摘要
纵横波联合探测可以获得丰富的地下结构信息。纵横波速比和岩石泊松比在预测岩石圈的岩性、物性等介质属性方面有重要的作用。通过对比南海中北部OBS2006-3地震剖面垂直分量和径向分量上的纵横波走时、视速度以及质点运动轨迹,识别出了转换横波震相。本文以OBS8和OBS10台站的数据为例,说明了横波识别的方法,并在拟合好的P波速度模型基础上,利用RayInvr软件对转换横波震相进行了射线追踪,确认了PwSs3、PgSs3、PmS等几组转换震相,计算了这两个站位下的波速比和泊松比。根据OBS2006-3测线下地壳高速层的P波速度(VP=7.20—7.25km·s-1)、S波速度(VS=4.20—4.23km·s-1)、泊松比(0.24)等参数,初步推断下地壳高速层是由上地幔岩浆底侵作用形成。
Applying the joint exploration of P-wave and S-wave,the complex subsurface crustal structure can be obtained.The association of P-wave velocity and S-wave velocity is very sensitive to the physical state of rocks,and is thus very useful in lithological studies.Compared with travel-time of P-wave and S-wave,apparent velocity and particle's moving trajectory in vertical-component and radical-component seismic sections,converted S-wave phases were identified in OBS8 and OBS10 along the profile OBS2006-3 in the mid-northern South China Sea.In this paper,taking these two OBSs as examples,we discussed identification and analysis of converted S-waves in detail.A few of S-wave seismic phases(e.g.,PwSs3,PgSs3,PmS) were identified based on the optimum P-wave model using the software Rayinvr and the ratio of Vp/Vs and Poisson's ratio are calculated beneath these two OBSs stations.Based on P-wave velocity(VP=7.20-7.25km·s-1),S-wave velocity(VS= 4.20-4.23km·s-1) and Poisson's ratio(0.24),we suggest that the high velocity layer in the lower crust has a mafic composition that may originate from magmatic underplating.