断层破裂速度对地震动影响的离散波数有限元法模拟

地震断层的破裂速度是断层破裂过程中的一个重要参数，它对近场地震动及其空间分布，特别是近场地震动的方向性特征有着重要的影响．为从理论上分析断层不同破裂速度对地震动方向性效应的影响，根据设定地震和根据统计关系得到的震源参数，采用离散波数有限元方法数值模拟不同破裂速度下地表观测点的地震动时程，分析地震动的峰值、反应谱和持时3个基本参数及其空间分布特征．研究表明：在地震马赫数为0．700～0．925的破裂速度范围内，断层破裂值均会使地震动及其分布呈现明显的方向性特征；断层破裂前方的地震动峰值和反应谱值大于破裂后方的地震动值，地震动持时则相反；在断层破裂方向的末端一定距离内存在一个典型的区域，在此区域内的地震动显著受到方向性的影响和控制，其地震动峰值和反应谱值显著高于其他区域，而持时则低于其他区域．总之，破裂速度对地震动及其分布的方向性特征有重要影响，随着破裂速度逐渐接近于剪切波速，地震动的方向性特征也越来越明显．

Modeling the Effect of Fault Rupture Velocity on Ground Motion by Discrete Wavenumber Finite Element Method

Rupture velocity is a key parameter in controlling the fault rupture process, and it is also an important factor affecting the directivity of ground motion and its distribution. The effect of rupture velocity on directivity was studied by using simulated seismic ground motions of a vertical strike-slip fault. Based on a scenario earthquake with kinematic fault parameters, a discrete wavenumber finite element method was adopted to calculate the ground motion in horizontal layered half space. Analyses of synthetic peak ground motion, response spectra and duration indicate that within the seismic Mach number between 0.700---0.925, there are distinct directivity effects on the ground mo- tion parameters and their distribution field. As expected, the peak ground motion and response spectra in the forward direction are higher than those in the backward direction; a directivity-distinctly-affected area appears in the forward direction, where ground motions have relative larger amplitude and smaller duration than those in the vicinity areas; the closer the rupture velocity to the shear wave velocity, the more distinct the directivity gets.