In accordance with the requirements of "Eleventh Five-Year" national scientific and technological support projects,an intensive seismic observation network consisting of 26 seismic stations was established at the Three Gorges Reservoir area in the section of Hubei Province in March 2009(21 short-period seismographs,5 broadband digital seismographs).From March to December,2009,2995 M_L-0.8～2.9 earthquakes were observed during the trial impounding of the Three Gorges Reservoir(water level rose from 145m to 172.8m).Using the double difference earthquake location algorithm,2837 earthquakes were relocated precisely.The results show: The pattern of small local earthquake swarms in Three Gorges Reservoir area took on a linear distribution or mass-like cluster distribution,the mass-like clusters of events were generally within the distance of 5km from waterfront,and the linear distribution of the earthquakes could be extended to a distance of 16 kilometers away from waterfront.In Hubei section of Three Gorges Reservoir,earthquakes were mainly concentrated in the northern end of Xiannüfeng and Jiuwanxi Fault in the vicinity of the Xiangxihe river,and along the banks of the Yangtze river at the east of Xietan village and at Shenlongxi area on the northern bank in Badong region;the focal depths were less than 10km,and 4km in average.Earthquake frequency of the reservoir region had a positive correlation with reservoir water level fluctuation,indicating that the seismicity belonged to the reservoir induced earthquakes.Along the Shenlong river in the reservoir area,earthquakes showed three linear distributions in the northern Badong County,which was related to karst distribution.There are underground rivers along carbonate strata.When reservoir was impounded,water permeated into the underground rivers,thus inducing earthquakes.Earthquakes in the areas on the cross-river segment of Xiannüfeng Fault,the Jiuwanxi Fault and at the areas west of Xietan,Shazhen and Xizhen,may be related to the softening of discontinuities,such as the Nukou Fault,the Xiannüfeng Fault or the bedding joints,etc.,which would lead to failure of rock masses,thus,inducing earthquakes.However,convincing conclusions about the triggering mechanism still need further study.In addition,in the areas south of Wenhua and Yanglin of Zigui County and at Rangkou town east of Badong county,there are mining-induced earthquakes at the mines nearby.And on the shores of the reservoir,there are some collapse earthquakes.

In the paper,according to the related factors and characteristics of identified reservoir induced earthquakes,the parameters of reservoir induced earthquake database and library structure have been determined.Based on the database functions of ARCGIG geographic information system software,the reservoir induced earthquake database contains 131 reservoir induced earthquake cases in the would, 110 Class-Ⅰlarge reservoirs(larger than one thousand million cubic meters),200 ClassⅡlarge reservoirs (larger than one hundred million cubic meters and less than one thousand million cubic meters) and 70 reservoirs with dams higher than 100 meters in China.It has the functions of quick query,statistics and icons.After the Wenchuan earthquake,aftershocks endangered many reservoir's dams and people who were taking part in earthquake rescue and relief operations.Two days after the M_s8.0 Wenchuan earthquake,the distribution and basic information of large reservoirs in Sichuan Province and nearby regions was submitted.The government made timely earthquake emergency response decisions to ensure a safe relief.The reservoir induced earthquake database is not only a method provided to the government for quick decision-making,but also can be used nation-wide.

The geodatabase of scientific investigation of Wenchuan earthquake stores many field investigation data,such as the data of field geological survey sites,the surface rupture belts,the Quaternary faults in the earthquake region,paleoseismological trenches,folds,etc.Moreover,it includes some collection data,such as strata data,the catalog of the Wenchuan mainshock and aftershocks,the relocation catalog of aftershocks of the Wenchuan earthquake,the catalog of historical strong earthquake.The field data are recorded,edited,analysed,mapped and output with ArcGis,a powerful function in Gis software.The geodatabase of scientific investigation of M_S8.0 Wenchuan earthquake was initially established,which includes the basic seismological information and realizes the integrated management of spatial location and attribute information.Data can be queried,analyzed and processed for the need of the correlation analysis of the data.Seismic tectonic map and surface rupture map can be drawn with the geodatabase,which can provide the basis for the determination of safety distance from the risky seismic rupture zones in post-disaster reconstruction and for the construction of the Wenchuan earthquake geographic information system.

