Table of Content

11 March 2009, Volume 31 Issue 2

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Application of new techniques

THE PLATE SUBDUCTION AND STRESS STATE IN THE PAMIR-HINDU KUSH REGION

SUN Wen-bin, HE Yue-shi, CHANG Zheng, QI Xiao-yan

2009, 31(2):  207-217.  DOI: 10.3969/j.issn.0253-4967.2009.02.001

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In this paper,the collision configuration between Indian plate and Eurasian plate was studied in detail and the focal mechanism solutions of the earthquakes were analyzed by using the earthquake catalogues from 1973 to 2006 provided by NEIC and focal mechanism solutions from 1978 to 2005 provided by Harvard University.The results indicate that:Eurasian plate was underthrust southwards with a dip of 50?,and the maximum focal depth is 364km;Indian plate collided with Eurasian plate by means of interlayer intercalation.The collision was strong among the Pamir knot,where the seismic activities were enhanced significantly.The focal profile shows a "V-shape" distribution;on the sides of the Pamir knot,the seismic activities decreased apparently along with the decreasing subduction force of the Indian plate.The focal profile indicates that the profile configuration of the northward-subduction of the Indian plate disappeared gradually and the profile configuration of the southeastward-subduction of the Eurasian plate is more perspicuous.The analysis on the distribution pattern of the focal profile suggests that the Indian plate did not penetrate the Eurasian plate.The repeated multi-period and imbricate distribution of earthquake may be the reflection of the process of northward-subduction,detachment,and then re-subduction and re-detachment of the Indian plate.As a result of strong collision and extrusion between Indian plate and Eurasian plate,Pamir-Hindukush region is under a tectonic stress state of near-NS compression.The number of reverse faults accounts for about 70%of the total,the normal faults account for about 11%,and the strike-slip faults,about 19%.The predominant orientation of P axis indicates that the principal compressive stress is oriented near-NS,the dip is near-horizontal,inclining from south to north;and the dip of T axis is near-vertical,similar to the dip of subduction zone.Characteristics of stress field in Pamir-Hindukush show that the active northward-extrusion of Indian plate is the main dynamics of the regional stress field,and the Eurasian plate which dips southward is in a state of passive extrusion.

Brief Report

A NEW MECHANISM TO TRIGGER EARTHQUAKE:THE COUPLING BETWEEN FRACTURE AND THE CRITICAL SINGULARITIES OF WATER IN THE LITHOSPHERE CAUSES THE EARTHQUAKE

HU Bao-qun, LÜ Gu-xian, WANG Fang-zheng, SUN Zhan-xue, LI Man-gen, BAI Li-hong

2009, 31(2):  218-225.  DOI: 10.3969/j.issn.0253-4967.2009.02.002

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Taking the case of the iso-pressure heat capacity,the paper has studied the critical singularities of water and its appearing condition in the lithosphere,and discussed the possibility of triggering earthquakes by the coupling of the critical singularities and fractures.There are first-order and second-order phase transitions of water in the lithosphere.When the phase transitions appear,the physic-chemical characteristics of water will also change,and the change will be huge at the critical point of water,namely the critical singularity.Because of the critical singularity of water,some physic-chemical characteristics,such as the heat capacity and the coefficients of thermal expansion and compression,will approach infinity.According to the Mie-Grüneisen formula(∂P/∂T)^V=γρC^V),the infinity of the heat capacity of water will cause the thermal-pressure to become the infinity too.Instantaneously,the pressure will sharply increase and trigger the earthquake.But the temperature is related to pressure according to the geothermal curve of the lithosphere.Calculated with the normal geothermal gradients(15～35℃/km)and the geopressure gradients(0.025～0.03GPa/km),the depths of critical temperature and critical pressure of water are respectively 24～10km and 0.88～0.73km.It means there are no places where temperature and pressure can simultaneously approach the critical values of water in the lithosphere if there are no fractures.In such case,the critical singularity cannot appear.The fractures can cause the pressure to decrease to the critical pressure of water,so the temperature and pressure will approach to the critical values of water in some place in the lithosphere.The condition of appearing the critical singularity of water is the temperature and pressure simultaneously approaching the critical values of water.The result of the research has proposed that the coupling between the critical singularities and fracture is essential to trigger earthquake.

