1999 年 52 巻 3 号 p. 369-377
A method for determining the tsunami magnitude Mt from tsunami run-up heights is developed by using the Abe's (1989) relation which has been employed for estimating run-up heights from earthquake magnitudes. The magnitude Mt is estimated from the relation, Mt=2logHm+6.6, where Hm is the maximum value of the local-mean run-up height in meters and the logarithmic mean of heights is taken over a distance of about 40km along a coast. Except for unusual events, the moment magnitude can be estimated from Mw=Mt-2C, where C=0 for tsunamis in the fore arc and C=0.2 for tsunamis in the back arc. For 12 large tsunamis that occurred around Japan from 1894 to 1998, Mw estimated from Mt is found to be essentially equivalent to that estimated from seismic waves. The present method is applied to determining Mt for 21 historical tsunamis that occurred around Japan on and after the 15th century. There are 13 large tsunamis with Mt=8 or over for the period from 1498 to 1893.