各向异性和倾斜界面介质中P波质点运动的理论模拟与应用

P波质点运动已经成为研究地震台站下方浅部地壳S波速度结构的一种重要手段.然而，现有研究主要基于水平层状各向同性介质的假设，对于各向异性和倾斜界面对P波质点运动的影响仍缺乏系统研究.本文通过理论模拟初步研究了各向异性和倾斜界面情况下的P波质点运动特征.模拟结果表明，各向异性和倾斜界面会使P波质点运动随反方位发生周期性变化，而且这种变化具有频率依赖性，反映了结构的垂向变化.四川盆地是研究青藏高原生长与物质外向逃逸的重要场所.本研究以盆地内部的宽频带流动地震台站S124为例，探讨利用P波质点运动研究浅部地壳各向异性和界面几何结构的可行性.研究结果显示，台站下方~4-5 km以浅的地壳具有明显各向异性（~20%），且其快轴方向（近东西向）与川中走滑断裂带走向一致.这表明研究区浅部地壳的变形模式可能主要受到断裂构造的控制.本研究的理论模拟和初步应用均表明，利用不同频率P波质点运动的反方位变化能够有效约束浅部地壳的各向异性和/或界面几何结构.

P-wave particle motions in anisotropic and dipping structures: theoretical simulation and practical application

P-wave particle motions have been widely utilized to study the S-wave velocity structure of the shallow crust beneath seismic stations. However, existing studies mostly assume horizontally layered isotropic media, overlooking the influence of dipping and anisotropic structures on P-wave particle motion. In this study, we present synthetic modeling of P-wave particle motions in dipping and anisotropic structures. The results show that dipping and anisotropic structures lead to periodic variations in P-wave particle motions with back-azimuth. The periodic variations are also dependent on frequency, reflecting the depth-dependent variation in structures. The Sichuan Basin is a key area to study the growth and outward escape of the Tibetan Plateau. We apply the P-wave particle motion method to one station (S124) within the basin to evaluate its potential to investigate the dipping and anisotropic structures of the shallow crust. The results show that the shallow crust, to a depth of approximately 4 to 5 km beneath the station, exhibits approximately 20% anisotropy, with the fast axis direction aligning with the strike of Central Sichuan strike-slip fault belts. These findings indicate that faulting may control the deformation at shallow crustal depths in the study area. Both synthetic tests and real data analyses demonstrate the effectiveness of using the back-azimuth dependence of multi-frequency P-wave particle motions to constrain the anisotropic and dipping structures of the shallow crust.