A LATER PHASE DETECTED BY TRIPARTITE OBSERVATION AT SUMIYOSHI, KOBE

A later phase propagating horizontally southeast was detected to the s outh of Japan Railway line in the lowlands of Sumiyoshi, Kobe, by the tripartite installed at the Nada junior high and high school station o f the Sumiyoshi Linear Seismic Observation Array, for aftershocks of t he 1995 Hyogo-ken Nanbu earthquake. A frequency wave-number spectral a nalysis revealed a phase velocity of 300-400 mis and energy concentrat ion in the frequency range 2.0-4.0 Hz. According to the delay after S- wave arrival, its phase velocity and its propagating direction, it is believed this phase was a secondary wave converted from incident S-wav e al the geological fault along the base of the Rokko mountain range.