Detection of a hidden Boso slow slip event immediately after the 2011 M w 9.0 Tohoku‐Oki earthquake, Japan

Utilizing a cross‐correlation detector technique, we discovered an increase in swarm‐like seismicity within the source area of the Boso slow slip events (SSEs) immediately after the 2011 Tohoku‐Oki earthquake. The epicentral distribution of the detected seismicity was similar to that of previously recognized Boso SSEs. In addition, small repeating earthquakes were identified within this seismic swarm sequence. These seismic observations indicate that a hidden SSE occurred along the top surface of the subducting Philippine Sea plate immediately after the Tohoku‐Oki earthquake. We propose that external stress transfer by the coseismic slip of the Tohoku‐Oki earthquake and the following afterslip could have led to the occurrence of the newly detected Boso SSE. In contrast to previous work, we demonstrate that the recurrence interval of the Boso SSEs has not shortened over time but has shown a more complex evolution as a result of external stress perturbations imposed by the Tohoku‐Oki earthquake. A hidden Boso SSE was induced immediately after the Tohoku‐Oki earthquake Higher slip rate and more rapid migration of the March 2011 Boso SSE than usual The recurrence interval of the Boso SSEs has shown a more complex evolution