In the wake of the 2011 Tohoku-oki tsunami, studies modelling rupture scenarios for the Japan Trench have identified areas of uncertainty, particularly along the southern segment. The accuracy of these seismic models and the understanding of fault movement along the southern Japan Trench can be greatly improved by locating and mapping prehistoric tsunamis deposits. Records of tsunamis developed from the sedimentary deposits they leave behind, improve our understanding by expanding the age range of events available for study. This EAGER research project, carried out by scientists from the University of Pennsylvania and the Geological Survey of Japan, aims to locate geologic evidence of past tsunamis originating from the southern segment of the Japan Trench, which to date remains undocumented. The study will investigate the beach ridges and coastal ponds of Chiba region of Japan using the state-of-the-art litho-, bio-, and chronostratigraphical techniques. The research is highly exploratory in nature since, as of yet, geologic evidence of paleo-tsunamis in this region has been found.
The importance of understanding the timing and magnitude of tsunamis originating from the Japan Trench was highlighted by the unexpected Mw 9.0 Tohoku-oki event in 2011. Despite generating the largest instrumental record of an earthquake, very little is known about the Japan Trench, particularly its southern segment near Tokyo. The establishment of a recurrence interval for tsunami generating earthquakes improve assessments of natural hazards to the Greater Tokyo Area, the largest metropolitan area in the world. This research will provide important new information concerning the uncertainty surrounding long-term earthquake patterns, not only for the Japan Trench, but also for other locations such as the Pacific coast of North America, Chile and Indonesia.
