1997 年 49 巻 4 号 p. 461-466
A small tsunami accompanied with the Hyogoken-Nanbu earthquake on January 17, 1995 (epicenter: 34°36′N, 135°03′E, d=14km, M=7.2, JMA), was observed at many tidal stations around the source area. The maximum double amplitude at Ei, Awaji Island, reached 68cm, and those at most Stations were 10-20cm or less with the wave period of 10-20min. By judging from the diagram of the attenuation of wave-height with distance, tsunami magnitude on the Imamura-Iida scale was determined to be m=-2, which is smaller by two grades (amplitude: 1/5 less) than those generated by earthquakes of the same magnitudes, because the seismic faults lay on land. The size of the source area estimated by means of an inverse refraction diagram is 70×13km2 extending NE-SW direction from the Hanshin region to the western area of Awaji Island. The tsunami source comprehends the aftershock area. Considering the distribution of the initial motions of tsunami observed by tidegauges, it suggests that the sea-bottom on the east side of the northern tsunami source (the northern part of Osaka Bay) was uplifted and that on the west side (Harima-Nada Sea) was subsided.