Table of Content

21 December 2006, Volume 28 Issue 4

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Brief Report

EMPIRICAL RELATIONSHIPS BETWEEN MAGNITUDE AND RUPTURE LENGTH,AND RUPTURE AREA,FOR SEISMOGENIC ACTIVE FAULTS IN NORTH CHINA

LONG Feng, WEN Xue-ze, XU Xi-wei

2006, 28(4):  511-535. 

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Estimation of sizes of potential earthquakes is required in long-term seismic hazard assessment.Such estimation is usually related to a single active fault segment with specific scale,and can be carried out by using an empirical relationship between magnitude and rupture-scale of earthquake.This type of empirical relationships published already for China mainland is established on data of surface ruptures along seismogenic active faults in West China.While,the special active tectonic environment in the region of North China makes it impossible to establish the same type of empirical relationships that are suitable for the region by using the surface-rupture data.Therefore,for North China,we should make an effort to develop the empirical relationships between earthquake magnitude and(sub-surface)source rupture-scale.In the latest 40 years,4 major earthquakes of magnitudes ≥7.0,7 strong ones of magnitudes 6.0 to 6.9 and tens of moderate ones(including aftershock events)of magnitudes 5.0 to 5.9,occurred in North China.For a part of these earthquakes,data or distribution patterns of aftershock sequences with good or high precision locations are available,and for many of these earthquakes,studies on source rupture processes and parameters have been carried out.These make it possible to establish preliminarily the empirical relationships between magnitude and rupture-scale for North China.For this purpose,from data of earthquakes that occurred in North China since 1965,we systematically collected and compiled the relevant rupture-scale parameters obtained from methods of analyzing seismic wave spectrum,coseismic crustal deformation and aftershock distribution,or available from published researches,including rupture length L,downdip rupture width W,and rupture area A(A=L×W).We also re-determined the rupture-scale parameters for part of these earthquakes basing on aftershock distributions.In order to deal with uncertainties in the source rupture-scale parameters due to the use of various methods,and to take the main factors influencing the uncertainties into account,we broungt forward 8 criterions for determining the reliable parameters through further analyses and identification.With synthetic analyses basing on these criterions,we obtained reliable rupture-lengths of 34 earthquakes and reliable rupture-areas of 20 of the 34 earhtquakes.Focal mechanism data suggest that the absolute majority of the 34 ruptures are of strike-slip type.By using the least-square method,we further established two regression relationships between surface-wave magnitude M_S and rupture-length L,and between magnitude M_S and rupture-area A for seismogenic active faults.They are M_S=3.821+1.860lg(L)and M_S= 4.134+0.954lg(A),respectively.A comparative analysis with previous empirical relationships of the same type suggests that the two new empirical relationships developed in this research are suitable very well for estimation of sizes of potential earthquakes on seismogenic active strike-slip faults in North China and in the urban area of Beijing and its surroundings.

COMPREHENSIVE MULTI-LEVEL EXPLORATION OF BURIED ACTIVE FAULT:AN EXAMPLE OF YINCHUAN BURIED ACTIVE FAULT

CHAI Chi-zhang, MENG Guang-kui, DU Peng, WANG Yin, LIU Bao-jin, SHEN Wei-hua, LEI Qi-yun, LIAO Yu-hua, ZHAO Cheng-bin, FENG Shao-ying, ZHANG Xue-hui, XIE Xiao-feng

2006, 28(4):  536-546. 

