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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L08305, doi:10.1029/2004GL022320, 2005

Contiguous rupture areas of two Nankai Trough earthquakes revealed by high-resolution tsunami waveform inversion

Toshitaka Baba

Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan


Phil R. Cummins

Minerals and Geohazards Division, Geoscience Australia, Canberra, A. C. T., Australia


Abstract

We have developed a new method for inverting tsunami waveforms that reveals considerable detail in megathrust slip during subduction zone earthquakes. Previous methods have ensured compliance with the shallow-water theory used to compute tsunami waveforms by using large subfaults that generate only long-wavelength seafloor deformation. We show that a better approach is to use small subfaults coupled with a smoothing criterion that ensures compliance with the shallow-water approximation. In an application of the method to historical earthquakes in the Nankai Trough, southwestern Japan, we find that the areas with slip > 1 m for the earthquakes of 1944 and 1946, which ruptured adjacent segments of the subduction zone, are separated by a sharp, non-overlapping boundary. This establishes that interseismic accumulation of strain energy extends very close to the boundary between rupture zones, and strongly suggests that this boundary is associated with a physical barrier to rupture.

Received 27 December 2004; accepted 22 March 2005; published 19 April 2005.

Index Terms: 4564 Oceanography: Physical: Tsunamis and storm surges; 7209 Seismology: Earthquake dynamics (1242); 7240 Seismology: Subduction zones (1207, 1219, 1240).

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Citation: Baba, T., and P. R. Cummins (2005), Contiguous rupture areas of two Nankai Trough earthquakes revealed by high-resolution tsunami waveform inversion, Geophys. Res. Lett., 32, L08305, doi:10.1029/2004GL022320.