垂直和倾斜断层围陷波的谱元法数值模拟及其波场特征对比

Fault zone trapped waves( F ZTWs) m ainly travel along the fractured fault zone( F Z)which is of low velocity and high attenuation. FZTWs often carry significant information about a fault  s internal structure,so it is important to understand their wave field characteristics for FZ structure inversion. Most previous simulations are based on vertical faults,while in this paper we implement the FZTW simulations on vertical or inclined faults and compare their wave fields in both time and frequency domains. The results show that the existence of fault zone and inclined angle of fault can significantly influence the features of waves near faults. In amplitude,a fault zone can generate a larger amplitude of waves. The velocity contrast between two walls of fault may lead to amplification of amplitudes in the low velocity fault wall. In frequency,a fault zone tends to influence the waves in the low frequency range. In a pattern of particle polarization of FZTWs,it tends to be single direction for vertical faults but fork to multiple directions for inclined faults,which might provide a new way to study the fault zone with FZTWs. These conclusions may be valuable for FZ structure inversion,and will enhance the knowledge on near-fault strong ground motions.     

垂直和倾斜断层围陷波的谱元法数值模拟及其波场特征对比

低速断层破碎带内传播的断层围陷波是断层内部信息的重要载体,研究其波场特征是反,演断层内部结构的关键。前人对围陷波的模拟主要针对垂直断层,但实际断层大部分是倾斜的。本文利用谱元法数值模拟地震波在垂直和倾斜断层区域的传播,并分别单独改变断层破碎带或断层两盘速度差异等参数,对比分析地震动在时域和频域发生的变化,研究这些参数对波场特征的影响。对比研究表明,当存在一定宽度的低速破碎带时,倾斜断层对近断层区域波场的影响和垂直断层相比在幅值分布上有比较显著的差异,尤其是当断层两盘同时还存在速度差异时;在倾斜和垂直断层破碎带上方,均能产生断层围陷波,其幅值特征差异不大,但在跨断层平面上的质点极化方式可能会存在差异:垂直断层围陷波质点极化方向表现为单一,而倾斜断层可能会出现多个方向。这些模拟结果有助于反演真实断层破碎带结构,也能够加深对近断层的强地面运动特征的认识。