Source Process of the 2011 Off the Pacific Coast of Tohoku Earthquake
The kinematic source process of the 2011 Off the Pacific Coast of Tohoku earthquake is studied using strong motion data both in low- and high-frequency ranges. The slip distribution is estimated by the waveform inversion analysis using velocity waveforms in the frequency range from 0.01 to 0.125 Hz at strong motion stations along the Pacific coast. The strong motion generation area (SMGA) is estimated by the strong ground motion simulation in 0.1–10 Hz using the empirical Green’s function method. The slip distribution is characterized by a large asperity with peak slip of 48 m which is imaged in the shallower portion of the source fault near the Japan Trench. Four SMGAs are identified in the deeper portion of the source fault. Unlike the past M7–8 subduction-zone plate-boundary events, the SMGAs and the asperity seem to be complementary in space. But the rupture time of each SMGA matches the timing of slip in each area. The total size of SMGAs is much smaller than the asperity area. This event coincides with empirical scaling relationships between total rupture area, asperity area, SMGA, and its seismic moment proposed for subduction-zone plate-boundary earthquakes by previous papers although the asperity abstracted for this event may have different nature from those of past smaller earthquakes.