INVESTIGATION AND ANALYSIS TO CO-SEIMIC BLOWOUT IN CHAGAN WELL

CHE Yong-tai, YU Jin-zi, LIU Cheng-long, WAN Yong-fang, LUO Sheng-qin, HE Yong-qing, XIAO Zheng-dong

2009, 31(2):  226-232.  DOI: 10.3969/j.issn.0253-4967.2009.02.003

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Violent blowouts occurred in Chagan Well when the M_S 8.7 Sumatra earthquake happened on Dec.26,2004,with the eruptive fountain up to 60m high.The result of investigation and analysis of Chagan well indicates that blowout occurred in the condition of special hydrogeology.The water of monitoring layer was rich of CO₂.When the aquifer of monitoring was disturbed by the earthquake wave,a large number of absorbed gases were released.On the other hand,free bubble was broken by the earthquake wave and the groundwater was gasified,leading to the rapid increase of the pore pressure.

EVIDENCE OF THE DONGBEIWANG-XIAOTANGSHAN FAULT IN BEIJING

HE Zhong-tai, MA Bao-qi, LU Hai-feng, WANG Jin-yan

2009, 31(2):  233-246.  DOI: 10.3969/j.issn.0253-4967.2009.02.004

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Lots of different ideas stay on whether the Dongbeiwang-Xiaotangshan Fault in the northwest of Beijing exists or how it displays and acts.This paper analyzes the present seismic prospecting data and drill logs from exploration of active faults in Beijing urban areas,and reaches conclusion that the Dongbeiwang-Xiaotangshan Fault does exist as a subsurface fault and it is 40km long,trending NNE.Divided by the Nankou-Sunhe Fault,we name its northeast segment as the Xiaotangshan Fault and the southwest segment as the Dongbeiwang Fault.The Xiaotangshan Fault is active in early Pleistocene but not in middle Pleistocene.The Dongbeiwang Fault is active in the end of mid-Pleistocene but not in late Pleistocene.

DISCOVERY OF SURFACE RUPTURE ZONE ON THE SOUTH OF HELISHAN IN GAOTAI,GANSU PROVINCE

ZHENG Wen-jun, ZHANG Pei-zhen, YUAN Dao-yang, GE Wei-peng, LIU Jian-hui

2009, 31(2):  247-255.  DOI: 10.3969/j.issn.0253-4967.2009.02.005

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According to the new investigation in the northern Hexi corridor,remains of two surface rupture zones are discovered on the southern margin fault of Helishan.One rupture has the length of about 7km and the other about 10km.The two surface rupture zones might be produced by the nearest earthquake event.On the surface rupture zones,there are continuous scarp and free face caused by rupture.The scarp is about 1～1.5m high and on some site is up to 2m nearly.According to the OSL result,the nearest T₁ terrace and higher flood plain forming 3000a BP are dislocated by the fault.All above reveal that the rupture age should be later than that of T₁ terrace.But in the historical data and earthquake catalogue,we didn't find related information about the fault and surface rupture in this area.The 180 AD M 8 Biaoshi earthquake and 756 AD M 7 Zhangye-Jiuquan earthquake are documented in historical data.It is inferred by textual research that the two earthquakes are related with the northern marginal fault of Yumushan in the south of basin.Due to lack of reliable evidence,there still exist many arguments on this inferred conclusion.So we hold that the two surface rupture zones were produced by one of the two large earthquakes or another unrecorded historical event.The research on the activity and surface rupture of this fault can offer valuable information for the tectonic study and strong earthquake risk estimate of this region in the future.

