. It also accords with the time of uplift and lateral expansion of Tibetan plateau along its northern and northeastern margins. The age of jarosite's formation in eastern Tianshan supports the climate-model that simulates the atmospheric circulation change caused by the uplift of 1～2km and lateral extension of Tibetan plateau.

STUDY ON THE SEISMOGENIC TECTONIC OF THE M_S 5.0 EARTHQUAKE IN WENXIAN,GANSU ON JUNE 21,2006

DAI Wei, ZHANG Hui, FENG Jian-gang, YAN Wu-jian

2009, 31(3):  424-432.  DOI: 10.3969/j.issn.0253-4967.2009.03.005

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No moderate and strong earthquake occurred for many years in Wenxian since the M8.0 great earthquake occurring in 1879 A.D. The June 21,2006 Wenxian earthquake with M5.0 occurred in an area where the tectonic setting is complex. Seismic activity level in Wenxian would enhance after the occurrence of this earthquake(M5.0). Since the earthquake did not produce surface rupture zone,it is very difficulty to study the seismogenic fault. However,we can still study the seismogenic fault based on geological map(1∶200 000),remote sensing interpretation,inversion of focal mechanism and seismic sequence precise location method. In order to determine the future seismic risk of the region,the paper intends to analyze the earthquake causative structure by jointly using the remote sensing interpretation,various methods of inversion of focal mechanism,and double-difference earthquake location algorithm. The geological map(1:200 000)shows there are many faults in this area,and the interpretation of remote sensing reveals that only one fault named Shifang-Linjing Fault is active. Focal mechanisms derived from the two methods show that the earthquake is of left-lateral strike-slip and thrust,and the principal compressive stress is in the direction of N60°E. The results of double-difference earthquake locations also support this result. The distribution of aftershocks is related to the thrust faulting. Results of combined analyses show that the Shifang-Linjiang Fault is the seismogenic fault of this earthquake,and the direction of the principal compressive stress is N60°E.

ANALYSIS OF IMPACT OF SOURCE REGION STRUCTURE ON SEISMOLOGY PARAMETER SCAN RESULTS

CHEN Yu-wei, HUANG Xian-liang, WANG Xing-zhou, SHEN Xiao-qi, MIAO Peng, CHEN An-guo, HE Kang, LI Fa

2009, 31(3):  433-440.  DOI: 10.3969/j.issn.0253-4967.2009.03.006

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By taking medium-strong earthquakes of South China,North China and western China as the research objects,this paper selects 8 kinds of seismology indexes with clear physical meaning and strong independence to carry out spatial scans of the parallel slip,vertical slip and oblique slip along the fault strike,respectively. Based on the size of correlation coefficients between scanning curve and source region curve,we analyze quantitatively the difference of scan results of different slip modes and study the impact of fault strike in different tectonic divisions on seismology parameters scanning results and variation rules. The results show that not only the change of spatial parameters has great influence on the seismological parameters scan,but also the fault strike in source region. This paper presents the optimum condition parameters with least influence space scope in scanning for different magnitude seismology indexes and analyzes the possible influence of fault strike on scanning results of seismology parameters.

THE SEGMENTAL CHARACTERISTICS OF GEOMETRICAL STRUCTURE OF THE EAST KUNLUN ACTIVE

LI Chen-xia, XU Xi-wei, WEN Xue-ze, ZHENG Rong-zhang, CHEN Gui-hua

2009, 31(3):  441-458.  DOI: 10.3969/j.issn.0253-4967.2009.03.007

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The paper carries out geometric segmentation of the eastern segment of East Kunlun Active Fault(Maqin-Maqu segment)based on the interpretation of ETM and QuickBird satellite images and using segmental signs of strike-slip fault,such as geometric and tectonic discontinuities in combination of geomorphic features and fault zone materials. In this study,we divide the Kunlun Active Fault(Maqin-Maqu segment)into eight segments,geometrically,namely,Dongqinggou,Dawutan,Kendingna,Xikehe,Tangdi,Maqu,Moxi and Luocha. Faults in the former seven segments are developed en echelon,of which,that in the Tangdi and Maqu segments are of right-stepping en echelon,and the rest are of left-stepping. The space between steps is small and well-connected. Beside the stepover,the segmentation indicators also include the bend of fault strike and the intersection of fault with others. Luocha segment is divided mainly by the strike bend. The east Kunlun Fault intersects with the Awancang Fault and Xikehe-Maqu Fault at the south side of Mohatang,which is taken as an indicator of segmentation of the Xikehe segment. The extensive landform and evidence of paleo-seismic rupture indicate that the Maqin-Maqu segment has experienced numerous movements. The fault splays out from northwest to southeast,which has good correlation with the slip rate gradients along the Eastern Kunlun Fault.

