华北地区地下介质波速比值(V_P/V_S)研究  

STUDY ON WAVE VELOCITY RATIO(V_P/V_S) OF UNDERGROUND MEDIA IN NORTH CHINA

作　　者：张学民[1] 刁桂苓[2] 束沛镒[3] 刘素英[2] 

机构地区：[1]中国地质大学地球物理与信息技术学院,北京100083 [2]河北省地震局,石家庄050021 [3]中国科学院地质与地球物理研究所,北京100029

出　　处：《地震地质》2004年第2期305-317,共13页Seismology and Geology

基　　金：国家重点基础研究发展规划项目 (G19980 4 0 70 4 )资助

摘　　要：文中利用分别独立反演得到的华北地区 16个台的S波和P波速度结构 ,计算了各台站下方分层速度结构各层的波速比值 ,发现在强震区的波速比总体上高于弱震区 ,且地壳中的一些低速层位会出现 >1 8的波速比值 ,而在弱震区或稳定块体内部 ,各层波速比一般都低于正常波速比 1 732 ,平均值甚至 <1 7;在过渡区域 ,如位于盆地边缘或稳定块体边缘的台站 ,其波速比值有高有低 ,一般情况下 >1 732。在此基础上 。In this paper,based on available S wave and P wave velocity structures beneath16seismic stations in North China,wave velocity ratios for every velocity layer beneath these stations are calculated.According to their seismicity and geographic locations,these stations are divided into three types and discussed sepa-rately.In macroseismic area,the V P /V S ratio is systematically higher than that in microseismic area,and the V P /V S ratio of some low-velocity layers in mid-lower crust is greater than1.8.In seismically quiet area or at interior of stable block,however,the V P /V S ratio is relatively stable for the whole crust and upper man-tle,in many layers of which the ratio is less than the normal V P /V S ratio(1.732).In transitional area,such as the marginal area of basins or stable blocks,the number of layers with high V P /V S value becomes less,but the average V P /V S values beneath the stations are generally still greater than1.732.Moreover,beneath the stations in microseismic area,a layer of more than10km thickness is recognized,which has never been found in macroseismic area and may reflect the old continental nucleus or crystalline basement.Stations in the same tectonic unit of transitional area have the same S wave velocity structure,which might be the result of regional tectonic activities. In addition,the contour maps of V P /V S and S wave velocity at10km,15km,20km and25km depths were plotted and analyzed.The results showthat at10km depth,taken the TaihangMountains as a bound-ary,the V P /V S values in the western area are higher than those in the eastern area;but at greater depth,the V P /V S is higher in the eastern area,and especially much higher in Xingtai earthquake area at25km depth.It can be seen from S wave velocity images,that the velocity differences between the eastern and western areas separated by the TaihangMountains are very significant all the time,and there is no evidence of mixing-up even at25km depth.This may indicate that the Taihang Mountains is an evident m

关 键 词：波速比 低速层 地震学 地质构造 地下介质 

分 类 号：P315.31[天文地球—地震学]