Crust-mantle decoupling revealed by seismic velocity anisotropy beneath Syowa Station, Antarctica

Abstract

We analyzed shear wave splittings in the crust beneath Syowa Station, using Moho converted Ps waves. Three set of receiver functions and stacked receiver functions from Tonga events are analyzed. Results are interpreted by conbining with seismic anisotropy in the mantle, which have been revealed by SKS splitting. The observed fast polarized direction of crustal shear wave splitting shows N50°W, which is nearly perpendicular to that in the mantle (N49°E). Delay times of crustal anisotropy reach 0.5s. Although part of crustal anisotropy can be caused by the deformation due to Gondwana's break up, the most plausible explanation of crust-mantle decoupled anisotropy is related to the collisional deformation 500 Ma. If delamination between the crust and the mantle occurred in a former stage of metamorphism with subsequent crustal extrusion and mantle subduction, then observed seismic anisotropy in both the crust and the mantle can be explained.