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Yinchuan Basin is a graben-like downfaulted Cenozoic era basin located on the west edge of Ordos Massif.Its activity is violent and deposition is very thick.Yinchuan City is located in the middle of Yinchuan Basin.The seismic petroleum exploration shows that a buried active fault lies in the east of Yinchuan City,named as the Yinchuan buried fault,which strikes NNE and dips west,with a total length of more than 80km.Because the seismic petroleum exploration did not gain any explained signals at the depth ranging from 0 to 400m,so whether the Yinchuan buried fault is active or not in the late Quaternary and its exact surface projective location hasn't been known yet.It has been a “worry” in the urban planning and development of Yinchuan for a long time.Under the financial support of the national and local governments,we launched the project entitled “The prospecting of active fault and earthquake risk assessment in Yinchuan City”.In order to facilitate the exploration,we selected Xinqushao village in the southeast suburb of Yinchuan City to be the site for the integrated test exploration of the Yinchuan buried fault before the exploration,based on the information obtained from the seismic petroleum exploration.Considering that the thick Quaternary sediment in Yinchuan reaches to 1609m,and that the depositional environment is the Yellow River flood plain and the lateral change of lithology is complex,we adopted in the test exploration the train of thoughts of “inferring an unknown fact from a known fact,and from deep to shallow and directly to the top”.The experimentation has been developed step by step according the working order of multilevel seismic exploration→composite geological profile drilling→trenching.Along the same measuring line at Xinqushao,first,we adopted the seismic reflection exploration of primary wave in three levels with the group interval of 10m→5m→1m to catch the master fault of the Yinchuan buried fault,and by tracing upward layer by layer in the order of the three exploration ranges,i.e.1400～400m→600～80m→150～20m,the position of the master fault at ±20m depth under the ground and its offset trace were primarily identified.And then,along the master fault and within the range of 100m at its both sides,9 boreholes of 20.5～100m were arranged for the composite geological profile drilling.The resulting information about the throws of the master fault was obtained,they are 20.34m,9.66m and 2.25m respectively at the depth of 43.75m,20.33m and 13.04m from the ground,and the buried depth of the upper offset point ≤8.34m.At the same time,using the intact core specimen from the fault plane of the borehole No.7,we calculated the dip angle of the fault as 71°at the depth of 55.27m and figured out the exact position of its extension to the earth's surface.Finally,a large-scale trial trench,which is 40 meters long,8～12 meters wide and 6 meters deep,was arranged across the master fault.The trenching revealed that the actual buried depth of the upper offset point of the master fault is 1.5m and there are seismic remains,such as offsets of 5 stages,sand liquefaction and surface rupture,etc.Among the 5 stages offsets,4 events occurred prior to 3170±80 a BP,belonging to the mid to late Holocene paleo-earthquakes.The age of the last event cannot be determined and it is inferred to be the result of the M8.0 Yinchuan-Pingluo earthquake in 1737.In a word,through the comprehensive test exploration,we find that the Yinchuan buried fault is a Holocene active fault,which lays solid base for the next exploration.

GEOMETRIC STRUCTURES AND RECENT ACTICVITY ALONG THE NORTHWEST SEGMENT OF NORTH MARGINAL FAULT OF MAXIANSHAN MOUNTAINS,GANSU PROVINCE

SONG Fang-min, YUAN Dao-yang, CHEN Gui-hua, CHENG Jian-wu, ZHANG Lan-feng, HE Wen-gui, GE Wei-peng, SU He-jun, LU Bin

2006, 28(4):  547-560. 

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The Maxianshan north marginal fault belongs tectonically to the Kunlun-Qilian-Qinling Caledo～nian-Variscan orogenic belt.The northwest segment of the fault locates within the Mesozoic Lanzhou basin,consisting of Xianshuigou-Maquangou,Xinchenggou and Qingshizui sub-segments.The Xianshuigou-Maquangou sub-segment is 7km in length,and comprises two sub-parallel faults,having a general strike of 290°～300°,dipping NE or SW at an angle of 60° or more.The faults dissect mainly the Cretaceous system,and locally act as the boundary of the Cretaceous system with the Ordovician and Jurassic systems.Upwards,the faults cut through the late Pleistocene loess or the gravel bed of gully terrace,appearing as fault scarp or fault escarpment.This sub-segment was the active segment of the whole fault during late Pleistocene to Holocene periods.The faulting of this sub-segment was dominated by left-lateral strike-slipping.The left-lateral displacement along this sub-segment since late Holocene is 5～8m,and the displacement rate is 0.5～1.72mm/yr.The Xinchenggou sub-segment is about 1.6km long,striking 325°and dipping southwest at the angle of greater than 60°.This sub-segment can be assigned to reverse fault,dissecting the Cretaceous system,and is covered with the gravel bed of the third level terrace of the Yellow River and the late Pleistocene loess.This sub-segment,therefore,has no longer been active since late Pleistocene.The Qingshizui sub-segment is about 2.5km long,striking 280°～310°and dipping northeast at angles of 58°～80°,and can be assigned to normal fault.The fault dissects mainly the Cretaceous system,and locally becomes the boundary between the Cretaceous and Ordovician systems.The fault is also covered with the gravel bed of the third level terrace of the Yellow River and the late Pleistocene loess.This may indicate that this sub-segment has ceased its activity since late Pleistocene.Macroscopically,the middle and eastern segments of the Maxianshan north marginal fault,together with the Zhuanglanghe Fault have made up a right-stepped en echelon zone.The faulting process of the former during late Pleistocene-Holocene was dominated by left-lateral strike-slipping,while that of the later by right-lateral strike-slipping,so a compressional step-over was formed between the two faults.Therefore,the Xianshuigou-Maquangou sub-segment can be assigned to shear fault within the compressional step-over,and hence the latest activity of this sub-segment is later than that of the middle and eastern segments of the Maxianshan north marginal fault.

