首都圈地区远震基底PS波分裂研究

Tele-seismic PS-wave splitting from the basement in the Capital area of China

远震PS波的一个重要优势是其携带台站下方介质的各向异性信息.本文基于首都圈数字地震台网2002-2003年记录的高精度远震波形资料,从基底PS转换波入手,采用三分量PS波分裂偏振分析方法,获取各个台站下方来自基底的PS波分裂参数,包括快波偏振方向和快、慢波的时间延迟等,分析台站下方浅部地壳介质的各向异性特征.几个台站的研究结果显示,该方法保持了原始波场的信息,可以用来分析PS波分裂特征;短周期台站记录的远震来自基底的PS波具有干扰少、信噪比高的特点,存在分裂现象,各台站快慢波时差超出我们的预期值,平均在0.1-0.2 s左右.此研究可与横波分裂相对比,对于认识地壳各向异性及其内部的应力状态,分析其构造及地震活动现象有较大的意义.

An Important advantage of tele-seismic PS-waves is carrying the anisotropy information of media beneath seismic stations. This paper uses the analysis method of three-component PS- wave splitting to analyze the basement PS-waves based on the high-precision tele-seismic data of Capital Area Seismic Network （CASN） from 2002 to 2003. The purpose is to acquire the PS-wave splitting parameters beneath the seismic stations, including polarization of fast PS-waves and the time delays of fast and slow PS-waves, and to reveal the shallow crust anisotropy beneath the seismic stations. The results show that this method preserves the original information of the wave field, which allows us to analyze the features of PS-wave splitting. The tele-seismic PS-waves from the basement recorded by short period stations have the advantage of less noise and higher SNR, and have splitting phenomena commonly. Besides we find the time delay of fast and slow PS-waves is beyond our expectation, which has average values of time delay 0. 1-0.2 s. This research can be compared with shear-wave splitting, which would help recognize anisotropy and stress state of crust and study tectonics and seismic activity.