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, Japan, earthquake of July 12, 1993 are estimated using seismic wave, tsunami, and geodetic data. The Moment Tenser Rate Function inversion from 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 estimated as 10-15 km. The source time history consists of an initial pulse with a duration of 10 s and moment release of 2 x 10(20) Nm, followed 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 estimated as 5.5 x 10(20) Nm (M(W) 7.8). The joint inversion of geodetic data on Okushiri Island and tsunami waveforms in Japan and Korea shows that the largest slip, about 6 m, occurred at a small area just south of the epicenter. This corresponds to the initial rupture on a fault plane dipping shallowly to the west. The slip on the northernmost fault, dipping to the east, is about 2 m. The slips on the southern faults, dipping steeply to the west, are more than 3 m. Total seismic moment of 4.9 x 10(20) Nm, estimated from the slip distribution, is similar to the estimate from CMT inversion.