[S-CG50] Structure, evolution and deformation of island arcs associated with subduction processes

[SCG50-11] Thermal structure of southwest Honshu arc estimated from seismic velocities

*Masahiro Ishikawa¹ (1.Graduate School of Environment and Information Sciences, Yokohama National University)

Keywords:crust, Thermal structure

The Philippine Sea Plate subducts at a relatively low angle in the Shikoku, Chugoku, and Kinki regions. What controls the thermal structure of the island arc in such a low-angle subduction zone? This study extracted temperature components from seismic wave velocities using seismic velocity data in the region of a constant Vp/Vs ratio from the three-dimensional seismic velocity structure by the National Research Institute for Earth Science and Disaster Resilience. This study estimated the temperature distribution, thermal gradient, depth of 300 °C, and brittle-ductile boundary depth. The temperature structure and brittle-ductile boundary depth distribution were obtained using seismic velocity data with a depth of 15 km in the Shikoku, Chugoku, and regions. The result shows that the 300 ° C depth was shallow along the Japan Median Tectonic Line and deepened on the north and south sides. The thermal structure is consistent with the depth of the lower limit of the seismogenic layer. In the Northeast Honshu Arc, the high-temperature region of the crust is distributed along the vicinity of the volcanic front (Ou Bockborne Range). On the other hand, in the Shikoku, Chugoku, and regions, the crust is the hottest near the Japan Median Tectonic Line than the Quaternary volcanic front. In the Shikoku, Chugoku, and regions, the effects of heat advection due to fluid dehydrated from the Philippine Sea slab may significantly control the thermal structure. The thermal structure was obtained for the Kyushu region using seismic velocity data with a depth of 15 km. The depth of 300°C and the brittle plastic boundary are shallow around Kagoshima and Oita. In Kyushu, where the Philippine Sea plate sinks at a high angle, the crustal temperature tends to be high overall. The feature is entirely different from the temperature structure of Shikoku, Chugoku, and regions where the Philippine Sea plate subducts at a relatively low angle.