Abstract
Seismic anisotropy provides important information on the structure and geodynamics of the Earth. The forearc mantle wedge in subduction zones mainly exhibits trench-parallel azimuthal anisotropy globally, which is inconsistent with the model of olivine a axis aligning with the slab-driven corner flow. Its formation mechanism is currently unclear. Here we present high-resolution 3-D P wave anisotropic tomography of the Tohoku subduction zone. We suggest that ductile deformation of the forearc lithospheric mantle of the overriding plate induces the trench-parallel azimuthal anisotropy and positive radial anisotropy (i.e., horizontal velocity > vertical velocity) in Tohoku. Our results provide the first seismic anisotropic evidence for the slab-mantle decoupling at a common depth of ~70 km. On the basis of the high-resolution seismic images, we propose a geodynamic model suggesting that the forearc mantle wedge anisotropy is produced via ductile deformation of dry olivine or hydrous antigorite lithospheric mantle, which accords well with the trench-parallel shear wave splitting measurements dominant in subduction zones globally.
Original language | English |
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Pages (from-to) | 7013-7027 |
Number of pages | 15 |
Journal | Journal of Geophysical Research: Solid Earth |
Volume | 124 |
Issue number | 7 |
DOIs | |
Publication status | Published - 2019 |
Keywords
- lithospheric deformation
- seismic anisotropy
- subduction zone
- tomography
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science