Age of the Subducting Philippine Sea Slab and Mechanism of Low‐Frequency Earthquakes

Abstract

AbstractNonvolcanic low‐frequency earthquakes (LFEs) usually occur in young and warm subduction zones under condition of near‐lithostatic pore fluid pressure. However, the relation between the LFEs and the subducting slab age has never been documented so far. Here we estimate the lithospheric age of the subducting Philippine Sea (PHS) slab beneath the Nankai arc by linking seismic tomography and a plate reconstruction model. Our results show that the LFEs in SW Japan take place in young parts (~17–26 Myr) of the PHS slab. However, no LFE occurs beneath the Kii channel where the PHS slab is very young (~15 Myr) and thin (~29 km), forming an LFE gap there. According to the present results and previous works, we think that the LFE gap at the Kii channel is caused by joint effects of several factors, including the youngest slab age, high temperature, low fluid content, high permeability of the overlying plate, a slab tear, and hot upwelling flow below the PHS slab.