多层介质中利用sPn与Pn到时差确定震源深度的研究  

Determination of focal depth using the travel time difference of sPn and Pn waves in multilayer medium

作　　者：王瑶 万永革[1,2] WANG Yao;WAN Yongge(Institute of Disaster Prevention, Sanhe 065201, Hebei, China;Hebei Key Laboratory of Earthquake Dynamics, Sanhe 065201, Hebei, China)

机构地区：[1]防灾科技学院,河北三河065201 [2]河北省地震动力学重点实验室,河北三河065201

出　　处：《地震工程学报》2021年第6期1294-1302,共9页China Earthquake Engineering Journal

基　　金：河北省地震科技星火计划(DZ20190415002);国家自然科学基金(41674055,41704053)。

摘　　要：为利用sPn与Pn波的走时差测定震源深度,进一步提高地震震源深度的测定精度,推导多层介质下sPn与Pn波的走时差与震源深度的关系,发现走时差与震中距无关,只与震源深度及区域地壳速度模型有关。震源在同一层中,走时差曲线的斜率不变,而当震源位于不同层中时,sPn-Pn走时差曲线的斜率不同,并呈分段直线的走时差曲线形态。地壳速度结构纵向越不均匀,多层和单层介质下利用sPn-Pn走时差计算的震源深度误差就越大,走时曲线的各分段直线斜率相差越大;探讨地壳中sPn与Pn波传播路径相同但波速不同的单层地壳速度模型,发现单层介质下波速越大,测定的震源深度越大;对于同一地区相同的地壳分层结构,测得的震源深度随着泊松比的增大而减小。基于前人给出的中国五个典型块体多层平均地壳模型,给出sPn-Pn走时差与震源深度计算公式速查表。To measure the focal depth by using the travel time difference between sPn and Pn waves and further improve the measurement accuracy,the relationship between the travel time difference of sPn and Pn waves in multilayer medium and the focal depth was deduced,and it was found that the travel time difference is not related to the epicenter distance,but only related to the focal depth and the regional crustal velocity model.The slope of the travel time difference curve remains unchanged with the source in the same layer,while the slope of the curve is different with the source in different layers,showing as a piecewise straight line.The more uneven the crustal velocity structure is in the longitudinal direction,the greater the focal depth error calculated by sPn-Pn travel time difference is,and the greater the slope difference of each segment of the travel time curve is.The single-layer crustal velocity model of sPn and Pn waves with the same propagation path but different wave velocities in the crust was discussed,and it was found that the measured focal depth increases with the increase of wave velocity in single-layer medium.For the same layered structure of crust in the same area,the measured focal depth decreases with the increase of Poisson's ratio.Based on the multi-layer average crustal model of five typical blocks in China provided by previous studies,a quick look-up table for the formula to calculate the focal depth by using the sPn-Pn travel time difference was presented.

关 键 词：SPN震相 Pn震相 走时差 震源深度 多层地壳模型 

分 类 号：P319[天文地球—固体地球物理学]