We model seismic and aseismic slip on the Japan megathrust in the area of the Mw9.0, 2011 Tohoku-Oki earthquake based on daily time series from 400 GPS stations of the GEONET network and campaign measurements of six sea floor displacements. The coseismic and postseismic slip distributions are inverted simultaneously using principal component analysis-based inversion method (PCAIM). Exploring a wide range of boundary conditions and regularization constraints, we found the coseismic slip distribution to be quite compact with a peak slip between 30 and 50 m near the trench. Our model shows deep afterslip fringing the downdip edge of the coseismic rupture but also a dominant zone of shallow afterslip. Afterslip over the first 279 days following the main shock represents about 40% of the coseismic moment. We compare the coseismic and postseismic models with an interseismic coupling model derived from inland and sea bottom measurements determined in a self-consistent manner. Assuming that seismic and aseismic slip had to match the long-term slip rate along the megathrust, the recurrence time of Mw9.0 earthquakes is estimated to 100-300 years, while historical and paleotsunami records suggest a return period more of the order of 1000 years. The discrepancy is smaller if the shallower portion of the megathrust is assumed to produce both aseismic slip, as the afterslip model suggests, and seismic slip during occasional large tsunamigenic earthquakes.
- 2011 Tohoku-Oki earthquake
- seismic cycle