Source process with heterogeneous rupture velocity for the 2011 Tohoku-Oki earthquake based on 1-Hz GPS data

A rupture model with varying rupture front expansion velocity for the March 11, 2011, Tohoku-Oki earthquake was obtained by the joint inversion of high-rate Global Positioning System (GPS) data and ocean bottom GPS/acoustic (OB-GPS) data. The inverted rupture velocity with a complex distribution gradually increases near the hypocenter and shows rapid rupture expansion at the shallowest part of the fault. The entire rupture process, which lasted 160 s, can be divided into three energy release stages, based on the moment rate function. The preferred slip model, showing a compatible relationship with aftershocks, has a primary asperity concentrated from the hypocenter to the trench and a small asperity located on the southern fault. Source time functions for subfaults and temporal rupture images suggest that repeated slips occurred in the primary rupture, which is consistent with that from seismic waveforms. Our estimated maximum slip and total seismic moment are similar to 65 m and 4.2 x 10(22) Nm (Mw 9.0), respectively. The large slip, stress drop, and rupture velocity are all concentrated at shallow depths, which indicates that the shallow part of the fault radiated high-frequency as well as low-frequency seismic waves.