Mapping transition zone topography beneath China by migration of ScS reverberations.

The 410-km and 660-km boundaries in the mantle transition zone deflect in the presence of thermochemical heterogeneity. The western Pacific region is an ideal location to study the interaction of subducting slabs with transition zone discontinuities by modeling ScS reverberations recorded by hundreds of seismic stations in China and neighboring countries. We migrate ScS reverberation signals produced by 30 earthquakes in the Sea of Okhotsk, Philippine Sea, Sea of Japan, Myanmar, and Java to map topography on the 410-km and 660-km discontinuities beneath mainland China and its surrounding oceans. This technique is appraised by reproducing the analysis on spectral-element method seismograms generated for Earth models with variable transition zone topography and 3-D velocity heterogeneity. We present our ScS reverberation images and discuss their accuracy by identifying artifacts in the migrated SPECFEM waveforms.