Recovery of the recurrence interval of Boso slow slip events in Japan

Abstract

We present the spatiotemporal evolution of the Boso slow slip event with a moment of 20 × 1018 N m that occurred in June 2018; such events, which have a duration of 1–2 weeks, have repeatedly occurred off the Boso peninsula, east Japan. The initial rupture of the 2018 event started off central Boso peninsula and the center of the rupture area moved southward over time, as was observed in previous events. The moment and the slip rate of the 2018 event are the largest among the previous Boso slow slip events. The recurrence interval of major Boso slow slip events has changed from 4 to 6 years before the 2011 Tohoku earthquake to intervals of 0.6, 2.2 and then 4.4 years after the Tohoku earthquake. It has taken 7 years for the recurrence interval of the major Boso slow slip events to roughly recover to that before the Tohoku earthquake. The relationship between the cumulative moment and recurrence time indicates a slip-predictable model rather than a time-predictable model before the Tohoku earthquake. If a slip-predictable model holds after the Tohoku earthquake, there was possibly an increase in the moment release rate after the 2011 Tohoku earthquake. Boso slow slip events are changing the stress state in favor of the occurrence of an interplate earthquake along the Sagami trough, Japan.