STUDY ON HOLOCENE ACTIVITY OF THE SOUTH SEGMENT OF THE EASTERN PIEDMONT FAULT OF HELAN MOUNTAINS BETWEEN TAOMENGOU AND YUSHUGOU

DU-Peng, CHAI Chi-zhang, LIAO Yu-hua, SONG Fang-min, MENG Guang-kui, LEI Qi-yun, WANG Yin

2009, 31(2):  256-264.  DOI: 10.3969/j.issn.0253-4967.2009.02.006

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The eastern piedmont fault of Helanshan Mountains is an important tectonic controlling the west boundary of Yinchuan graben.The south segment of the fault locates right in the west of Yinchuan city,which has a length of about 13.2km,strikes NNE-NE and dips south-east at an angle of 50°～80°.The main part of the fault lies between the Ordovician and Quaternary systems,forming the borderline between the hills and diluvium.Parts of the segment of the fault appear in alluvial fans and are displayed as geomorphic scarps.The paper selects the region on the two banks of Dashitou channel to excavate two trenches along the fault based on 1:10,000 geological mapping of the fault area.The result reveals three events since 14ka BP with the ages of 13.8,7.9 and 3.0ka BP and the recurrence intervals of 6 and 5ka,respectively.

PALEOEARTHQUAKE STUDIES ALONG NALINLAKA FAULT OF LATE PLEISTOCENE IN LHASA,TIBET

LIU Jing, SHEN Xu-hui, XU Yue-ren, SHEN Jun-feng, JING Feng, HONG Shun-ying

2009, 31(2):  265-275.  DOI: 10.3969/j.issn.0253-4967.2009.02.007

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As the most important fault of Late Pleistocene in the Lhasa area,the Nalinlaka Fault is a left-lateral thrust fault,striking NWW,dipping SSW with a high dip angle,and extending over 33km.According to the studies on the latest strata on the Nalinlaka Fault zone,this fault zone has been obviously active since Late Pleistocene and the movement left behind some geomorphologic phenomena on the earth's surface,especially at the sites of the gully west of Cijiaolin and around Xiecun village.For example,some rivers,ridges and terraces are dislocated,forming beheaded gullies,fault escarps and so on.The horizontal displacements since Late Pleistocene at the above two places are 54～87m and 20～67m,respectively.Based on the studies on the 4 trenches along the fault using progressive constraining method,we conclude that there might have occurred 5 paleoearthquake events along the Nalinlaka Fault since 70ka BP,the ages of each paleoearthquake are 8.53,54.40,<41.23,21.96,and 9.86 ka BP,and the average recurrence interval is 14.67ka.Because of the limits of trenches and earthquake events exposed by each trench,no single trench revealed completely all the 5 events.So,there may be some errors in determining the upper and lower limits of some events in this article.

论文

EFFECT OF SHEAR LOADING PERTURBATION ON FRICTIONAL BEHAVIOR:AN EXPERIMENTAL STUDY

HUANG Yuan-min, MA Sheng-li, MIAO A-li, HE Yong-nian

2009, 31(2):  276-286.  DOI: 10.3969/j.issn.0253-4967.2009.02.008

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We have performed a series of frictional experiments using a servo-controlled biaxial loading machine with three granodiorite block direct shear configuration.In the experiments,a small-amplitude sine wave of displacement is modulated to shear loading to study the effects of shear stress perturbation on stick-slip instability.The main results are as follows.Under constant normal stress and constant loading point velocity in shear direction,the sample shows regular stick-slip behavior.After the displacement perturbation is modulated to shear loading,the correlation between the timing of stick-slip and the perturbation increases as the perturbation amplitude increases.Stress drop and interval time of stick-slip events also tend to be scattered,and the critical amplitude for producing significant impact is around 0.05MPa.The tendency that the stress drop and interval time of stick-slip events are scattered with increasing perturbation amplitude is more obvious at higher normal stress,and the correlation between the timing of stick-slip and the perturbation also increases with increasing normal stress at the same perturbation amplitude.The effect of perturbation period on friction is not evident.The results imply that the change in Coulomb shear stress caused by strong earthquake may obviously change not only the occurrence time of earthquakes but also the earthquake magnitude on nearby faults.

