In the wake of the devastating 2011 Tōhoku earthquake and tsunami, the Central Disaster Management Council of the Japanese Cabinet Office issued new guidance for assessing seismic hazards in Japan. Before 2011, seismic hazard assessment relied on source models developed from knowledge of a small number of well-documented historical earthquakes. Less well-known historical earthquakes, including the AD 869 Jōgan Sanriku earthquake, were largely disregarded as their seismic intensities or tsunami heights could not be reconciled with the chosen seismic sources. Following the unexpectedly large size of the Tōhoku earthquake, the Cabinet Office advocated renewed investigation of earthquake and tsunami occurrence over historical and longer timescales, with a particular focus on defining the largest possible magnitudes. The new guidelines pay close attention to the Nankai Trough, the subduction zone where the Philippine Sea Plate dives beneath the Eurasian Plate. The Nankai Trough faces the densely populated and highly industrialised coastline of south central Japan and harbours a widely-known seismic gap along its eastern Tōkai segment. A full-length rupture of the Nankai Trough, including the Tōkai segment, could produce an earthquake with a magnitude approaching that of the 2011 event, with tsunami travel times to the closest shorelines of less than 30 minutes. Here, we review geological evidence for past earthquakes and tsunamis along the Nankai Trough. This evidence comes from a wide variety of sources, including uplifted marine terraces, turbidites, liquefaction features, subsided marshes and tsunami deposits in coastal lakes and lowlands. Examining papers published before and after 2011, we investigate the impact of the new Cabinet Office guidelines on attempts to understand the magnitude and recurrence of these events. We summarise current knowledge of the largest paleoearthquakes and paleotsunamis and make recommendations for further investigations of this highly critical subduction zone.

Abstract of an Oral Presentation or a Poster