The great Kurile Earthquake of October 4, 1994 tore the slab

The fault geometry, depth, and slip distribution of the Kurile earthquake of Oct. 4, 1994 are estimated using seismic waveforms, aftershock distribution, geodetic measurements, and tsunami waveforms. Previous large earthquakes in the Kurile arc had typical underthrusting focal mechanisms due to the local subduction. Seismic wave inversions of the 1994 event indicate a thrust type mechanism with a large strike-slip component. This does not represent an underthrust event at the subduction interface. The focal depth is estimated at 50 kin, just beneath the previously estimated subduction interface. We calculate crustal deformation and tsunami waveforms from the two possible fault planes of the focal mechanism solution and find that both fault planes explain the observations. We choose the north-south striking plane, because of the occurrence of a large (M w 7.8) intermediate-depth earthquake on Dec. 6, 1978, northwest of the 1994 rupture area. The lineation of aftershock distributions of these two events suggests that both earthquakes were due to a tearing of the slab perpendicular to the trench. The joint inversion of geodetic and tsunami data shows that the largest slip, about 17 m, occurred at the upper end of the slab.