MICROSCOPIC ANALYSIS OF THE TRENCH ACROSS THE SHUNYI-QIANMEN-LIANGXIANG FAULT AT SHUNYI,BEIJING AND ITS IMPLICATIONS

LIN Chuan-yong, CHEN Xiao-de, LUO Hua-chun, SHI Lan-bin

2006, 28(4):  561-578. 

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The faults developed in unconsolidated soft sediments are often macroscopically obscured,so that their occurrence and mode of motion are difficult to be identified only by macroscopic observation.Recently,a lot of data have shown that microscopic analysis is an effective approach to the identification of obscured faults and paleo-earthquake event in soft sediments.Our purpose,therefore,is focused mainly on the exploration of the micro-structural and micro-sedimentological indicators of obscured faults and paleo-seismic events in soft sediments.A case study on a trench dug across the Shunyi-Qianmen-Liangxiang Fault at Shunyi,Beijing is presented in this paper.Microstructural observation reveals that the obscured fault in soft sediments can be traced distinctly under microscopic scale.Microscopically,the fault can be identified by its various appearances,such as distinct slip surface,micro-rupture zone,deformation bands,deformation band shear zone,band of clay infillings,and band of concentration and orientation of clay minerals or clastic particles.Micro-sedimentological analy～sis shows that the disturbance of micro-bedding,as well as the changes of angularity,size and distribution pattern of clastic particles from the beds outside and inside the fault can be taken as the micro-sedimentological indicators of obscured fault in soft sedi～ments.The obtained high D value(～2.5)of the particle size distribution(PSD)is believed to represent sudden seismic faulting event.Our microscopic observations have also revealed that the macroscopic indicators of seismites,such as balls and pillows,loading structures,mass flow,liquid flow and floatation of organics,are also reflected in microscopic scale.We believe that these microscopic indicators of seismite can also be used as the indicators of paleo-seismic event in soft sediments.All the results show that microscopic analysis is an effective method for identifying obscured fault and paleo-seismic event in soft sediments.

DISLOCATION AND DISTRIBUTION CHARACTERISTICS OF THE LINTONG-CHANG'AN FAULT

FENG Xi-jie, DAI Wang-qiang, SHI Ya-qin, LI Jin, REN Jun, HAN Heng-yue

2006, 28(4):  579-588. 

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Lintong-Chang'an Fault is an important boundary fault between Lishan uplift and Zhouzhi-Huxian depression in Weihe basin.By the field survey to the natural gullies,the earth fetching areas,and the excavated slope and chasm for road foundation,we discovered 40 outcrops of the Lintong-Chang'an Fault.According to the measurements of dislocation of the various periods' paleosoil horizons,we get the Quaternary dislocation distribution of the fault,which shows that the fault dislocation in the middle segment is the biggest,so is its activity along this segment.

A PRELIMINARY STUDY ON THE EXPERIMENTAL RESULT OF 2-D RESISTIVITY TOMOGRAPHY SURVEY ALONG TANLU FAULT ZONE IN WEIFANG,SHANDONG

LI Qing-lin, QIN Jian-zeng, XIE Ru-yi, ZHANG Xiao-pu

2006, 28(4):  589-596. 