APPLICATION OF STATISTICAL FORECASTING MODEL TO THE PREDICTION OF THE THREE GORGES RESERVOIR INDUCED SEISMICITY

WANG Qiu-liang, YAO Yun-sheng, XIA Jin-wu, LI Jing-gang, WANG Dun

2009, 31(2):  287-294.  DOI: 10.3969/j.issn.0253-4967.2009.02.009

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Based on field investigation in the reservoir head area of the Yangtze Three Gorges,combining with its seismogeological background and past research achievements,the reservoir head area is divided into 31 predictive units,and together with 8 impact factors,the possibility and magnitude of reservoir induced seismicity(RIS)are predicted using statistical forecasting model.The results show as follows:(1)it is quite possible that M_L=3.0～4.5 earthquakes will be triggered along the Jiuwanxi-Lukouzi Fault and Xiannvshan Fault in the reservoir area;(2)According to the analysis of earthquakes at home and abroad,the RIS takes place mainly in carbonatite and igneous rocks,and concentrates in karst developing segment,yet it is little possible that earthquake happens in clastic rock area.From the predictive results,it is possible to trigger M_L 4.5～6.0 earthquake in two places,the limestone area of southern Badong and the limestone area on the Gaoqiao Fault;(3)Around the Gaoqiao Fault,tectonic reservoir-induced earthquake is quite likely to occur.Geological investigation shows that the M_L 5.1 Longhuiguan earthquake in 1979 was possibly related to the Gaoqiao Fault which had a certain activity during the early period of reservoir impounding.The maximum magnitude of earthquake happening around the Gaoqiao Fault reaches to M3.3.The bigger earthquakes might be induced near the reservoir segment of Gaoqiao Fault along with the water storing to the design level.

Brief Report

RESEARCH ON THE HISTORICAL DATA OF THE 1585 AD CHAOXIAN EARTHQUAKE AND ITS SEISMOGENIC STRUCTURE

ZHAI Hong-tao, DENG Zhi-hui, ZHOU Ben-gang, LI Guang, ZHENG Ying-ping

2009, 31(2):  295-304.  DOI: 10.3969/j.issn.0253-4967.2009.02.010

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In 1585,an earthquake with M_S5³/4 happened in the south of Chaoxian of Anhui Province,and the parameters of this earthquake listed in earthquake catalogues of varied versions are different.According to the detail textual research of the historical earthquake records,the epicenter location of this earthquake is further confirmed by means of field seismo-geological investigation in the Chaohu-Tongling region of the western Changjiang valley.Shallow seismic prospecting and drilling methods are applied to study the buried fault,the possibility of existence of seismogenic fault and fault activity in the western Changjiang valley area are analyzed in depth,and the causative tectonic background of the 1585 M_S5³/4 south Chaoxian earthquake is studied.The result of this study indicates that the Yanjiaqiao-Fengshahu Fault,which was active in early Pleistocene to mid-Pleistocene,is possibly the causative structure of this earthquake.To identify the seismogenic structure of the 1585 south Chaoxian earthquake is helpful to deeply know the tectonic background of the moderate and small earthquake activities in eastern China.

ELECTROMAGNETIC EFFECT ASSOCIATED WITH AFTERSHOCK OF THE M_S6.4 NING'ER EARTHQUAKE

XU Guang-jing, TANG Ji, CHEN Xiao-bin, XIAO Qi-bin, WANG Ji-jun, CAI Jun-tao, WANG Li-feng, ZHAN Yan, WANG Xiao

2009, 31(2):  305-312.  DOI: 10.3969/j.issn.0253-4967.2009.02.011

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The EM measurement of earthquake monitoring for M_S 6.4 Ning'er aftershock series has been done at a continuous observation site after the earthquake on June 3,2007.The data was observed for 14 days.Very strong coseismic signals of aftershocks were found in the magnetic and electric fields' time series data.Electric and magnetic auto power spectrums have been obtained by using FFT in the bihourly data.The spectrum variations for the same frequency were compared.It was found that the peak of all components bounced before and after earthquakes of M_S≥3.0.This phenomenon may be corresponding to the coseismic signal and the electromagnetic precursor before and after the earthquake.We also discussed the mechanism in the paper and the seismo-dynamo effect seems to be a plausible mechanism.

