The slip distribution of the 1946 Nankai earthquake estimated from tsunami inversion using a new plate model

A new model for the shape of the Philippine Sea Plate (PSP) subducting beneath southwest Japan was constructed by combining marine seismic survey results and seismicity data. This resulted in a plate model that is generally 3–5 km shallower than previous estimates, and contains new details of plate boundary structure near the Nankai Trough axis. We estimated the slip distribution of the 1946 Nankai earthquake by inverting tsunami waveforms using the new plate boundary model, and found that the large slip off Cape Muroto and seismic moment were reduced by about 10% from the previous estimate of Tanioka and Satake (2001a). However, we also found reason to suspect the tide gauge closest to the epicenter (at Shimotsu), and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area. We also find that our new rupture model correlates well with features of the subducting plate boundary, such as a large subducting seamount off Cape Muroto (Kodaira et al., 2000a). This suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy, or both.