Relationship between tectonic tremors and 3-D distributions of thermal structure and dehydration in the Alaska subduction zone.

The Alaska subduction zone is characterized by a subducting oceanic plateau, which is referred to as the Yakutat terrane. Tectonic tremors occur in this zone, and there are few volcanoes above the subducted Yakutat terrane. In this study, we performed a 3-D numerical simulation of a thermal structure associated with the simultaneous subduction of the Yakutat terrane and Pacific plate to elucidate the mechanism of tectonic tremors, which typically involve the presence of water.

3-D thermal regime and dehydration processes around the regions of slow earthquakes along the Ryukyu Trench.

Several interplate seismic events, such as short-term slow slip events (S-SSEs) and low-frequency earthquakes (LFEs), have been identified in the Ryukyu Trench, southwestern Japan. As one of the specific characteristics of this seismicity, the depths at which S-SSEs occur at the plate interface beneath Okinawa Island are approximately 5-10 km shallower than those beneath the Yaeyama Islands. To elucidate the cause of this difference in depth, we constructed a three-dimensional, Cartesian thermomechanical subduction model and applied the subduction history of the Philippine Sea (PHS) plate in the model region.

Contrasting volcano spacing along SW Japan arc caused by difference in age of subducting lithosphere.

The SW Japan arc built by subduction of the Philippine Sea (PHS) plate exhibits uneven distribution of volcanoes: thirteen Quaternary composite volcanoes form in the western half of this arc, Kyushu Island, while only two in the eastern half, Chugoku district. Reconstruction of the PHS plate back to 14 Ma, together with examinations based on thermal structure models constrained by high-density heat flow data and a petrological model for dehydration reactions suggest that fluids are discharged actively at depths of 90-100 km in the hydrous layer at the top of the old (> 50 Ma), hence, cold lithosphere sinking beneath Kyushu Island. In contrast, the young (15-25 Ma) oceanic crust downgoing beneath Chugoku district releases fluids largely at shallower depths, i.