STUDY ON THE CRUSTAL THICKNESS BENEATH STATIONS OF SEISMIC NETWORK IN SHAANXI PROVINCE BY TELESEISMIC RECEIVER FUNCTION

LIU Chun, CHONG Jia-jun, NI Si-dao, LI Shao-rui

2009, 31(2):  313-320.  DOI: 10.3969/j.issn.0253-4967.2009.02.012

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In this paper,we calculate receiver functions of body wave under the 14 stations in Shaanxi Province from 3-component digital waveform data of teleseismic earthquake events and obtain the thickness and Poisson ratio in crust of this area through H-kappa stacking.Through analysing the characteristics of crustal structure in Shaanxi Province,we discuss the relationship between seismic activity,crustal structure and geological structure in Shaanxi Province.The results show that(1)Crustal thickness in western Shaanxi is thicker than that in the east.Crustal thickness in the south and north of Shaanxi(≥40km)is larger than that in Weihe Basin,middle Shaanxi(about 34～40km).Among 14 stations,the crust beneath Huayin station is the thinnest(34km),which locates on the boundary between eastern Weihe Basin and Shanxi Province,and the biggest thickness(48km)appears beneath Longxian station at the northwestern end of Weihe Basin.(2)Poisson ratio in Shaanxi Province is about 0.24～0.29,which may be related to rock compositions.Poisson ratio in the north of Weihe Basin has higher values than those in the south.(3)There exist some relations between seismic activity and geological structure.The Weihe Basin with frequent earthquakes locates in a compound position of several tectonic systems.The Hanzhong Basin and Ankang Basin in the south of Shaanxi are controlled by several major faults,where the seismicity is relatively low.Seismic activity in northern Shaanxi is the lowest because of stable geological structure.Poisson ratio reflects material composition of earth interior.Our analysis suggests that seismic activity in the region with high Poisson ratio is higher than that with low Poisson ratio.

ANALYSIS AND SIMULATION OF SPATIAL DISTRIBUTION OF DISASTER BASED ON DISASTER REPORTS FROM DISCRETE DOTS AT EARTHQUAKE SITE

