On the construction of Moho reflected shear wave phases from ambient noise shear wave phases from ambient noise

Post-critical SmS reflections, shear waves reflected from the Moho at angles exceeding the critical angle, are frequently identified in ambient noise cross-correlation functions. Despite their consistent appearance across various arrays and studies, the physical origin and generation mechanisms of these SmS phases remain poorly understood. In this study, by investigating cross-correlation functions from a linear array, we show that SmS amplitudes strongly correlate with coastal ocean wave height, suggesting an oceanic origin. As microseismic energy propagates inland, crustal heterogeneities—such as Moho topography, surface relief, and variations in crustal velocities—facilitate the construction of SmS signals by altering the incident angles of the wavefields. These findings clarify key mechanisms underlying SmS excitation and propagation and support future applications of ambient noise body-wave analysis.