Coastal Lake Hamana is positioned near the convergent tectonic boundary of the Nankai-Suruga Trough, along which the Philippine Sea slab subducts underneath the Eurasian Plate, giving rise to repeated tsunamigenic megathrust earthquakes (Mw≥8). A good understanding of the earthquake- and tsunami-triggering mechanisms in terms of rupture mode and recurrence pattern in time and space, is crucial in order to better estimate the complexity of seismic risks for the densely populated Enshu-nada coast. Based on existing historic data of paleoseismicity (last ~1300 years), the easternmost segment (Tokai) of the Nankai-Suruga Trough appears to exhibit a seismic gap and is expected to rupture in the near future, causing the next ‘Tokai earthquake’. Studying the sedimentary infill of Lake Hamana can help to fine-tune hazard assessment in the area of interest. Thanks to its extensive accommodation space, the Hamana lake basin is considered to be a good recorder of past events. Fieldwork (autumn 2014) comprised a reflection-seismic survey for imaging the lake’s stratigraphic features, based on which locations for gravity coring were selected. A systematic sampling of bottom sediments from different sites makes it possible to evaluate vertical as well as lateral changes in depositional environment, including event-deposits generated by earthquakes and tsunami. For identification of marine incursions caused by tsunami waves, a set of sedimentological, geophysical, geochemical and micropaleontological analyses are applied on the cored sequences. Radionuclide dating provides the necessary timeframe and information on prevailing sedimentation rates. Sites with the potential of recording complete and long event histories will be sampled with long cores during the upcoming field season (autumn 2015).
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