GEOMORPHOLOGIC CHARACTER AND QUATERNARY ACTIVITY OF THE NORTH OF YEMAHE FAULT IN SUBEI

ZHAO Peng, MIN Wei, JIAO De-cheng, SUN Zong-shi, HUANG Tuo

2009, 31(3):  459-469.  DOI: 10.3969/j.issn.0253-4967.2009.03.008

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The slip rate decreased at Subei,Shibaocheng and Shulehe regions on the eastern segment of Altyn Fault,the regions called as "singularity points". Subei is one of "singularity points" on the eastern segment of Altyn Fault,and the north of Yemahe Fault in the northeast of Subei is the fault we study in this paper. The fault is located in the northeast of Yemahe Basin. It starts at Erdaogou gully in the east and ends at Niujuan gully,extending along the Yema mountain front and parallel to the Altyn Fault in the direction of NEE on the whole. It separates Sinian from Quaternary gravel layer. There are plenty of left-lateral slip-strike and thrusting geomorphologic phenomena and exposed stratigraphic sections on the sides of gullies. Ridges and gullies are dislocated synchronously.Through more than one month investigation,we obtained the distribution and the geological and geomorphologic characteristics of the fault,measured a series of left-lateral slip gullies,ridges and thrust scarps and got the relevant data. Some samples are also collected. The left-lateral slip of gullies is distributed from 1.3m to 175m,and the height of thrust scarps is from 0.95m to 8.53m. The horizontal averaged slip rate of the fault is calculated to be 1.27?0.18mm/a,and the averaged thrusting rate is 0.4?0.07mm/a. This fault,together with the Danghenanshan thrust fault at its south,resolved part of the movement components of the eastern segment of Altyn Fault.

FAULT ACTIVITY ON THE HEPU BASIN SECTION OF THE HEPU-BEILIU FAULT

WANG Ming-ming, ZHOU Ben-gang, JI Feng-ju, CHEN Xian-cheng, CHEN Guo-guang

2009, 31(3):  470-487.  DOI: 10.3969/j.issn.0253-4967.2009.03.009

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Hepu-Beiliu Fault starts from Beibuwan sea area in the southwest,extends northeastwards continually though Hepu,Bobai. The total length of the fault exceeds 400 kilometers and the general strike of the fault is 40°～60°. The Hepu-Beiliu Fault comprises two branches-the east branch and the west branch. The west branch stretches from the southwest of the Hepu Basin lying in the lower reaches of the Nanliu River towards the northeast. This paper discusses the activity of the fault segment in the Hepu Basin in the west branch of Hepu-Beiliu Fault from the following three aspects. Firstly,in view of the geological topography,fault-scarps develop widely in the Hepu Basin segment of the west branch and the linear feature of the scarp distribution is notable; Secondly,some exact locations that the fault crosses are investigated by high-resolution seismic reflection profiling; Finally,in order to evaluate the activity and their times of the Hepu Basin segment of the Hepu-Beiliu Fault,borehole drilling is carried out to find out the dislocated stratum of the fault and take samples for laboratory dating to define the latest activity time of the fault. Based on the fault chronology results,the latest active era of this segment(the Hepu Basin segment of the Hepu-Beiliu Fault)is concluded in the late era of the lower Pleistocene. The fault slip displacement is about 10 meters. This fault is covered by the strata of the middle to upper of mid-Pleistocene,which means that the activity level of this segment became lower,or it has been inactive since the late eva of mid-Pleistocene.

FAULT ACTIVITY AND DELINEATION OF THE POTENTIAL SEISMIC SOURCES IN HUNAN

XIAO He-ping

2009, 31(3):  488-500.  DOI: 10.3969/j.issn.0253-4967.2009.03.010

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Located in the south China fold system,the eastern Hunan area has experienced several tectonic movements,which resulted in wide-spread distribution of folds accompanied by a series of NNE-NE trending faults,and some rift basins were developed along these faults. During the neotectonic movement,the crustal movement was dominated by large-scale and overall slow uplift with weak differential tectonic movement. However,this area has experienced a number of strong earthquakes,which are supposed to be related to the fault activities in the mid-Quaternary. Based on the collection and analyses of previous results of research in this area and its neighborhood,in this study,we carried out field geological and geomorphologic investigation to the southeastern segment of Changde-Yiyang-Changsha Fault,the northeastern segment of the Xiangtan-Shaodong Fault,and the Yongzhou-Hengyang Fault. Comprehensive analysis was made on the activity of these faults during the early Pleistocene epoch based on the two basic principles of "earthquake recurrence" and "structural analogy". Based on the geological,seismic and geophysical data of specific sites,it is concluded that these fault zones not only put up the evidence of mid Pleistocene activities,but have potential risk of moderate earthquakes in the areas around the fault zones. Considering the needs for social and economic development and other factors,the Xiangtan-Xiangxiang,Shaodong,Hengshan-Hengyang,and Yongzhou areas are regarded as new potential source regions.