1:250,000 regional seismotectonic map is one of graphic documents achieved in the urban active fault survey project.At present,the 1:250,000 regional seismotectonic maps of various cities are drawn mostly basing on the existing 1:200,000 geological maps.The available paper-made 1:200,000 geological maps are the graphic documents under Beijing 54 Coordinates Systems.However,according to Stipulation on Technical System for China Earthquake Active Fault Surveying issued by China Earthquake Administration,the 1:250,000 regional seismotectonic maps are the graphic documents under Xi'an 80 Coordinate Systems.This article introduces the basic concepts of coordinates systems and the map projection and proposes explicitly that when scanning and digitizing paper geological map,the coordinate's projection parameters indicated in the paper geological map shall be taken for setting up projection information.The conversion of screen coordinates to map coordinates is realized through space coordinate registration,and by projection conversion,the Beijing 54 Coordinates System is converted to Xi'an 80 Coordinates System.Finally,with the aid of ArcGIS software,the 1:250,000 regional seismotectonic maps are compiled based on 1:200,000 geologic maps.

Shallow seismic surveying is a common method applied to the research of blind fault activity at the Quaternary stratum region,especially in urban area.The bifurcating,uniting,bending,intermitting and ending off of reflection waves on stacked time section are important signs which are often used to judge the existence of blind fault.At the northern area of Songhuajiang River in Harbin City,we finished two seismic reflection profiles.On the shallow seismic reflection profiles of Lugangtun and Jubaotun,the T₀ wave group corresponding to the interface between Cretaceous sand-mud stone and lower Pleistocene gravel is clear.T_0-1 reflecting wave group corresponding to the contact surface between gravel and clay,or fine sand and gravel,is also clear.Based on the stacking seismic profiles and borehole data,we conclude that the Ashihe fault offset the bottom stratum of lower Pleistocene,and Binzhou fault cut off the bottom stratum of upper Pleistocene.By building high quality composite drilling geological profiles,dating the samples from bores,and contrasting stratum from one bore to the other,we consider that the Ashihe fault does not offset the Quaternary formation,the fault may only exist in Cretaceous sand-mud stone.The Binzhou fault is only an early Pleistocene fault;it doesn't offset the late Pleistocene formation.Finally,we think that the bifurcating,bending,intermitting and ending off of seismic reflection wave group on Luegangtun and Jubaotun seismic profiles are not the result of fault activity,but the phase change of Quaternary formation.

The Altyn Tagh,Kunlun and Haiyuan Faults are three major left-lateral strike-slip faults with high geologic and GPS-derived horizontal slip rates as well as frequent surface-rupturing earthquakes in the northern Tibetan Plateau.There exist local structures,such as pull-apart basins in stepovers and sag ponds,where fine-grained and/or organic interfaulting sediments have been continuously filled and co-seismic faulting traces have been well preserved in those sediments.Trenching across the strike-slip faults and those local structures,stratum-logging of the trench walls and structural-stratigraphic examination can uncover basic features of the permanent and cumulative geologic deformation zone of a strike-slip fault that has experienced several surface-rupturing earthquake cycles.The geologic section of the Banguoba trench 9km east of Old A'kesai Town across the recent traces of the Altyn Tagh Fault records 7 paleoearthquake events with a co-seismic left-lateral slip of 7±1m for the latest event and its cumulative geologic deformation zone is only 8m in width.The geologic section of the western Old A'kesai trench across a pull-apart basin of the Altyn Tagh Fault records at least 4 paleoearthquake events and its permanent and cumulative geologic deformation zone is only 13m in width.The geologic section of the Xidatan trench across the Kunlun Fault reveals 5 paleoearthquake events and their cumulative geologic deformation zones are 12～13m in width.The Maqin trench across a pull-apart of the Kunlun Fault also reveals 5 paleo-earthquake events and most of the structural deformation,about 15m wide,is concentrated in the pull-apart,while the widest structural deformation,including the associated distortion nearby the boundary fault of the pull-apart,is less than 35m.Two trenches excavated across the southern and northern boundary faults of the Songshan pull-apart basin along the Maomaoshan-Laohuashan segment of the Haiyuan Fault show up 6 paleoevents and their permanent geologic deformation zones are less than 10m wide for single boundary fault.Of course,as a extensional jog,the pull-apart basin over a hundred meters wide will experience severe tensional and transtensional surface ruptures during an earthquake,and the pull-apart basin itself may be taken as one part of the permanent geologic deformation zone.Thus,the repeatedly faulting of the Altyn Tagh,Kunlun,and Haiyuan Faults during the past several surface-rupturing earthquake cycles is localized along their strike and the width of their permanent geologic deformation zone for a single strike-slip fault is over 10 meters,but less than 30 meters in general.

