Radial Anisotropy in East Asia From Multimode Surface Wave Tomography

Abstract

We present a model of radial anisotropy in the crust and upper mantle of East Asia from a combination of new group velocity measurements and previously published surface wave dispersion data sets. Our combined data set ranges 5–375 s period and contains dispersion data up to the fifth overtone. We directly relate the data to variations in isotropic and radially anisotropic shear wave crustal and mantle structure via surface wave ray theory applied to a prior 3-D reference model. Our isotropic S-velocity model shares high correlations with previous studies, including a model derived from a full waveform inversion methodology. The short period dispersion measurements in our data set allow us to resolve crustal structure without the need for crustal corrections, and as a result, our radial anisotropy model has significant differences with previous studies. We find strong positive radial anisotropy (ξ > 1) across the entire region in the middle to lower crust and uppermost mantle. We perform a cluster analysis and find high levels of radial anisotropy (ξ > 1.12) in the lithospheric mantle of the back-arc basin and in collisional belts, while low levels of radial anisotropy (ξ ∼ 1.04) are found in the mantle wedge of NE Japan and in the mantle upwelling under Mt. Baekdu. High radial anisotropy is found in the lower crust in regions that experienced continental rifting and lithospheric thinning, while the lowest crustal radial anisotropy is found in stable cratons.