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The electrical resistivity tomography survey was conducted to detect the active faults along the Tanlu fault zone in Weifang,Shandong province.The results of 2-D resistivity inversion of the Yishui-Tangtou and the Liujazhuang faults indicate that electrical structures on both sides of the fault zone present obvious difference,the resistivity of the hanging wall is low and partially high,while that of the foot wall is high,and the faults are high-obliquity faults.Results show that the resistivity tomography survey is very effective for detection of active faults in urban area.

PARAMETERS SELECTION FOR VELOCITY ANALYSIS IN SHALLOW SEISMIC DATA PROCESSING

WANG Hui, DING Zhi-feng

2006, 28(4):  597-603. 

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Shallow seismic exploration is the main technique in present urban active faults detecting.The detection precision is not only affected by the factors of sources and receivers,but also closely related to the precision of seismic data processing.Velocity analysis is an important step in seismic data processing,which determines the precision of NMO,CDP stack,post-stack migration and time-depth conversion.Considering the properties of low stack folds,shallow objected layers and big background noise of shallow seismic data,the parameters selection for velocity analysis is studied in the paper.Firstly,by analyzing the offsets of different traces in adjacent CDP gathers,and comparing between single and multiple CDP gathers,the principle of how to extract large CDP gathers is proposed.And then,through comparing the velocity spectra derived from different large CDP gathers,velocity scanning interval,time window length,cutting ratio of NMO,etc.,some effective advices on parameters selection for velocity analysis are given,and meanwhile,several noticeable problems in velocity analysis and time-depth conversion are discussed.

DETERMINISTIC SEISMIC GROUND HAZARD MAP IN NORTH CHINA

DING Zhi-feng, F Vaccari, CHEN Yun-tai, G F Panza

2006, 28(4):  604-611. 

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From the strong earthquake activities since 1500,the seismic ground hazard map in North China is assessed using a deterministic approach method.The seismic sources are represented at a set of grid points located at distances of 0.2? from each other.The main inputs for this computation are earthquake catalogue,source mechanisms,the level of seismic activity and the deep structural models.Synthetic seismograms at each grid point are generated by different sources and traveling paths.The method proposed by Panza(1999)was used in the calculation to obtain the distribution map of the maximum ground motion and design ground acceleration(DGA).In the research area,the highest value of DGA is at east of Beijing,with the value as high as 0.75g.It can be found that the cities of Beijing,Shijiazhuang and Taiyuan are located in the area with the strong seismic ground motion.The synthetic results may give the evidences for studying the distribution features of seismic hazard in the North China region and be helpful to the work for the seismic hazard mitigation.

SIMPLIFIED METHOD FOR NUMERICAL SIMULATION OF NEAR-FIELD STRONG GROUND MOTION

ZHANG Dong-li, TAO Xia-xin, ZHOU Zheng-hua

2006, 28(4):  612-622. 

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Besides the site condition,the distribution of sub-sources and expansion of sub-source rupture on finite fault effect the near-field ground motions strongly,too.In order to simulate strong ground motion effectively,we develop a simplified numerical simulation method by numerical Green's function's computation.The whole process can be divided into two steps.At first,in infinite uniform elastic medium,take the finite fault as an exterior source under asymmetry layers,the displacement time histories of overburden layers' bottom caused by all sub-sources can be synthesized by analytic solution.The results can be used as the input for the finite element numerical simulation.Secondly,in asymmetry medium,with local artificial transmitting boundary condition,the explicit decoupled finite element simulation approach is applied to model the near-field strong ground motions.Comparing with former source studies,two ideas are added into the source model.One is that,instead of simple couples source,the earthquake moment tensor is introduced to describe fault attitude and the rupture mechanism,which could express the relationships among force,slip direction and slip-time function of every sub-sources in detail.The dislocation could by equivalent to three-order earthquake moment tensor with 9 force couples and every couple expression includes source parameters,such as fault strike,dip angle and rake angle.The other idea is about the slip-time function.On a finite fault,the inhomogeneous characteristics can be expressed by the nonuniform dislocation distributions and the nonuniform rupture expanding in temporal and spatial space.In this paper,the Brune model is used to characterize the slip-time function.For a certain sub-source,three parameters can define the function,average dislocation,rising time and the rupture time delay.It is feasible of the simplified method of strong ground motion simulation by an example test.According to the source parameters and velocity structures of the 1994 Northridge M_W 6.7 earthquake,long period ground motions of four rock stations are simulated and compared with their records.The simulation acceleration histories and velocity histories are coincident well with the records in durations,amplitudes and envelops.The large acceleration pulse and velocity pulse in the simulation are clear.The simulation results also express engineering characters of hanging wall effect and rupture directivity effect distinctly.All above are well in accord with the ground motion records and earthquake investigation which prove that the approach is reasonable and applicable for seismic hazard evaluation and prediction.

