利用纯S波输入研究地震台站下方的横波速度结构

震中距在50°左右的深源远震,直达波S波震相波列可以与其他震相波列分离. 在层状介质中,本文通过传播矩阵方法得到由S波从台下底层输入获得地面理论地震图的新方法,并由此拟合了河北省两个地震台短周期S波记录,获得台站下方横波速度结构. 结果表明,红山台下13km和24km左右有S波低速层存在,地壳厚度为33.km;涉县台下18km和30km左右有S波低速层存在. 红山台下S波差异显著的2个低速层夹持的高速层、较薄地壳及上地幔顶部低S波速度结构,与166年邢台大地震有关. 考虑到S波速度对部分熔融体的敏感性,认为地壳S波速度结构可作为揭示强震深部背景的依据之一.

A STUDY ON TRANSVERSAL WAVE VELOCITY STRUCTURE UNDER SEISMIC STATION BY INPUTTING PURE S WAVE

The direct S wave phase of deep teleseisms with epicentral distance of about 50° can be separated from other seismic phases. Based on the propagation matrix method, a new method is proposed for getting surface synthetic seismogram from the S wave input beneath a sismostation. The data of S wave recorded at two short-period seismostations in Hebei province are fitted with this method. The results show that there are two layers of low velocity for S wave, the depths of which are about 13km and 24km beneath Hongshan station. There are also two layers of low velocity at 18km and 30km beneath shexian station. The high velocity interlayer exists between the two low-velocity layer. The thinner crust and the S wave velocity structure above the upper mantle may be related to the Xingtai great earthquake occurred in 1966. Considering the sensitivity of S wave velocity to partially melting, we believe that S wave velocity structure of the crust can be used to reveal the deep background of strong earthquakes. Waveform fitting of short-period S wave expands the application of waveform information on seismograms, and provides a new method for the acquirement of transversal velocity structure directly under a station.