A new method for constraining crustal Vp/Vs ratio using P and S wave multiples

The ratio between compressional and shear wave speeds (Vp/Vs) in the Earth's crust is crucial for gaining a better understanding of its chemical composition and geological evolution history. Many studies employed H-κ stacking of receiver functions to estimate the crustal Vp/Vs ratio. However, the Vp/Vs ratio obtained from H-κ stacking can be biased due to lateral variations in crustal structures and/or incorrect absolute wave speed assumption. In this study, we propose a novel method to estimate the crustal Vp/Vs ratio using P and S wave multiples near receivers, that is the PpPmp (where m represents the Moho) and SsSms phases. The absolute arrival times of PpPmp and SsSms are sensitive to crustal thickness and wavespeeds, but the ratio of their arrival times is most sensitive to the crustal Vp/Vs ratio. We first verify the new method using synthetic tests on various crustal models. Synthetic results show that in the presence of lateral variation in crustal structure, the new method gives more accurate Vp/Vs ratios than the conventional H-κ stacking of receiver functions. We further validate the new method using field data recorded by the broadband station HYB in the eastern Dharwar Craton. Our data analysis involved preprocessing and manual selection of teleseismic events. Ultimately, the observed PpPmp and SsSms phases from 351 teleseismic events were used to calculate the Vp/Vs ratio beneath the HYB station, resulting in a value of 1.737±0.016. We find that this value is comparable to research results obtained by previous researchers using receiver function inversion (Zhou et al., 2000). Our new method for estimating crustal Vp/Vs ratio can potentially to applied to many other regions of tectonic importance.
This study is supported by National Natural Science Foundation of China (43/K22431006).