Geohazards in coastal areas near the northernmost Sagami Trough, central Japan: review of neotectonic activity in onshore and offshore areas of the Izu island arc collision–subduction zone

Abstract

AbstractThe northernmost coast of Sagami Bay, central Japan, is situated in the eastern part of the Izu island arc collision–subduction zone where the Philippine Sea Plate has been subducted beneath the Eurasian Plate or North American Plate since the middle Miocene. It is an area at high risk of geological disaster because it is a developed suburban area located just 50–80 km SW of the megalopolis of Tokyo. We have used our own onshore and offshore neotectonic field data to create a summary of the geological and topographical information related to geohazards over various spatial and temporal ranges, and we provide additional information from archaeological and historical disaster records. The geological hazards and disasters are reviewed on a logarithmic timescale from 10 Ma to modern times. We examine this information with respect to the Great Kanto earthquakes that have repeatedly affected the present area, as they provide a typical example of hazard history on a collision–subduction zone that is useful not only for assessing the local risk but also for providing generic risk. The results can assist in preparedness for various geological hazards, particularly earthquakes, tsunamis, and crustal movements such as uplift and subsidence, as well as active faults and folds.