一种改进的适应于倾斜Moho面的H-κ-θ叠加方法及应用

地壳厚度、波速比或泊松比是研究地壳结构和性质的基本地震学参数，对于研究地壳组分特征及构造演化具有重要意义.经典H-κ叠加方法是利用远震接收函数资料求取台站下方地壳厚度和波速比最为简便高效的方法.但该方法隐含着Moho面是水平界面的假设条件，意味着Ps转换波及后续多次波相对P波的走时主要取决于地壳厚度和纵横波速度，而忽略了界面产状的影响.理论模拟表明，如果不考虑Moho面的产状，特别是在Moho面倾角较大的情况下，利用经典H-κ叠加方法得到的地壳厚度和波速比会偏离实际模型，尤其会造成波速比的过高估计，从而影响到对地壳结构和性质的认知.为了解决Moho面倾斜条件下的地壳厚度和波速比求取问题，本文推导了界面倾斜条件下Ps转换波与后续多次波相对于直达P波的理论到时公式；基于经典H-κ叠加方法的思想，提出了一种可以同步求取地壳厚度-波速比-Moho面倾角的H-κ-θ叠加方法.通过理论模型测试，验证了该方法具备较高的稳定性和可靠性，并将此方法应用于青藏高原南部Hi-CLIMB台阵资料，显示出较好的应用潜力.

An improved H-κ-θ stacking method to determine the crustal thickness and bulk vP/vS ratios in the case of a slant Moho interface

Crustal thickness and v_P/v_S ratio (or Poisson's ratio) are the key seismological parameters for studying the crustal composition and properties. The H-κ stacking method is widely used as one of the most powerful techniques to determine the two parameters beneath a seismic station using teleseismic P-wave receiver functions. However, the H-κ stacking method assumes the Moho interface is flat, and thus the arrival times of converted Ps waves and subsequent multiples relative to the direct P-wave depend mainly on the crustal thickness and P-and S-wave velocities. The synthetic test shows that the crustal thickness and v_P/v_S ratios obtained by the H-κ stacking method would greatly deviate from the real model when the Moho interface is slant, and this deviation increases with the increasing dip angle of the Moho interface. In particular, this deviation will lead to the overestimation of v_P/v_S ratios, and eventually mislead the interpretation of the crustal structure and properties. In this study, the formulas of the theoretical arrival times of converted Ps waves and multiples between the slant Moho interface and the ground surface are derived, and then an improved H-κ-θ stacking method is developed to determine the crustal thickness, bulk v_P/v_S ratios and dip angle of the Moho interface (H-κ-θ) simultaneously based on the idea of the H-κ stacking method. The synthetic tests validate the good stability and reliability of the improved H-κ-θ stacking method. Applying the improved method to the Hi-CLIMB array data in southern Tibet further shows that the H-κ-θ stacking method has the good practicability for real seismic data.