Imaging the spatiotemporal evolution of a slow slip event near the Boso Peninsula, central Japan

Abstract:

Continuous GPS measurements have identified numerous slow slip events (SSEs), but our knowledge of the spatiotemporal evolution of SSEs remains limited. For example, the detailed spatiotemporal correlation between slow slip and its associated seismic activity has not been well resolved, and we have limited knowledge of SSE nucleation. Thus, elucidating the detailed spatiotemporal evolution of SSEs may help constrain the physics of SSEs and their associated seismic activity. In this study, we use a modified version of the Network Inversion Filter (NIF) to investigate the detailed spatiotemporal evolution of SSEs including the nucleation and spatiotemporal correlations with seismicity.

We focus on a SSE that occurred near the Boso Peninsula, in central Japan, from December 2013 to January 2014. We apply the modified NIF to GPS time series to estimate the spatiotemporal evolution of daily cumulative slip and slip rate on the subducting Philippine Sea plate. We find that the evolution of the SSE and its associated seismicity is divided into two distinct phases. Slip initially accelerated slowly with low slip rates, low propagation speeds, and no accompanying seismicity during the early phase, and then accelerated more rapidly with higher slip rates, a higher propagation speed, and local earthquake swarm activity during the later phase. The seismicity was highly correlated in space and time with slip rate, suggesting that the swarm activity was triggered by stress loading due to the slow slip. The transition from the slow to faster phase shares some similarities with the nucleation of megathrust earthquakes inferred from foreshock activities, suggesting that SSEs may provide insights into the nucleation of large earthquakes.