A revised tsunami source model for the 1707 Hoei earthquake and simulation of tsunami inundation of Ryujin Lake, Kyushu, Japan

Based on many recent findings such as those for geodetic data from Japan's GEONET nationwide GPS network and geological investigations of a tsunami‐inundated Ryujin Lake in Kyushu, we present a revised source rupture model for the great 1707 Hoei earthquake that occurred in the Nankai Trough off southwestern Japan. The source rupture area of the new Hoei earthquake source model extends further, to the Hyuga‐nada, more than 70 km beyond the currently accepted location at the westernmost end of Shikoku. Numerical simulation of the tsunami using a new source rupture model for the Hoei earthquake explains the distribution of the very high tsunami observed along the Pacific coast from western Shikoku to Kyushu more consistently. A simulation of the tsunami runup into Ryujin Lake using the onshore tsunami estimated by the new model demonstrates a tsunami inundation process; inflow and outflow speeds affect transport and deposition of sand in the lake and around the channel connecting it to the sea. Tsunamis from the 684 Tenmu, 1361 Shokei, and 1707 Hoei earthquakes deposited sand in Ryujin Lake and around the channel connecting it to the sea, but lesser tsunamis from other earthquakes were unable to reach Ryujin Lake. This irregular behavior suggests that in addition to the regular Nankai Trough earthquake cycle of 100–150 years, there is a hyperearthquake cycle of 300–500 years. These greater earthquakes produce the largest tsunamis from western Shikoku to Kyushu.