The forearc seismic belt: A fluid pathway constraining down-dip megathrust earthquake rupture

Abstract

A portion of fluids subducted in an oceanic plate is thought to return to Earth's surface and has the potential to influence faulting during that migration. We used machine learning to detect and locate earthquakes in the northeast Japan forearc using data from a cabled ocean-bottom seismic network. That seismicity shows vertical distributions extending from the subducted plate to near the sea floor. The "forearc seismic belt" corresponds to the seismicity assumed to result from fluid supply from the underlying plate to the forearc and may also act to constrain the down-dip limit of megathrust rupture. The zone of high seismicity continues inland under metropolitan Tokyo, aligning with the Boso slow slip events and the eastern edge of the1923 Kanto earthquake, supporting forecasts of shallow damaging earthquakes.