利用SPAC法估算地壳S波速度结构

Application of SPAC method to estimate the crustal S-wave velocity structure

S波速度结构能够反映地球介质的物性差异，是地壳内低速区结构特征判别的重要依据．本文尝试利用空间自相关法（SPAC法）从地震台站微动信号的垂直分量中提取瑞利波相速度频散曲线，通过对频散曲线的反演获得地下介质的S波速度结构．以国家数字测震台网8个宽频带地震台站的实测微动数据为例，采用SPAC方法获得了首都圈地区北京附近约30km深度范围内的一维S波速度结构．结果表明，该区结晶基底埋深较浅约2km；分别在5～8km和12～16km深处发育S波低速层；8km和20km处是S波速度差异较大的速度分界面．这一结果与以往地震学及人工地震探测结果较为吻合，表明SPAC法估算地壳s波速度结构是可行、有效的．

S-wave velocity structure can reflect the differences of physical properties of Earth media, and is the important basis of identifying the structural characteristics of the low velocity zone. This article attempts to use spatial autocorrelation method （SPAC method） to extract Rayleigh-wave phase velocity dispersion curves from the vertical component of the seismic stations＇ microtremors, and through the inversion of dispersion curve, acquires the S-wave velocity structure. Taking 8 broadband seismic stations＇ actual measurement from China National Seismic Network for example, we acquired the one-dimensional S-wave velocity structure of 30 km depth range using this method in the Capital area near Beijing. The inversion result shows that the crystalline basement of this region is about 2 km deep; there is S wave low-velocity layer at 5-8 km and 12-16 km depth; the depth 8 km and 20 km stands for the speed interface of S- wave that has a big speed difference. This result has good consistency with seismology and artificial seismic exploration results, which illustrates that estimating the crustal S-wave velocity structure using spatial autocorrelation method is feasible and effective.