APPLICATION OF WAVELET MULTI-SCALE ENTROPY TO CROSS-FAULT DEFORMATION DATA IN XINJIANG

LIU Guan-zhong, WANG Jian-jun, WANG Zai-hua, JIANG Jing-xiang, XIE Zhou-min, TAN Qiao

2009, 31(3):  501-514.  DOI: 10.3969/j.issn.0253-4967.2009.03.011

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Information extraction and analysis about cross-fault deformation is one of the important contents in earthquake research. Based on the theory of wavelet analysis and information entropy,the wavelet multi-scale entropy that describes the ordering degree in local data has been proposed in this paper. We studied the wavelet multi-scale entropy variation characteristics before strong earthquakes and the relationship between decreasing entropy anomaly and the three elements of earthquake by using the cross-fault fixed deformation data from Tianshan area in Xinjiang. The results indicate that:the amount of information of high frequency component is more than that of low frequency in cross-fault deformation rate,and a decreasing entropy anomaly appears before most of strong earthquakes. Furthermore,the logarithm of cumulative decreasing entropy is obviously linear with magnitude and the time from the beginning of anomaly to the occurrence of earthquake. If the magnitude is larger,the time from the beginning of anomaly to earthquake will be longer,and the cumulative decreasing entropy will be larger. Finally,the association is obvious between the integral decreasing entropy of multiple stations and large range crustal movement and the seismic active period.

EFFECT OF EXTRACTION OF GEOTHERMAL RESOURCES ON UNDERGROUND FLUID BEHAVIOR OF LIAOGU-1 WELL AND COUNTERMEASURE AGAINST IT

WANG Hua, WANG Wei, LI Yue-qiang, CHEN Qi-feng, WEI Ru-qing, ZHAO Jie-feng, FENG En-guo, CUI Na

2009, 31(3):  515-525.  DOI: 10.3969/j.issn.0253-4967.2009.03.012

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In this paper,hydrogeological condition of Liaogu-1 well was introduced; the present condition of extraction of geothermal resources around Liaocheng seism-hydrochemistry station was researched comprehensively. The effect of the extraction of geothermal resources on underground fluid observation and behaviors were analyzed basing on the research. It is believed that the extraction of geothermal resources in the well area resulted in the dry-up of Liaogu-1 well and the emergence of abnormal behaviors in various measurements. The extraction of karst water in carbonate rock around Liaogu-1 well affected the underground fluid observation and behaviors,the disturbance became more serious especially in winter when groundwater was mined for heating. In this paper,for the sake of removing or reducing the effect,the artificial self-flow was carried out by transformation of wellhead equipment. As a result,obvervation items were insured,obvervation condition of part of items was improved,the dynamic data of many obvervation items was continuable,only few items were affected seriously,and actual effect was obtained. But the essential way out is to protect the observation system and stop extraction of geothermal resources in same stratum.

ANALYSIS ON EFFECT AND CAUSE OF WATER CHEMISTRY BEHAVIOR IN WANG-3 AND WANG-4 WELLS DUE TO GEOTHERMAL EXPLOITATION

LIU Xue-ling, MA Jian-ying, LI Yi-bing

2009, 31(3):  526-535.  DOI: 10.3969/j.issn.0253-4967.2009.03.013

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Wang-3 and Wang-4 wells are two important wells for water chemistry observation in the Capital region. Whether or not the geothermal mining in Jingjinxincheng has influence to the two wells is of great significance to seismic regime monitoring. In this paper,based on the correlatability analysis of sharp pressure drop and water radon and water mercury changes caused by geothermal exploitation in Wang-3 and Wang-4 wells after July 2004 in Jingjinxincheng,we find that geothermal exploitation is the root cause of affecting earthquake observation in Wang-3 and Wang-4 wells despite different horizons and depths of geothermal aquifer and earthquake observation. Then,the author analyses the factors that influence the water chemistry behavior in Wang-3 and Wang-4 wells due to geothermal mining from the aspects of geological structure,development of Karst fissure,under-ground hydrodynamic condition,heat-dynamical condition,physical-chemistry equilibrium of underground water,and so on. Furthermore,the author puts forward some suggestions about site selection and construction of water chemistry observation well in geothermal anomaly area.

