Keywords:the 1605 Keicho Earthquake-Tsunami, Historical Earthquake, Historical Tsunami, Boso Peninsula, Japan Trench
The tsunami of the Keicho Earthquake of February 3, 1605 was recorded at the points on the Pacific coast of the western part of the Japanese Islands, and is sometimes regarded as one of the Tokai Gigantic earthquakes. In the present study we made clear the detailed distribution of heights of the tsunami of this earthquake on the open coast of the Boso Peninsula, Chiba Prefecture. The basic document of the present study is called “The Boso Chiran-ki” (Chronology of inner battle in Boso Peninsula), in which the names of 35 tsunami damaged villages were listed and the locations of these villages are shown by small circles in the Figure. There is a no damage coast of the lenghth of about 12 kilometers between Katsuura town and Uchiura village, which is presumable that only a slight damage took place in this coastal section. The Text of “Toudai-ki (The Chronology of the years under the rule of the first Shogun Ieyasu Tokugawa)” also recorded this tsunami, and seven villages in the territory of Ootaki clan were swept away and nothing left on the ground. The locations of these seven villages are shown by black diamonds in Figure. A temple called Saitokuji in Amatsura village in Kamogawa city, handed down an old document in which it is recorded that all houses were swept away in this village. We made a field measurement in those villages. We obtained the tsunami height distribution is shown as the figure. The tsunami height exceeded 10 meters at sixteen points. Considering this tsunami height distribution, the 1605 Keicho earthquake is not considered as one of the series of the Off-Tokai gigantic earthquakes.
Acknowledgement: This study was achieved as a part of the commissioned research named “Study on the historical tsunamis in the Pacific coast of Japan (2016)” on disaster prevention for nuclear facilities proposed by the Nuclear Regulation Authority, Japan.