震源机制参数对模拟地震动场速度脉冲的影响

Effect of focal mechanism parameters on velocity pulses of simulated ground motion field

近断层区域脉冲型地震动对于大跨度工程结构地震响应具有重要影响,然而大震近场记录的匮乏使得探究脉冲型地震动的特征较为困难.本文借助基于运动学震源模型的地震动合成方法,合成不同震源机制参数情况下的近场地震动场.采取基于能量的速度脉冲识别方法,提取合成地震动场中的速度脉冲并计算脉冲周期和幅值,分析震源机制参数对速度脉冲空间分布及脉冲特征参数的影响规律.研究表明:断层走向变化主要影响脉冲型地震动的方位;倾角和滑动角主要影响脉冲型地震动的数量和分布方位;脉冲型地震动更易出现在与断层走向斜交的方向上,在垂直断层走向方向上脉冲型地震动分布相对较少;走向对脉冲特征参数影响很大;相对于脉冲周期,断层倾角对脉冲幅值影响更显著;倾滑断层引起的垂直分量脉冲周期明显大于其他震源机制情况.

The pulse-like properties of ground motions are of great influence on the seismic response of long-span structures in the near-fault region field. However,due to the insufficiency of nearfault field records for large earthquakes,it is difficult to explore the effect of focal mechanism on pulse-like ground motions. Therefore,a deterministic physics-based method based on kinematic model is used to simulate near-field ground motions in the near field for various focal mechanism scenarios in this paper. The pulse-like ground motions are identified by the energy-based method,and then the periods and the amplitudes of velocity pulses are extracted for each scenario. The effects of focal mechanism parameters on the spatial distribution of pulse-like ground motions and pulse characteristic parameters are investigated. The results show that the changed fault strike mostly affects the distribution directions of pulse-like ground motions,the dip and the rake of fault mainly affect the quantity and the distribution directions of pulse-like ground motions. The pulse-like ground motions are more likely to appear in the directions obliquely intersected with the fault strike and relatively less in the directions perpendicular to the fault strike.The effects of fault dip on the spatial distribution of pulse-like ground motions between the strike-slip fault scenarios and the dipslip fault scenarios show significant differences. Focal mechanism parameters can also affect the parameters of velocity pulses that appear in the fixed position. The fault strike can greatly affect the pulse parameters,both including for the period and the amplitude.Compared with the pulse period,the influence of fault dip on pulse amplitude is more significant. The pulse periods of fault-normal components for dip-slip fault are generally higher. The pulse period and the pulse amplitude commonly describe the pulse energy of pulse. For the parallel component of the strike-slip fault,the pulse energy along the fault strike direction is greater than that in other directions. Among all scenarios,the pulse energy of normal components for dip-slip fault is generally higher.