High-resolution Model of the Crust and Uppermost Mantle beneath the East Sea Inferred from a Joint Inversion of Waveform Fits and Ambient Noise Dispersion

While small-scale geophysical exploration surveys have been able to elucidate the nature of the shallow crust in certain regions of the East Sea (Sea of Japan), large-scale tomographic studies have been hampered by a lack of data able uniformly cover the region. In this study, we combine linear constraints derived from ~13,000 nonlinear three-component waveform fits with ~16,000 short-period Rayleigh and Love group velocity dispersion curves measured from 3.5 years of continuous seismic ambient noise. The combination of these two datasets increases our ability to resolve structures in the crust and uppermost mantle throughout the entire East Sea. Our radially anisotropic model is able to image the subducting Philippine and Pacific plates as high-velocity anomalies in accordance with previously published studies. We find high positive radial anisotropy anomalies (VSH2/VSV2 > 1) above the subducting slabs along the southwestern margin of the East Sea, which may be due to horizontally flowing mantle material in the mantle wedge. More intriguingly, our model shows a ring of high-velocity anomalies along the margins of the East Sea just below the Moho. Along the southern margin, the high-velocity anomalies and high positive radial anisotropy may indicate the remnants of pooled magma or horizontally deformed volcanic sills in the shallow mantle lithosphere resulting from the rifting processes that formed the East Sea. On the northern margin, however, the high-velocity anomalies appear in conjunction with weak or slightly negative radial anisotropy, which may indicate the presence of vertical dykes in rifted continental crust.