PRELIMINARY STUDY ON THE SEISMOTECTONICS OF YAO'AN & DAYAO MODERATE STONG EARTHQUAKE AREA

ZHANG Jian-guo, LIU Li-fang, LI Xi, XIE Ying-qing

2009, 31(3):  536-543.  DOI: 10.3969/j.issn.0253-4967.2009.03.014

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Analyses based on investigation of the seismic intensity and digital seismic data by mobile observation on-site from the Yao'an M6.0 Earthquake that occurred on 9th July 2009 in Yao'an county,Yunnan Province,and on the spatial distribution of earthquake sequences,focal mechanisms,and intensity distribution of other three earthquakes that occurred since 2000 in the same area with the similar magnitude,show that there are obviously different characteristics in earthquake focal depth,direction of the long axis of isoseismal lines,major trend of sequence spatial distribution,and so on of the four earthquakes. Comprehensive analyses combined with data from petroleum seismic exploration show that the regional seismotectonic setting is very complicated,featured by seismotectonics interweaved with different strikes and faulted structures coupling at different depths in Yao'an area.

A SIMPLE APPROACH FOR PREHEAT TEMPERATURE DETERMINATION IN FINE-GRAINED QUARTZ OPTICALLY STIMULATED LUMINESCENCE DATING

KANG Shu-gang, LU Yan-chou, WANG Xu-long, DU Jin-hua

2009, 31(3):  544-550.  DOI: 10.3969/j.issn.0253-4967.2009.03.015

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Equivalent dose(De)preheat plateau test is an often used approach to determine an appropriate preheat temperature in optically stimulated luminescence(OSL)dating. The preheat temperature chosen in OSL dating should be in the plateau region. When the preheat time is fixed as 10s,the De preheat plateau regions are 250～280℃ and 180～260℃ for regeneration dose and test dose respectively for fine-grained quartz in Chinese loess,no matter using single-aliquot regenerative-dose(SAR)protocol or sensitivity change corrected multiple-aliquot regenerative-dose(SMAR)protocol. After reanalyzing the De preheat plateau data derived by SMAR protocol,variation of the ratio of natural OSL intensity to regenerated dose aliquot OSL intensity(N/R)with preheat temperature changes in the similar way with the plot of De as a function of preheat temperature. We suggest that plot of N/R as a function of preheat temperature can be the substitute of De preheat plateau test. This gives us a simple and time-saving approach to determine the preheat temperature in fine-grained quartz OSL dating.

CONTINUOUS ELECTROMAGNETIC MEASUREMENT AT STATIONARY STATIONS AND ITS APPLICATION TO EARTHQUAKE PREDICTION RESEARCH

TIAN Shan, TANG Ji, WANG Jian-guo, XU Xue-gong, CUI Xiao-feng, ZHANG Ming-dong, CAO Jing-quan

2009, 31(3):  551-558.  DOI: 10.3969/j.issn.0253-4967.2009.03.016

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Based on the synchronized observation data of 1s sampling rate Network MT(N-MT)system with FHDZ-M15 geo-magnetometer installed at Jinghai seismic observatory in the "Tenth Five-Year Program" period,we carried out the MT measurement at a stationary station. Robust technology was employed in data processing to the data recorded at Jinghai observatory from January to June,2008. The tensor impedances were obtained. The temporal abnormal change of 18 apparent resistivity and impedance phases of same-period in the range of periods of 6～600s was analyzed. The results show there exist changes in some periods of apparent resistivity and impedance phases before the M_L 4.2 Lulong earthquake on March 17,2008. In this study,the period of data used corresponds to the depth of 5～ 50km,a range of focal depth of North China. The result indicates the change of electrical conductivity of the strata in the source area before and after the earthquake. The MT method can reflect the electrical conductivity changes at the source area more directly than the existing geoelectric observation methods,and it has bigger advantage for deeper exploration.

A REVIEW ON DECAY AND GENERATION OF AFTERSHOCK ACTIVITY

SONG Jin, JIANG Hai-kun

2009, 31(3):  559-571.  DOI: 10.3969/j.issn.0253-4967.2009.03.017

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Focusing on decay and generation of the aftershock activity,the latest theoretical advancements and applications on the modified Omori law,the ETAS model and the BASS model have been introduced in this paper. Up to now,the modified Omori law is the best formula for fitting the temporal decay of aftershock activity,which has been used to describe the decay characteristics of aftershock sequences quantitatively. Essentially,the modified Omori law is a typical statistical model on observing phenomena,but it has been used widely in practice owing to its less parameters,simple calculation,and higher capability of describing the general features of sequence decay. ETAS model,which takes into account the generation of the high order aftershocks with statistical self-similar characteristics,is a physical expansion of the modified Omori law,and the generation intensity of high order aftershocks is concerned to be related to the magnitude of the father earthquake. Since considering the problems of high order aftershock generation,ETAS model not only has a large improvement in study field of aftershock sequences,but also has many other applications,such as detection of relative quiescence,removing of the cluster aftershock activity,assessment of background seismicity,detection of seismic activity triggered by external factors and so on. BASS model follows the modified Bath's law,while the ETAS model follows the similar rate with the magnitude of the father earthquake,this is the largest difference between ETAS model and BASS model. So,the BASS model is a completely self-similar theoretical model compared with the ETAS,but only few papers concerning its application.