Subslab heterogeneity and geodynamics of Japan subduction zone

SUMMARY High-resolution P-wave velocity tomography of the Japan subduction zone down to 700 km depth is determined by conducting a joint inversion of arrival-time data of local earthquakes and teleseismic events, which were recorded at land-based Hi-net seismic stations and seafloor S-net stations. Our inversion results show the high-velocity subducting Pacific slab and low-velocity zones in the mantle wedge beneath active arc volcanoes. Subslab low-velocity anomalies (SLVAs) are revealed in the mantle below the Pacific slab, which may reflect hot and wet mantle upwelling derived from return flow associated with the slab deep subduction. The SLVAs at depths of ~150–260 km exhibit a bimodal distribution, where interplate slow earthquakes occur. There is a SLVA gap below the main shock hypocentre and rupture zone of the great 2011 Tohoku-oki earthquake (Mw 9.0). The SLVAs may influence the megathrust segmentation by their buoyancy, heat and melt, and so affect the generation of megathrust and intraslab earthquakes. These results shed new light on the structural heterogeneity and mantle dynamics of the Japan subduction zone.