摘要
基于近场加速度记录反演场地浅部速度结构,可为补充强震台站场地信息提供一种简便的途径,有利于记录的充分利用.本文详细推导了基于单一台站记录的P波地震图法,分析了其中的反演目标函数;通过数值模拟大量近场场地上的理论地震图,分析了场地覆盖层剪切波速、厚度等特征参数及震源持时对PS波与P波延时的影响,给出了地震记录的筛选原则;通过增加P波初到时刻径向分量与竖向分量幅值比函数作为反演目标函数,对单台地震图法进行改进;最后,利用汶川地震主震及余震记录,反演了武都强震台的场地波速结构,并与表面波法和钻孔法进行对比,结果表明,改进的单台地震图法搜索能力得到了增强,反演效率和精度得到显著提高.
Abstract
The P-wave seismogram method offers a fast and convenient approach to investigating the velocity structure at seismic stations using near-field strong aftershock records,thus maximizing the utility of these data.This method was thoroughly derived,and its inversion objective function was analyzed.Through numerical simulations of theoretical seismograms from multiple near-field sites,the impact of site characteristic parameters and seismic source duration on the delay between the PS-wave and P-wave was examined.The applicability of the seismic records was also assessed.To improve the single-station seismogram method,the amplitude ratio between the initial vertical and radial components at the first arrival of the P-wave was incorporated as an additional inversion objective function.The improved method was then applied to invert the S-wave velocity structure at the Wudu station using mainshock and aftershock records from the Wenchuan earthquake.Comparisons with the surface wave method and the borehole method demonstrate that the enhanced single-station seismogram method improved search capability,as well as inversion efficiency and accuracy.
维普
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