台湾・フィリピン・インドネシアにおける津波規模の特性
1994 年 47 巻 2 号 p. 155-162
詳細
1994 年 47 巻 2 号 p. 155-162
Many tsunamis which were generated in the SE. Asia region hit the neighboring coasts of the source areas and some tsunamis were observed at the tidal stations of Japan. Tsunami magnitudes on the Imamura-Iida scale are investigated by the author's method 1 (HATORI, 1979, 1986) using the data of inundation heights near the source areas and the tide-gauge records in Japan. The regional characteristics of tsunami magnitudes are discussed in relation to earthquake magnitudes during the period from 1960 to 1993.
Comparing with the statistical relation of earthquake magnitudes based on the data near Japan and great earthquakes in the world, the magnitude values of the Taiwan tsunarmi sunamis showed relatively to be small. On the contrary, the magnitudes of tsunamis in the vicinities of Philippine and Indonesia exceed more than 1-2 grade (tsunami heights: 2-5 times) compared with the same earthquake magnitude of other regions. The relation between tsunami magnitude, m, and earthquake magnitude, Ms, is expressed as m=2.66Ms-17.5 for these regions. For example, the magnitudes for the 1976 W. Mindanao tsunami (Ms=7.8, 3702 deaths) and the 1992 N. Flores Is. tsunami (Ms=7.5, 1713 deaths) were determined to be m=3 and m=2.5, respectively.
The focal depth of tsunamigenic earthquakes is shallower than d<36km, and the detectivity of tsunamis is small for deep earthquakes being d>40km. For future tsunamis, it is indispensable to take precautions against shallow earthquakes having the magnitudes Ms<7.0.