SHUAI Xiang-hua, HOU Jian-sheng, LIU Qin

2009, 31(2):  321-333.  DOI: 10.3969/j.issn.0253-4967.2009.02.013

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Earthquake always happens in an instantaneous and abrupt way,and the aftermath of an earthquake is difficult to be expected.The earthquake fieldwork teams are very difficult to arrive at the earthquake-stricken site and to provide the relevant information in 2 hours after an earthquake breaks out.We usually call this period of time as the "black-box" period of earthquake.The M_S 8.0 Wenchuan earthquake caused extremely high damage and wide influencing range,and how to quickly obtain the information on the disaster situation is of vital significance to earthquake emergency commanding and disaster mitigation.Actually,in this time section,people in the quake-affected area may gain some local disaster information,but how to collect,analyze and process this disaster information,and to provide it as reference information to the decision-makers for disaster mitigation and relief are the important research interests in emergency commanding.Therefore,the National Headquarters for Earthquake Disaster Mitigation has established the earthquake disaster short-message-service experimental platform which is based on the public service number 12322 for disaster mitigation to enable the interactive link between the handsets or other wireless terminals of the disaster reporting personnel at the earthquake-stricken area and the backstage headquarters,and to carry on corresponding processing of the information gained to further shorten the "black-box" period.The basic concept of the earthquake disaster short-message-service fast report platform is to define the handset or other wireless message terminal users as the disaster reporter,after an earthquake occurs,the earthquake disaster short-message-service central management platform sends out the downward invitation short message to collect earthquake disaster situation firstly,and upon receiving this short message,the disaster reporting personnel report the disaster situation of his/her own area to the earthquake disaster short-message-service central management platform in a preset format.After receiving the reports,the central management platform will make the analysis and spatial location on the national map,and carry on the algorithmic analysis of these spots to simulate the regional spatial distribution of the disaster.The disaster situation collection and analysis process on this platform is a dynamic change process with the disaster situation data collected,reflecting the earthquake disaster distribution information dynamically.The article introduces the interpolation algorithm and the technical realization in the simulation of disaster spatial distribution based on the reported messages of disaster situation from discrete spots on the earthquake disaster report platform.The discrete disaster situation spot is defined as Dot(x,y,z),in which x is the longitude of the discrete disaster situation spot,y is the latitude of the discrete disaster situation spot,and z is the attribute information of the discrete disaster situation spot.The value of z is 1,2,3 or 4 respectively,1 expresses no shaking felt or shaking felt slightly;2 expresses shake felt strongly,but no damage caused;3 expresses damage caused,but no casualties;4 expresses severe damage and casualties.Through analyzing the characteristics of discrete disaster situation spot information,and by contrasting among several interpolation algorithms,we finally adopted the method which combines GIS spatial analysis with Thiesen space interpolation algorithm to carry on the areal interpolation analysis for the discrete spot.The concrete algorithm steps are:(1)using Thiesen polygon algorithm to carry on the division and the interpolation of the sampling site,and to set up a polygon;(2)regarding the z value,the Z value of the interpolation point distributing in the Thiesen polygon region is equal to Z value of the sampling site in this region;(3)revising the outer boundary of GRID image.The interpolation calculation usually creates a GRID image with rectangle outer boundaries,which does not conform to the actual disaster distribution.So,this article uses the BUFFER analysis as the geographical space analysis method to determine the boundary of the calculating region;and(4)revising the internal boundaries.Different local disaster situation distributions exist in the Thiesen polygon,the partitioning of different disaster regions is usually not very smooth,so revision is made to the internal boundaries by means of re-sampling.This article uses the nearest neighborhood method to carry on the re-sampling analysis and computation.Based on the above method and model,we develop the experimental system by ARCGIS and WebSevice technology.The system was applied to the Wenchuan earthquake to a certain extent.The paper presents the analysis results of the data collected up to 24:00,May 12,2008,and the results tally basically with the actual disaster situation.The above model and system can make dynamic analysis and simulation with the change of the disaster information collecting points,and thus can promptly reflect and determine,to a certain extent,the rough distribution of earthquake disaster and provide the relatively accurate disaster distribution information for the earthquake emergency commanding and disaster mitigation.

OBSERVING COSEISMIC DEFORMATION OF THE GAIZE,XIZANG EARTHQUAKE WITH DIFFERENTIAL INTERFEROMETRIC SAR

ZHANG Gui-fang, SHAN Xin-jian, ZHANG Guo-hong

2009, 31(2):  334-340.  DOI: 10.3969/j.issn.0253-4967.2009.02.014

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There are two earthquakes in Gaize on Jan 9(M_S 6.9)and Jan 16,2008(M_S 6.0).The two earthquakes were selected as examples to obtain the co-seismic deformation field with the 2-pass differential interferometric processing method.The results show that the earthquake faults locate near the tip of the Yibuchaka-Riganpeicuo Fault,and both seismic faults are normal faults;The seismogenic fault of the main shock strikes about N30癊 and that of the aftershock strikes about N21癊;There is evidence of surface rupture along the mainshock's causative fault,but no surface rupture has been observed on the aftershock fault;The co-seismic deformation field is about 30km in length and 20km in width;The maximum displacement in LOS of the hanging wall of the main-shock fault is 39.2cm,and that of footwall is 11.2cm,the relative dislocation between them is 50.4cm;The displacement caused by the aftershock is 9.4cm(LOS).

