The Sedimentological Record of Upper Holocene Tsunami Event in Fengbin, Taiwan

Abstract

A tsunami had struck the Ami tribe’s settlement on the eastern coast of Taiwan in 1771. The trigger of this tsunami is still debatable. Hence, the analysis of tsunami deposits in Fengbin is needed to understand the chronology of the tsunami. There are three types of sediment samples taken from the study area, namely modern beach sand, modern fluvial sand, and sediment materials from the marine terrace. Sample analysis was carried out using the point counting, granulometry, biozonation, and paleo-bathymetry methods to determine the facies, provenance, and sediment transport mechanisms. The results of field observation indicate the presence of marine shells on the sediment deposit of marine terraces at elevations between 10.5-12.5 m. The thickness of this deposit is between 15-20 cm in the fining upward succession and there is a rip-up clast sedimentary structure. The characteristic of this deposit is similar to tsunami deposits found on the Ishigaki and Miyako Islands, Japan. The conclusion of this study is that there is a tsunami deposit in Fengbin associated with the tsunami deposits found in Miyako and Ishigaki Islands, Japan. The trigger of the tsunami in Fengbin probably attributed to tectonic activity in the Ryukyu Trench.