欧亚大陆及西太平洋边缘海瑞利面波层析成像研究

利用亚洲、欧洲及西太平洋边缘海地区台网114个数字地震台,搜集了40°W~180°E,40°S~80°N范围内近万个地震事件,并从中挑选出1982~2006年间震级在5.0~7.0之间、震源深度小于100km的1800余个事件。经过筛选,共得到周期在8~200s之间10450余条质量较高的瑞利面波频散曲线,这些面波所通过的大圆路径很好地覆盖了欧亚大陆及西太平洋。本文首先对原始记录进行预处理,测定面波频散曲线,包括截取Rayleigh面波,进行频率时域分析等,以得到实际频散数据。然后对研究区域进行网格划分,反演网格点附近的纯路径频散曲线。即采用网格化纯路径频散反演方法得到各块的纯频散数据。最后由得到的每块纯频散数据作为观测数据,并利用LSQR、SVD等广义线性反演方法,对每一块的纯频散曲线进行反演求取该单元的S波速度随深度的分布。

Tomographic image of Rayleigh Surface Wave in Eurasia and western Pacific marginal seas

More than 1 800 seismic events(which occurred from 1982 to 2006,distributed in the range of 40°W~180°E,40°S -80°N,with magnitudes in 5.0~7.0 and focal depths shallower than 100 km)are selected from nearly 10,000 events recorded by 114 digital seismic stations in Asia,Europe and west Pacific networks.Totally 10450 accurate Rayleigh surface dispersion curves are employed for dispersion inversion,and the distribution map of Reyleigh wave group velocity in 28 periods from 8 S to 200 S for Eurasia continent and marginal seas of west Pacific are obtained.The great circle routes of surface waves cover Eurasia and the west Pacific Ocean.This paper preprocesses the original datum to determine surface dispersion curves at first, including the steps as following:intercepting Rayleigh surface wave,analyzing in time domain,to obtain the actual datum of dispersion.Then it lattice partitions the researched zone,and calculates the group velocity in theory,which means getting the datum of pure-path dispersion by inversion method of dispersion curve of latticing pure-path.At last,it inversed the pure-path dispersion to get the velocity distribution of S wave along with the depth of every unit by making use of datum for each unit as observed datum and by generalized inversion method like LSQR,SVD and so on.