SIMULATION OF THE NEAR-FAULT STRONG GROUND MOTION IN BEIJING REGION

PAN Bo, XU Jian-dong, Haruko Sekigguchi, HE Hong-lin

2006, 28(4):  623-634. 

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On the basis of previous study of the 1679 Sanhe-Pinggu(M8.0)earthquake,which is the biggest event in history ever recorded in Beijing and its adjacent area,we performed a 3-D strong ground motion simulation by utilizing staggered-grid finite difference method to study the distributions of peak ground velocity with different earthquake source models in Beijing region.In the paper,earthquake source models and a transmission medium velocity model are established and the corresponding parameters are given with the accordance to the results from related previous study.Then,using a three-dimensional finite difference computing program of near-fault strong ground motion developed by Graves,the peak ground velocity caused by the destructive earthquake in Beijing area is simulated.In our computation model,the earthquake source is 3km in depth,and a total number of 21,679 observation points on the ground surface is figured out.The transmission medium velocity model is composed of four stratums which are the Quaternary deposit,the upper crust,the upper part of the middle crust and the lower part of the middle crust.With the minimum grid spacing of 0.15km,a total of 2.28?10⁶ grids are generated.Using a time step of 0.02 seconds we calculated the peak ground velocity for 8 seconds duration time.After the analysis of the simulation results,we observed some basic characteristics of near-fault strong ground motion such as near-fault concentration effect of peak ground velocity,rupture directivity effect,hanging wall effect,and basin effect.The results from our simulation and analysis suggest that the source and transmitting medium parameters in our model are suitable and the finite difference method is applicable to estimate the distribution of strong ground motion in the study region.

EXPERIMENTAL STUDY ON RUPTURE PROPAGATION ALONG BURIED STRIKE-SLIP FAULT

DAI Shu-hong, MA Sheng-li, PAN Yi-shan, LUO Hua-chun

2006, 28(4):  635-645. 

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It is important for active fault research and seismic hazard assessment in urban area to study the existence of buried active fault and its possible effect on the earth's surface.Many geophysical and geo～chemical techniques have been developed for exploration of buried active fault,and advanced remote techniques have been used in measurement and analysis of deformation on the earth's surface caused by earthquake on buried fault.However,the relationship between buried seismogenic fault and surface deformation and rupture caused by earthquake needs to be further studied.It is helpful for understanding rupture propagation along buried fault in loose sediment to study the evidence of fault sliding in the overlying sediments with simulation experiments.In this paper,rupture propagation along strike-slip fault in bed rock towards the overlying sediment layer has been studied with simulation experiment and deformation field on the surface of sediment layer has been observed using digital speckle correlation method,in which the effects of fault displacement and thickness of sediment layer were mainly analyzed.The research results indicate that a deformation and rupture zone composed of tension and shear fractures along the projection line of fault in bed rock is gradually formed in the sediments as the fault slips,given a constant thickness of the sediment layer.The larger the fault displacement is,the larger the width of deformation zone and the deformation intensity are.However,the width of deformation zone will keep constant when fault displacement exceeds a critical value,but the deformation will only become more concentrated as fault displacement increases.For a same fault displacement,the thicker the sediment layer is,the wider the deformation and rupture zone controlled by the bed rock fault will be,i.e.the larger the influencing extent of the fault is.However,when the sediment layer exceeds a critical thickness,the deformation pattern of sediment layer is changed.There exists no deformation zone consistent with the strike of fault in bed rock but a large-scale tensile shear rupture zone oblique to the fault strike.The experimental results imply that the critical fault displacement and the critical sediment thickness play important roles in determining the surface deformation and rupture caused by buried fault generated earthquake.

