SEDIMENTOLOGICAL RECORD OF TYPHOONS AND TSUNAMIS FROM SHIKOKU, SOUTHWESTERN JAPAN

The 2011 Tōhoku earthquake and consequent tsunami along with frequent typhoon strikes serve as stark reminders that natural hazards present a significant threat to the Pacific coast side of Japan. This region has a very long historic record of frequent typhoon strikes and devastating tsunamis, making Japan an ideal location to study and characterize sedimentological and geochemical signatures associated with typhoon and tsunami-derived deposits. Presently, instrumental records for natural hazards of these type extend only back to ~1945 AD. Geologic records retrieved from this region can be used to extend existing historic records even further, which, in turn, allows the risk associated with the frequency of these events in the region to be better established. Here we discuss records of typhoon and tsunami events recovered from terrestrial coastal ponds from three sites in Ehime Prefecture, southwestern Japan. A multi proxy approach consisting of loss on ignition, X-Ray fluorescence, density, X-radiograph, grain size, and magnetic susceptibility is used to characterize dense layers as marine-sourced material in sediment cores. Radiocarbon and short-lived isotopic analyses provide chronological age constraints. Characterized events consistently show spikes in strontium, magnetic susceptibility, and percent inorganic values. Events that correlate chronologically with this multi proxy approach across multiple sites are considered to be tsunami derived, whereas non-correlative events having localized event signals are likely associated with typhoons. This methodology is a powerful tool for distinguishing between typhoons and tsunamis, and for better assessing the return periods of natural disasters along the Pacific Japan coast.