Applcation Of CSAMT For Active Fault Exploration In New District Of Changping,Beijing

Study of the earthquake shows that the mechanism of the earthquake occurrence isrelated with the deep crustal tectonic activity. The exact location of the active faults isalways the most severely damaged area when the earthquake happened, shallowburied active faults are more easily to form the quake hit zone,which pose a directthreat to the city and engineering and cause huge losses to the people and economy. Atpresent, the technology of modern engineering also cannot resist the earthquakedamage,therefore, so as to keep the earthquake damage to a minimum, only at theearly stages of the urban construction, detect the fracture position, occurrence andactivity clearly, can we avoid the location of the active faults reasonablely in theplanning stage.The detection and evaluation of the city buried active faults have greatsignificance for earthquake disaster reduction.In many methods of detecting the city buried active faults,the CSAMT method hasbeen widely used and achieved remarkable results.The full name of CSAMT isControlled source audio-frequency magnetotellurics, is a frequency domainelectromagnetic sounding method, with the characteristics of great depth, highresolution, strong ability of disturbance rejection etc.During author’s graduate studying period,I luckly participated in the project ‘BeijingChangping Planning New Regional Prophase Engineering Geological ExplorationWork’（Item No.：BJJG-2009-181-01） from Beijing Geology And MineralResources Exploration Bureau.In the project,author is responsible for the subprojectactive fault assessment by CSAMT.Therefore,it has theoretical and practicalsignificance to choose the subproject as the research object of the thesis.Changping new city zone is located in the central Changping District,the maindevelopment of the structures in the district is NW and NE, Nankou-Sunhe fault in theNW direction, and four faults in the NE direction.The main work of the subproject isto dissect the exect location,the structure condition in the stratum and the deepdevelopment of the NW Nankou-Sunhe fault and NE Shisanling decken structure bycontrollable source sounding CSAMT method,and make a comment on the activity of the two faults in geological condition.Controlled source sounding CSAMT method in the detection of Beijing Changpingnew district had clearly reflected the fault location,tendency and distance and theburied depth of bedrock surface on both sides of the fault.The trend of theNankou-Sunhe fault is about310°，and the tendency is SW,and the inclination is70°-80°,SW plate drops,NE plate rise,as a normal fault,the faulted formation belowground about4.0m.Compared with the existing data,the Nankou-Sunhe faultBaifu-Baishan period offsets to the NE500-800m from the cognitiveposition.Nankou-Sunhe faulted formation in the Holocene period,is a Holocene activefault, comprehensive evaluation shows that it has big risk to the engineering.The trendof Shisanling decken fault is NE-NNE,the tendency of fault surface is ES,thedistribute length of plain area is15km.In the middle period,it has been cut off byNankou-Sunhe fault.The location of the fault is in accordance with the anteriordetective results,with no obvious signs of activity since the Quaternary,which belongsto the pre Quaternary general fault,Quaternary overburden thickness more than60m,the potential hazard has been comprehensive evaluated as”no”.Taking the fact about Nankou-Sunhe fault Baifu-Baishan period offsets to NE fromthe cognitive position into consideration,the conclusion gives a further worksuggestions,provides reliable basic data for the new town planning stage of regionalgeological survey in Changping Beijing.