Abstract
Adding the newly data of the 1994 Sanriku-Oki tsunamis, the distribution of the radiating tsunami energy off Sanriku, North Japan, is investigated during the last 100 years, 1896-1995. Judging from the diagram of the attenuation of wave-height with distance, magnitudes of the Sanriku-Oki tsunamis on Apr. 8, and Dec. 28, 1994 are m=-1 and m=1.5 on the Imamura-Iida scale, respectively. These values are normal compared to earthquake magnitudes (M=6.6 and M=7.5). The source area of the tsunami on Dec. 28, 1994 corresponding to an aftershock area lays extending about 150km to the unusual E-W direction. During 1896-1959, the maximum cumulative energy was radiated in the source area of the 1896 Sanriku tsunami (m=3.5) with the order of 1020 ergs per 15′ mesh. And the areas of radiated energy of 1018 ergs extend to Shimokita Peninsula and the Miyagi coasts. On the contrary, the amount of cumulative energy during 1960-1995 drops 1019 ergs and the radiated area moves to the north side. The remarkable seismic gaps still remain near Shimokita Peninsula and the trench side far off Miyagi Prefecture.