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 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.

Owing to strong and permanent Cenozoic re-orogenic processing, a lot of EW-striking active thrusts and folds have been developed in Tian Shan, resulting in crustal shortening in NS direction. There also exist NW-striking transform-like strike-slip faults that cut the Tian Shan and accommodate uneven crustal shortening larger in the west and smaller in the east. The seismogenic structures in and around the Tian Shan mainly include EW-striking thrust ramps or blind thrusts and NW-striking transform-like strike-slip faults. The 2003 AD Bachu-Jiashi earthquake is located at south of the Kalpintag nappe. A NE-trending deep seismic reflection profile about 50km long across the epicenter has been conducted after the earthquake. From this reflection profile four blind faults are identified. Together with earthquake relocation, these identified blind faults are used in the paper to interpret the seismogenic structures of the 1997 AD Jiashi strong earthquake swarm and 2003 AD Bachu-Jiashi earthquake. The 1997 AD Jiashi strong earthquakes were generated mainly by a NW-striking buried transform-like strike-slip fault, while the 2003 AD Bachu-jiashi earthquake by blind thrusts in front of the Kalpintag nappe.

The Xiaodianzi-Maobu segment is part of the Anqiu-Juzian Fault in the Tancheng-Lujiang Fault zone. It starts from northeast of Xiaodianzi village, Juxian County in the north and terminates at Maobu, Juxian County in the south. The fault segment has a general strike of 10°～20°, dipping northwest or southeast at an angle of 60°, and has a length of about 30km. The segment can further be divided into 5 sub-segments: the Xiaodianzi-Qijiazhuang, Yuanhe, Kushan-Xilianci, Qingfengling and Sanzhuang-Zhaike sub-segments from north to south successively. These 5 sub-segments are aligned in right or left-step en-echelon, appearing as a brush structure converging to the north and diverging to the south. The fault segment appears as distinct lineation on satellite image or aerial photo, and geomorphically, as distinct bedrock scarp. According to field observation on natural exposures or trench logs, as well as dating results of samples collected from the fault segment, it can be deduced that the latest faulting event occurred in early Holocene and was dominated by right-lateral strike-slip with compressional reverse faulting component. The distinct horizontal fault striate is well developed along the fault plane and the drainage system crossing the fault segment is right-laterally distorted. This corroborates the right-lateral strike-slip of the fault segment. Field measurement of displacement and dating of the relevant samples have indicated that the displacement amount of the fault is 64～73m, and the displacement rate is 0.91～1.04mm/a in the past 70ka, while in the past 11ka, the displacement is 5.5～7.8m and displacement rate is 0.46～0.65mm/a. The reverse faulting along the fault segment can also be recognized in exposures or trench logs. It can be observed that the Cretaceous or Paleocene system is thrusted over the Quaternary system, making a distinct fault scarp landform. Field measurement of fault scarp and laboratory dating of relevant samples have revealed that in the past 11ka the vertical displacement along the fault segment is 2.3～3.8m and the displacement rate is 0.17～0.32mm/a. In the same period, the right-lateral displacement is 2～3 times as large as the vertical displacement.

