1556年华县大地震地震动场模拟

Strong motion simulation of the 1556 Great Huaxian earthquake

1556年华县地震是中国历史地震中人口伤亡最多、灾害最为严重的大地震。本文利用渭河盆地三维速度结构模型和1556年华县地震活动断裂研究成果,采用谱元法模拟了华县地震中渭河盆地0.02-0.5Hz地震波的传播过程。基于峰值速度和盆地典型剖面速度时程分析,讨论了盆地对地震动的放大作用。研究表明,渭河盆地的深厚土层对于4s以上的地震动有着明显的放大作用,强烈地震动主要位于断层北侧的第四系覆盖层厚度超过900m的区域。当破裂方向指向渭河盆地中第四系覆盖层大于1000 m的深凹陷时,在破裂方向性效应和盆地的边缘效应的共同作用下,导致大量的能量被其捕捉,从而引起及其强烈的地震动和长持时高幅值面波,这是渭河盆地地震危险性分析中需要特别注意的问题。

The 1556 Great Huaxian earthquake was the most deadly and disastrous earthquake in the history of China.Based on the three-dimensional velocity structure model of Weihe basin,and the research results of the active fault of this earthquake,the propagations of seismic waves in frequency band of 0.02-0.5 Hz in the Weihe basin during 1556 Huaxian earthquake are simulated by using the spectral element method.Based on the distribution of PGV and velocity time-history analysis of typical profiles,the amplification effects of the basin are analyzed.The study shows that the deep soil layers of Weihe basin have an obvious amplification effects on ground motion above 4 s,and strong ground motions are mainly located on north side of the fault in Weihe basin where the Quaternary thickness exceeds 900 m.When the fault rupture to deep sag with Quaternary thickness exceeds 1000 m,a large amount of energies were captured in it,result of extremely amplitude strong ground motion and long duration surface wave due to both the rupture directivity effect and the basin edge effect.This should be paid special attention in seismic hazard analysis in Weihe basin.