Depth-varying azimuthal anisotropy in the Tohoku subduction channel

• Published in: Earth and planetary science letters Vol. 473; pp. 33 - 43
• Main Authors: Liu, Xin, Zhao, Dapeng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2017
• Subjects: azimuthal anisotropy; megathrust earthquakes; subduction; Tohoku; tomography; Tohoku; subduction; azimuthal anisotropy; tomography; megathrust earthquakes
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2017.05.034

We determine a detailed 3-D model of azimuthal anisotropy tomography of the Tohoku subduction zone from the Japan Trench outer-rise to the back-arc near the Japan Sea coast, using a large number of high-quality P and S wave arrival-time data of local earthquakes recorded by the dense seismic network on the Japan Islands. Depth-varying seismic azimuthal anisotropy is revealed in the Tohoku subduction channel. The shallow portion of the Tohoku megathrust zone (<30 km depth) generally exhibits trench-normal fast-velocity directions (FVDs) except for the source area of the 2011 Tohoku-oki earthquake (Mw 9.0) where the FVD is nearly trench-parallel, whereas the deeper portion of the megathrust zone (at depths of ∼30–50 km) mainly exhibits trench-parallel FVDs. Trench-normal FVDs are revealed in the mantle wedge beneath the volcanic front and the back-arc. The Pacific plate mainly exhibits trench-parallel FVDs, except for the top portion of the subducting Pacific slab where visible trench-normal FVDs are revealed. A qualitative tectonic model is proposed to interpret such anisotropic features, suggesting transposition of earlier fabrics in the oceanic lithosphere into subduction-induced new structures in the subduction channel. •3-D VP and VS azimuthal anisotropies beneath NE Japan are investigated.•Depth-varying azimuthal anisotropy is revealed in the subduction channel.•Earlier fabrics in the Pacific plate are altered by the subduction processes.