Geoelectrical evidence of fluid controlling slow and regular earthquakes along a plate interface

Shallow subducting plate interfaces, as sites of both destructive and “slow” earthquakes, resulting from rapid and slower fault slips, respectively, present a major scientific and disaster mitigation challenge. Although understanding the different slip mechanisms and their spatial relationships is critical, the role of a key factor, pore fluids, is understudied. Here we present clear observational evidence from Hyuga-nada, southwestern Japan, that the pore-fluid distribution correlates with fault rupture behavior. A 3D electrical resistivity model derived from marine magnetotelluric survey data reveals distinct resistive and conductive anomalies along the plate interface that reflect areas of scarce pore fluid and high concentration area of pore fluids sourced from subducting seamounts (Kyushu–Palau Ridge), respectively. The wet area corresponds to the slow slip area whereas dry and the transition areas correspond to areas of fast fault slip. These findings highlight the influence of the pore-fluid distribution on fault processes and underscore its importance in earthquake and tsunami risk assessments.