This paper introduces the results of shallow seismic exploration on five traverse lines across the Huangzhuang Gaoliying buried fault in the vicinity of Lishuiqiao,Beijing area. The section of the Huangzhuang Gaoliying fault in the vicinity of Lishuiqiao can be distinguished distinctly on the spot map,but the other sections of the fault along river valley are undistinguishable. The shallow seismic exploration and geological information reveal that the velocity model of the shallow part around the Lishuiqiao area is characterized by 4-layer structure. The layers 1 and 2 are located at a depth range of 0～150m beneath the surface,and they can be assigned to Tertiary or Quaternary deposits,having a velocity of 800m/s to 2000m/s. The layers 3 and 4 are identified at a depth range of 130m to 300m,which are bedrock consisting of mudstone and sandstone,having a velocity of larger than 2000m/s or 2500m/s. At shallow depth,the Huangzhuang-Gaoliying Fault in Lishuiqiao area is composed of two sub-parallel faults about 1300m apart from each other. The two faults are N23°E-striking,dipping southeast at an angle of 22° for the western fault and 87° for the eastern one. At a depth of 634m the two faults converge into one fault,appearing as a branching fault. The buried depth of the highest point of the hanging wall of the fault is 101m,while that of the footwall is 109 m. The throw of the fault is about 8m. It is concluded,therefore,that the fault is a normal fault with strike-slip component,dissecting the T₂ and T₃ stratigraphic interfaces.

The Youjiang Fault zone is located in the Guixi (Western Guangxi) fault block region. Since the beginning of seismic records,22 earthquakes of magnitude 4.0～6 occurred in this region,among which the largest one is the magnitude 6/2 earthquake occurred in the area between Leye,Guangxi Autonomous Region and Luodian,Guizhou Province in 1875. Of these events,15 earthquakes of magnitude 4.0～5.0 occurred on the Youjiang Fault zone. The Tianlin Bagui M5.0 earthquake of 1962 and the Pingguo M5.0 earthquake of 1977 had caused certain damages of basic installations in the regions. Obviously,the Guixi region is an active region of moderate earthquake,and the Youjiang Fault zone is an active belt of moderate earthquake,which plays an important role in the seismicity in Guixi fault block region and in the territory of the Guangxi Autonomous Region. Based on the interpretation and analysis of satellite images,aerophotos,and large-scale topographic maps,as well as field investigation,a line of geologic geomorphic evidence of late Pleistocene activity of the Youjiang Fault zone have been obtained,and the left-lateral displacements on the fault zone have been measured. This paper presents all these results and provides the horizontal and vertical slip rates of the fault zone since mid-late Pleistocene. The Youjiang Fault zone can be divided into 3 segments. They are the west of Bose,Bose-Silin and Silin-Tanluo segments,each of which can be subdivided into several sub-segments. The offset of late Pleistocene terrace deposit and talus can be observed along each segment of the fault zone. The ages of the deposits have been dated to be (3.28±0.25)×10⁴a BP～(10.16±0.79)×10⁴a BP. Geomorphically,the fault zone controlled the development of the Bose-Tiandong late Quaternary basin. A series of fault valleys,troughs,and scarps were developed along the fault strand,while the drainage system crossing the fault zone was left-laterally offset. According to the comparison of the amplitudes of vertical and horizontal displacements on the fault zone,it is inferred that the activity since late Pleistocene of the fault zone has been dominated by left-lateral strike-slipping accompanied by extensional differential motion. The horizontal displacement rate since late Pleistocene on the fault zone has been determined to be 1.47～1.98 mm/a,the vertical displacement rate since middle Pleistocene is 0.74～0.76 mm/a,and the vertical displacement rate since late Pleistoce is 0.1～0.35mm/a. All these values are significantly lower than those on the fault zones surrounding or within the Chuandian fault block. The recent results of GPS observation support also this conclusion.