THE BEST COMBINATION METHODS AND APPLIED RESEARCH OF SEISMIC PROSPECTING FOR ACTIVE FAULTS IN URBAN AREA

FANG Sheng-ming, ZHANG Xian-kang, LIU Bao-jin, DUAN Yong-hong, XU Xi-wei, ZHANG Yong-chao

2006, 28(4):  646-654. 

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This paper introduced the basic principles of various seismic prospecting methods and working methods briefly according to the nationwide practices of seismic prospecting for active faults beneath big cities in recent years.Furthermore,it mainly analyzed the available range of different seismic prospecting methods,main achievements and solutions,and discussed the best combination of seismic exploration methods for detecting crustal structure and locating the faults used in the present stage,that is,to trace the faults which are at the depths of hundred meters underground using shallow seismic investigation,to detect the basement faults which are above basement(at depth of kilo～meters)using high resolution refraction sounding,and the deep crustal faults using combined seismic prospecting method of reflection seismic sounding and wide-angle reflection/refraction sounding,and furthermore,to adopt 3-D deep seismic sounding method to get 3-D velocity structure beneath city area.Thus,we can get information about fault attitude and distribution at different depths and a complete image of fault from shallow part to deep part using the combined seismic exploration method.Some application examples are presented in the article.

DESIGN AND IMPLEMENT AN URBAN ACTIVE FAULT INFORMATION MANAGEMENT SYSTEM

YU Gui-hua, XU Xi-wei, SUN Yi, ZHU Jin-fang, ZHANG Lan-feng

2006, 28(4):  655-662. 

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Urban earthquake disaster is mainly caused by abrupt rupturing of active fault.The seismic active fault database on active fault location,slip rates,and earthquake recurrence intervals can help the community effectively reduce earthquake losses,protect against loss of life and damage to property.In United States,New Zealand and other countries,some active fault databases have been built and they provide users with full and open information.In China,the first active tectonics database was built in early 1996.Nowadays,the development of urban active fault exploration makes it possible and necessary to construct an urban active fault information management system(UAFIMS).The UAFIMS aims to construct the basic databases of seismic active faults and their associated hazards as well as the GIS of seismic active fault hazards by utilizing high-performance computer and with the combination of the integrated secondary development of various commercial software.The databases and GIS will be used for urban planning and land use,major project siting,fortification against earthquake,architecture protection,rapid assessment of disaster,government decision-making,and the emergency relief during earthquake by the command departments.We adopt the object-oriented design ideas and method to devise the system,using prototype model for development and object-oriented software technology in VB to invoke ArcGIS background Arc-Objects components library for the integrated secondary development.The system uses C/S model in the LAN and B/S model in the WAN.It has a three-tier structure including user interface,applications and database.The database of exploration results of urban active faults is managed by the ways of classification,tiered storage and thematic organization enquiry,which contains the basic geographic information,geochemical exploration results,electromagnetic sounding data,ground-probing radar sounding data,shallow seismic reflection,deep seismic sounding profiles,as well as drilling data.As a spatial multimedia entity database for data integration,it is a collection of spatial geographical information,image information,text information and data information,and etc.Catering to the needs of results of major fault exploration and seismic hazard assessment projects,the system is designed with the concept of sufficiently displaying the various exploration results and being convenient for users to use and inquire.The application layer can be divided into three types of functions,that is,result displaying and consulting module,professional data analysis and calculation module,and system maintenance module.The system provides users with professional usage habits and simple graphical interface operation,and takes into account,as much as possible,the coordination of system interface to both the local area network and the wide area network.Based on the database of the urban active faults,and supported from spatial analysis,the UAFIMS incorporates geological,geophysical and geochemical data,and comprehensive enquiries and thematic analysis together,and possesses the functions of classification,inquiry,display and analysis,and etc.of the results of active fault exploration and interpretation.The fulfillment of the system provides a solid foundation and technological platform for the quantitative study of active faults,and it also offers scientific basis for urban planning and earthquake disaster reduction.

