2015 年 25 巻 2 号 p. 61-67
Estimations of heights of past tsunamis are a key to forecast oncoming earthquakes and tsunamis. Generally, the heights of the historical tsunamis have been measured based on historical documents which describe actual marks of the tsunami inundation, such as “the tsunami came up to the fifth steps from the bottom in the temple”, and based on measurements of their heights by field surveys. However, some of the historical documents recorded only number of houses damaged due to the tsunamis. The records obviously indicate that the large tsunamis actually inundated. They are difficult to estimate the tsunami heights because they include no marks which the tsunami rose up to. Tsunami fragility can be useful to estimate the tsunami heights from the damage data, but no existing tsunami fragility targets historical tsunamis. Because strength of houses in historical era may be different from that in nowadays, formulation of tsunami fragility for historical tsunamis is necessary.