How mantle materials flow and how intraslab fabrics align in subduction zones are two essential issues for clarifying material recycling between Earth’s interior and surface. Investigating seismic anisotropy is one of a few viable technologies that can directly answer these questions. However, the detailed anisotropic structure of subduction zones is still unclear. Under a general hexagonal symmetry anisotropy assumption, we develop a tomographic method to determine a high-resolution three-dimensional (3D) P wave anisotropic model of the Japan subduction zone by inverting 1,184,018 travel time data of local and teleseismic events. As a result, the 3D anisotropic structure in and around the dipping Pacific slab is firstly revealed. Our results show that slab deformation plays an important role in both mantle flow and intraslab fabric, and the widely observed trench-parallel anisotropy in the forearc is related to the intraslab deformation during the outer-rise yielding of the subducting plate.

We study the three‐dimensional seismic attenuation (QP and QS) structure in the source area of the 2016 Kumamoto earthquake (M 7.3) by using 18,296 tP* and 29,668 tS* data from 742 local earthquakes recorded by a dense seismic network consisting of 112 stations deployed in Kyushu Island. Our results show that significant low‐Q (high‐attenuation) anomalies exist in the crust and mantle wedge beneath the volcanic front and back‐arc area, which reflect hot and wet zones caused by convective circulation in the mantle wedge and dehydration of the young Philippine Sea (PHS) slab. The 2016 Kumamoto earthquake occurred in a high‐Q and high‐velocity (high‐V) zone in the upper crust, which is surrounded and underlain by low‐Q and low‐V anomalies in the lower crust and upper mantle. These results suggest that the 2016 Kumamoto earthquake took place in a brittle seismogenic layer in the upper crust, but its rupture nucleation was affected by fluids and arc magma ascending from the mantle wedge. In addition, an obvious low‐Q zone is revealed in the fore‐arc mantle wedge, which reflects serpentinization of the fore‐arc mantle due to abundant fluids from the PHS slab dehydration.

We determine the first high‐resolution P and S wave attenuation (Q) tomography beneath the entire Japan Islands using a large number of high‐quality t∗ data collected from P and S wave velocity spectra of 4222 local shallow and intermediate‐depth earthquakes. The suboceanic earthquakes used in this study are relocated precisely using sP depth phases. Significant landward dipping high‐Q zones are revealed clearly, which reflect the subducting Pacific slab beneath Hokkaido and Tohoku, and the subducting Philippine Sea (PHS) slab beneath SW Japan. Prominent low‐Q zones are visible in the crust and mantle wedge beneath the active arc volcanoes in Hokkaido, Tohoku, and Kyushu, which reflect source zones of arc magmatism caused by fluids from the slab dehydration and corner flow in the mantle wedge. Our results also show that nonvolcanic low‐frequency earthquakes (LFEs) in SW Japan mainly occur in the transition zone between a narrow low‐Q belt and its adjacent high‐Q zones right above the flat segment of the PHS slab. This feature suggests that the nonvolcanic LFEs are caused by not only fluid‐affected slab interface but also specific conditions such as high pore pressure which is influenced by the overriding plate.