THE QUENCHING CALIBRATION FOR TRITIUM DETERMINATION FROM FAULT ZONE BY LIQUID SCINTILLATION METHOD

YIN Jin-hui, ZHENG Yong-gang, LIU Yue-xia

2006, 28(4):  663-667. 

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This paper introduces a simple and practical way to construct quenching calibration curve for tritium DPM measurements basing on efficiencies of a series of known activity standard sources and quenching parameter SQP(E)used to define the quench level in Quantulus 1220.Ten standard sources and two test samples were prepared with tritium-free water as quenching materials and progressively added to Hisafe 3 cocktail.A linear curve or polynomial function curve was fitted with each pair of quench parameter SQP(E)and efficiency of standard source.The test sample demonstrated that the error of linear curve was small within routine quenching range of 776 to 785.Therefore,the quenching calibration curve can be beneficial to improving accuracy and reliability of tritium counting.

STUDY ON ESR SIGNAL CENTERS AND MEASUREMENT CONDITIONS FOR DATING OF CALCITE

JIA Li, BAO Ji-fei, YIN Gong-ming, LIU Jing-wei, LI Jian-ping

2006, 28(4):  668-674. 

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Calcite is a common matter in the fault zone and it is often related with fault movement,so its dating is of vital significance for studying the time of fault movement.At present,ESR method is one of the ways for measuring the age of calcite,but there are no final conclusions regarding the ESR signals and measurement conditions of calcite.The samples used in this article were picked from the east of Erhai,Yunnan.According to the preliminary study of the samples,we found that calcite was liable to generate unstable short-lived signal when it was artificially exposed.So before measuring,the samples were kept under the room temperature condition for at least 5 days to eliminate the jamming signals.Generally,in natural calcite,there are many ESR signal centers,among them,the ones,g=2.0040 and g=2.0023,respond well to absorbed dose,and can be used in the dating.Growth curves of these two signals indicate a linear growth at least in the range of 1500Gy.But it is indicated with the artificially fixed known dose method that different microwave powers have to be taken for g=2.0040 and g=2.0023 signals.If we consider the deviation of ED value is smaller than 5%,then the microwave power should be 0.8 or 2mW for the g=2.0040 signal,and the microwave power be 2mW or 5mW for the g=2.0023 signal.

EARTHQUAKE RISK ASSESSMENT OF THE MAIN FAULTS IN HARBIN URBAN AREA

CHEN Li-chun, LIANG Hui, RAN Yong-kang, CHEN Yu-xiang

2006, 28(4):  675-689. 

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In the target area of active fault surveying around Harbin City,the latest rupturing ages of the main faults are all early or middle Pleistocene,and there are no evidences to indicate that rupture has occurred on these faults since late Pleistocene.By synthetical analysis of technical route of earthquake risk assessment of urban active fault,seismic environment and division of potential seismic source zone in research area around Harbin City,and activity characteristics of the main faults in target area,the maximum magnitude of probable future earthquake on these main faults are forecasted in this paper.And then probabilities of middle-strong earthquake occurring in the next 100 years are calculated for both the whole target area and its three single faults according to the two scales of Xin'an-Dongmeng active block and research area on the basis of adjusting properly the probability technique of earthquake risk analysis for engineering seismology.In conclusion,the probable future maximum magnitude on the main faults in target area are all M_S 5.5,but there is bally low probability of damaging earthquake(M_S>4)occurring on them.No doubt,there are still a few uncertainty and unreliability to these results because of the hypothesis for calculation and deficient samples for statistic.However,in terms of current level,the technique of earthquake risk assessment in this paper is more suitable to use for such still areas as Harbin,where the tectonic activity is quite weak since late Quaternary.And furthermore,it can provide at a certain extent tutor or reference for surveying and prospecting of active fault in other cities.