Possible slip history scenarios for the Hyuga-nada region and Bungo Channel and their relationship with Nankai earthquakes in southwest Japan based on numerical simulations

The Nankai earthquakes are great interplate earthquakes with recurrence intervals of 100-200 years, occurring along the Nankai Trough, southwestern Japan. New geological evidences suggest that the rupture area of the 1707 earthquake (one of the largest) extended farther westward than previously thought, and similar magnitude events may have recurrence intervals of several hundred years. West of the Nankai earthquake segments, in the Bungo Channel region, slow slip events (SSEs) have occurred with recurrence intervals of several years since 1980. Farther westward, no M >= 7.5 interplate earthquakes have occurred except for one in 1968 in the northern Hyuga-nada region, near the Bungo Channel. We numerically simulated the generation cycles of Nankai earthquakes, Hyuga-nada earthquakes, and Bungo Channel SSEs to obtain possible slip histories in these regions, particularly during 1707-1980. We showed that the Nankai and Hyuga-nada earthquakes occur mostly independently, with average recurrence intervals of 151 and 117 years, respectively. An SSE patch slipped coseismically during both the Nankai and Hyuga-nada earthquakes. The rupture of the Nankai earthquakes extended to the Hyuga-nada region every similar to 500-600 years and was followed by quiescence of SSEs for more than 200 years. Subsequently, SSEs occurred repeatedly every 8 years. Current observational findings are generally consistent with the characteristics obtained from our scenarios, except regarding the recurrence intervals of Hyuga-nada earthquakes, for which few observations are available. Further evidence of the slip history in these regions will be required to use information from such simulations to forecast future earthquakes.