Abstract
Two strong earthquakes occurred off the southeastern coast of Hokkaido in northern Japan on 26 September 2003. The earthquakes gave various damage in the southeastern part of Hokkaido. A number of tsunamis associated with the earthquakes have been observed on the southern coast of Hokkaido as well as the northern part of Japanese mainland. The characteristics of the tsunami are that the wave propagation exceptionally continued longer than a day because of the generation of edge wave, and the tsunami ascended many rivers as much as approximately 10km away from the river mouth. In this paper, the properties of the river-runup of the tsunami were discussed on the basis of the hydrographs of the water level and results of the field surveys on Tokachi river, Kusiro river, Saru river and Mu river. We pointed out that understanding the risk of the river-ascending tsunami is particularly important for hazard mitigation.
