Coral boulders along the coast of the Lanyu Island, offshore southeastern Taiwan, as potential paleotsunami records

Abstract In the last decade, several disastrous tsunamis hit a large area of coastal East Asia, and produced numerous casualties and economic losses. As a country that is also prone to tsunami hazards, Taiwan is in urgent need for more knowledge of past tsunami records and potential tsunamigenic sources. On the basis of detailed geomorphic mapping and field investigations, we identified six sites in the northern part of the Lanyu Island, offshore southeastern Taiwan, with large coral boulders resting on Holocene uplifted coral reef terraces. Boulders of these six sites are all likely moved by extremely strong waves, and four sites have better constraints to suggest that the boulders may indeed be transported during a paleotsunami event. The ages of the boulders suggest that the extremely strong wave events occurred at least several times since the mid-Holocene high stand of sea level. The youngest event may correlate with the 1771 Meiwa tsunami of the southern Ryukyu Islands, but it is more likely to be produced by some undocumented event along the eastern coast of Taiwan. The locations of the coral boulder sites along the northern coast of the Lanyu Island suggest that the sources of the events are located to the north of the island. We believe that our results would provide further information for future tsunami hazard assessments along the eastern coastal area of Taiwan, as well as surrounding areas.