Influence of shear wave velocity heterogeneity on SH-wave reverberation imaging of the mantle transition zone

SUMMARY Long-period (T > 10 s) shear wave reflections between the surface and reflecting boundaries below seismic stations are useful for studying phase transitions in mantle transition zone (MTZ) but shear-velocity heterogeneity finite-frequency effects complicate interpretation of waveform stacks. We follow up on a recent study by Shearer & Buehler (hereafter SB19) top-side reflection Ssds as probe mapping depths 410-km 660-km discontinuities beneath USArray. Like SB19, we observe that recorded Ss410s-S Ss660s-S traveltime differences longer at western United States than central-eastern States. The about 40–50 km deeper if transformed to depth using common-reflection point (CRP) approach based 1-D model (PREM our case). However, east-to-west deepening MTZ disappears CRP image account 3-D velocity variations according global tomography. In addition, from spectral-element method synthetics, find ray theory overpredicts delays reverberations. Undulations underestimated when their wavelengths smaller Fresnel zones reverberations MTZ. Therefore, modelling layering upper must be reference structures accurate calculations reverberation traveltimes.