Detailed coseismic slip distribution of the 1944 Tonankai earthquake estimated from tsunami waveforms

Coseismic slip distribution on the fault plane of the 1944 Tonankai earthquake is estimated from inversion of tsunami waveforms. Three improvements from a previous study [Satake, 1993] are made. These are: (1) smaller subfaults are used to resolve detailed slip distribution; (2) the subfaults fit better to the plate interface geometry; and (3) finer and more accurate bathymetry data is used. The inversion result shows that a maximum slip of about 3 m occurred on the plate interface off Shima peninsula. The total seismic moment is estimated to be 2.0 X 10(21) Nm (M-W 8.2). The result confirms that the 1944 Tonankai earthquake did not rupture the plate interface beneath the Tokai region and supports the existence of the seismic gap in the Tokai region suggested by Ishibashi [1981]. The slip of about 1.5 m on the plate interface beneath Atsumi peninsula, northeast of the large slip area, is necessary to explain the observed tsunami waveforms, although no seismic moment release was estimated from strong motion data by Kikuchi ct al. [1999]. This may suggest that the rupture beneath Atsumi peninsula was slow.