In this paper,the relation of time,space and intensity characteristics,as well as focal mechanisms of earthquakes to fault activity in Beijing area has been analyzed.A tectonic deformation model for the upper crust of this region is developed in this paper in the light of the quantitative analysis of fault activity.The results show that the earthquakes in this region are distributed mainly along the NWW direction,forming a concentration belt of earthquakes.In addition,several earthquakes of above magnitude M_S 4.5 occurred along the NE-or NEE-trending faults.These two sets of fault form a conjugate fault system,on which earthquakes occur alternately in different active periods,and the average release rate of creep energy corresponds to the occurrence of one M_S 4.2 earthquake per year.The crust of Beijing region can be divided in to the Yanshan,North Shanxi,Taihangshan and Central Hebei blocks,which have an irregular boundary along the NWW direction.Under the action of the NEE-directed principal compressive stress,these NWW-arranged blocks were easily activated,resulting in concentration belts of earthquake of a certain scale along block boundaries.Moreover,earthquakes of above magnitude M_S 4.5 occurred along the conjugated NE-or NEE-trending faults.

The inner part of the Sichuan-Yunnan rhombic block is dissected by the Lijiang-Xiaojinhe Fault, and hence can be subdivided into Northwest Sichuan sub-block in the north and Central Yunnan sub-block in the south. The eastern boundary faults of these two sub-blocks are regularly characterized by left-lateral strike-slip, while the western boundary faults are characterized by right-lateral strike-slip. The slip rate of both the eastern and western boundary faults are significantly different. All these phenomena may indicate the composite movement of these sub-blocks characterized by southeastward horizontal slipping associated with clockwise rotation around a vertical axis during the Cenozoic time. Among them, the horizontal slip rate of the Southwest Sichuan sub-block is 5mm/a, and the angular velocity of clockwise rotation is about 1 4°/Ma, while those of the Central Yunnan sub-block are 3.5mm/a and 1 5°/Ma, respectively. About 90 oriented samples have been collected from Paleogene strata in Yaoan, Dayao, Yongren and Beimajie of Kunming within the Central Yunnan sub-block. The vectors of remanent magnetism of each sample (measured magnetic declination and inclination) have been obtained through alternating field demagnetization and thermal demagnetization. The comparison between the measured magnetic declination and the expected value shows that the accumulated clockwise rotation of the Central Yunnan sub-block of the Sichuan-Yunnan rhombic block since early Miocene has reached up to 30°～48°. The feature represented by the entire rotation of the sub-blocks accompanied by left-lateral slipping along the boundary active faults is consistent with the kinetic model of clockwise rotation of the block in left-lateral strike-slip faulting region.

This paper demonstrates the results of shallow seismic exploration of the Liuwu-Dafosi Fault in the vicinity of Lhasa City. On spot map, the segment of the fault in mountainous area can be identified distinctly, but the segment in river valley is unidentified. Shallow seismic exploration reveals that the fault dissects Tertiary or Quaternary strata. Geological interpretation of shallow seismic reflection profile reveals a velocity structure of five layers. Layer 1 to layer 4 have a velocity ranging from 0.8km/s to 2.0km/s or 2.8km/s, and can be assigned to Tertiary or Quaternary strata. Layer 5 has a velocity ranging from 3.0km/s to 4.0km/s, which is supposed to be granite bedrock according to its scattered distribution in CDP stacked section and geological evidence. The Liuwu-Dafosi Fault can be identified at 320m distance of the shallow seismic reflection profile located to the southwest of the Lhasa City. The fault is dipping northeast at an angle of 80?, the highest point of which is at 100m depth. It is determined that the fault is an active reverse fault.