The Study Of 3D Velocity Structure And Anisotropy Under Shanghai And Its Neighboring Area

The East China, specially the lower Yangzi-South Yellow Sea area is the importantstrong and active earthquake area in our country.Shanghai and its neighbour area arelocated in the Yangtze River delta.It belongs to the Yangzi land parcel and is one ofone of our country economic development strategy important places.This is an area ofmany economic developed cities with high density of populatiion.But an extremelycomplex structure of earth's crust is under it and natural earthquakes are relative quiteactive,even sometimes strong earthquakes occured.It has the following characteristicsin this area:the great number of tall buildings and so on.As the area is in theory, it hasthe significance and the practical application value to analyze its earth'sstructure,verify the background of its deep structure in earthquake monitor, earthquakeprediction and project earthquake.This present paper has mainly done followingseveral aspects in the research work:First we inverse crust P wave and S wave velocity structure under shanghai and it'sneighbor area using seismic tomogrphic image method,and we get this area velocityperturbation,then we give the critical explanation.On the basic of better understanding about how to use teleseimsic waveform and ofknowing about receive function development history, extraction,inversion and stackprinciple methods,we have debugged the receive function extraction and inversion re-lated procedure.Referred to the Commom Conversion Point Stack method which wasbrought forward by Dueker et al. 1997,we debugged the stacking programme about h-ow to get the discontinuity.Here we has collected some teleseismic events which were observed byjiangsu,shanghai and zhejiang seismic network since 2002,then we selected,filtered,at last wegot receiver functions.We selected these receiver functions,removed those bad qua-lity receiver functions,stacked these good quality receiver functions,then we get radialcomponent and tangential component receiver functions about 42 seimic stations.Aft- er inversing radial receive functions,we got 1D crust S wave velocity structure underthese stations.Combining local deep Seismic Sound information,we analyzed velocitystructure under every station,then we think that s wave velocity change suddenly atthe depth of Moho surface and get up 4.3km/s.The result shows that the cruststructure under jiangsu province is complex,inscipally there exist low velocitylayer.The earth-quakes maybe be related to complexity about deep crust structure background,or berelated to the complex degree about deep crust structure, especially be closely relatedto low velocity layer and high conduct layer.The poisson's ratio is a little high in Suqian,Liyang,Wenzhou.In these areas,thepoisson's ratio is higher,the seismic activity frequently is high and there has the com-plex earth's crust speed structure. This characteristic is obviously different from theneighbor area.It basically presents that the poisson's ratio is lower in the weak earth-quake area or stable block body,but the poisson's ratio is higher in earthquake pronezone.We process these 243 receive functions by filtering and calculate the conversionpoint at 33km,410km and 660km stack depth for every receiver function.After dyna-mic correction for common conversion point at stacking line,we use 100km as radiusfor stacking and get the result that the average depth of 410 and660 discontinuity isabout 410±20km and 670±10km respectively.The 410 and 660 discontinuity underProfile 1 are clear comparatively, along the longitude from west to east, the positiongradually deepens.At last we have done the anisotropy distributed situation under shanghai seismol-ogical array stations with the depth which is based on PpSms, p660S and the SKSphase.Meanwhile we analyze the distribute about anisotropy reader this area crust usi-ng using the receive function PS converted wave, thus obtain the anisotropic parame-ter and approximately the distributed range.