THE DATA MANAGEMENT OF LARGE-SCALE SEISMIC ARRAY BASED ON SEISCOMP

WU Ming-shu, LIU Zhi, CHEN Jiu-hui

2009, 31(2):  341-348.  DOI: 10.3969/j.issn.0253-4967.2009.02.015

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With the establishment of China Seismic Array for Scientific Research,large-scale mobile seismic array observation projects have been carried out.One of the observation projects,named Dynamical Process of Active Block Boundary Belts and Strong Earthquake Prediction,consists of about 300 sets of broadband seismic instruments in Sichuan and Yunnan.And another seismic array for experimental survey equipped with about 250 sets of seismic instruments has been in operation in the capital area of China.As representative projects,an unprecedented urgent request was raised on the effective management and automatic processing for mobile digital seismic array data.The data acquired from mobile digital seismic instruments is stored in many scattered storage medium.For better storing,processing and use of the data,all the data should be archived in accordance with the requirements of a unified format.Seismic array data has unique characteristics of liquidity,density and relevance.It is necessary to ensure efficient management of many related parameters of array equipment.Ensuring an easy way to amend and change the observation data and pooling them to data center are also needed.Data management solutions to seismic network can not fully meet the actual needs.In this paper,SeisComp software which can be used for seismic array data management and preprocessing is introduced together with its data archive characteristic.A high efficient algorithm for seismic array data management is proposed based on SeisComP packages,which conforms data format conversion and parameter modification and realizes the automatic data archiving and pick-up.The method improves the efficiency of data management,and meanwhile,facilitates the data information distribution and waveform data sharing.

A REVIEW ON SITE CLASSIFICATION METHOD AND ITS APPLICABILITY IN EARTHQUAKE ENGINEERING

PENG Yan-ju, LÜ Yue-jun, HUANG Ya-hong, SHI Chun-hua, TANG Rong-yu

2009, 31(2):  349-362.  DOI: 10.3969/j.issn.0253-4967.2009.02.016

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Two kinds of site classification methods commonly used in earthquake engineering are analyzed in this paper.One is standard methods stipulated in seismic codes,and used to determine the site effects on seismic parameters for the seismic resistance of structures,the site classification methods and site indexes in seismic codes of China,United States,Europe and Japan are presented,and the problems about site index are discussed,such as the calculation method and depth of shear wave velocity,the choice of initial layer,the grade of overburden thickness,etc.Then some suggestions are put forward for the new generation of seismic code in China.The other kind of site classification methods is used to predict site effects on a large scale for a regional seismic hazard prediction.The popularly studied methods based on geology,topography and geomorphology are described in detail.The common character of this kind of methods is to find an easily obtained macro index,and to summarize the rules between the macro index and the site index in seismic codes(shear wave velocity in most cases),and then the regional site category zonation can be delineated.The response spectrum methods of ground motion are also presented here,such as RSS(Response Spectral Shape)and HVSR(Horizontal-Vertical Spectral Ratio),they can be used in areas with abundant ground motion records.Finally the advantage,limitation and applicable scope of these methods are discussed.

A DISCUSSION OF THE PREPARATION PROCESS OF THE M_S 8.1 WEST KUNLUN MOUNTAIN PASS EARTHQUAKE

CHEN Yu-hua, DONG Zhi-ping, CHENG Jian-wu, FENG Jian-gang

2009, 31(2):  363-371.  DOI: 10.3969/j.issn.0253-4967.2009.02.017

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Before the M_S 8.1 West Kunlun Mountain Pass earthquake,an orderly evolution of seismicity patterns was observed in the Qinghai-Tibet block:the evolution of seismic gaps showed a time span of several to decades of years and a space span of hundreds to thousands of kilometers,and that of seismic stripes had a time span of several years and a space span of thousands of kilometers.After 1990,the seismic precursory observation networks in Qinghai,Gansu,Sichuan,Xinjiang and Ningxia Provinces and autonomous regions recorded some typical far-field anomalies.These abnormal tendency changes roughly coincided with the formation time of seismogenic gaps and seismic stripes and were distributed in the Qilian Mountains tectonic zone,the East Kunlun tectonic belt,the West Qinling tectonic belt,the north-south tectonic belt and the Tianshan tectonic belt.The far-field anomalies and the spatial-temporal evolution of seismic gaps were complementary and correlated to each other.This article discusses the ordered and phased characteristics in the evolution of the above anomalies with the space-time preparation process of the M_S 8.1 earthquake.