Improved geometry of the subducting Philippine Sea plate beneath the Suruga Trough

Abstract

The Philippine Sea (PHS) plate subducts beneath the Eurasian plate at the Suruga Trough where megathrust earthquakes have repeatedly occurred. We used data from permanent seismic stations on land and temporary seismic stations beneath Suruga Bay to resolve the seismic velocity structure from the surface to 40–60 km depth beneath the Tokai region. The Median Tectonic line runs through the Tokai region and forms a boundary between high-V and low-V zones. We constrained the configuration of the subducting PHS plate using results from seismic tomography, hypocentral distribution of microseismicity, and low-angle thrust-type earthquakes. The oceanic crust of the PHS plate is characterized by low-V and high-Vp/Vs values. Events with thrust-type focal mechanisms are expected at the plate boundary. We constructed the geometry of the surface of the subducting PHS plate using this information. This geometry is also consistent with the results of receiver functions. The surface of the PHS plate is slightly (approximately 6–10 km) shallower than estimated from previous studies, especially in the zone extending from the Suruga Trough to a depth of 20 km. The data combination of permanent land and temporary OBS station with rays crossing the plate boundary clarify the plate configuration at the shallow subduction zone.