TOTAL ANALYSIS OF THE 1993 HOKKAIDO-NANSEI-OKI EARTHQUAKE USING SEISMIC-WAVE, TSUNAMI, AND GEODETIC DATA

The fault geometry and slip distribution of the Hokkaido Nansei-oki, J apan, earthquake of July 12, 1993 are estimated using seismic wave, ts unami, and geodetic data. The Moment Tenser Rate Function inversion fr om P waves shows one nodal plane shallowly dipping to the west and the other nodal plane steeply dipping to the east. The best depth is esti mated as 10-15 km. The source time history consists of an initial puls e with a duration of 10 s and moment release of 2 x 10(20) Nm, followe d by a complex rupture for at least 40 s. The Centroid Moment Tenser ( CMT) solution shows one nodal plane shallowly dipping to the east and the other steeply dipping to the west. The overall seismic moment is e stimated as 5.5 x 10(20) Nm (M(W) 7.8). The joint inversion of geodeti c data on Okushiri Island and tsunami waveforms in Japan and Korea sho ws that the largest slip, about 6 m, occurred at a small area just sou th of the epicenter. This corresponds to the initial rupture on a faul t plane dipping shallowly to the west. The slip on the northernmost fa ult, dipping to the east, is about 2 m. The slips on the southern faul ts, dipping steeply to the west, are more than 3 m. Total seismic mome nt of 4.9 x 10(20) Nm, estimated from the slip distribution, is simila r to the estimate from CMT inversion.