Abstract
A large tsunamigenic earthquake occurred off Adak Island at 4h 03m (UT), June 10, 1996. According to USGS, the epicenter is 51.564°N, 177.632°W with earthquake magnitude MS=7.6. Four hour later, small tsunami (double amplitude: 10-25cm, wave period: about 20min) was observed at the Japanese tide stations. By use of the diagram of the attenuation of wave-height with distance, tsunami magnitude on the Imamura-Iida scale is estimated to be m=2.0, which the value is similar to that of the 1986 Aleutian tsunami. The observed amplitudes in Japan for the past six Aleutian tsunamis were about 1/4 times smaller than those at the Hawaiian Islands. The directivity of tsunamis toward Japan is small, but in case of the source areas locating the East longitude region becomes effective. The average velocities of the maximum wave arriving in the Japanese Islands are scattered in the range of 240km/h to 470km/h. The velocity of large tsunamis (1946, 1957 and 1965) is rather slow, suggesting the propagation of edge waves along the continental slope.
