Abstract:

The East and South China Seas are adjacent to the Ryukyu and Manila Trenches, where earthquakes occur frequently. Tsunami researches in the past were focused on analyzing historical documents and numerical simulation to assess the risk and history of tsunamis striking the coastline, but the knowledge of historical tsunami events was uncertain. In the past decade, by investigating coastal, marine sediments and their depositional processes, tsunami relics, and historical documents, we have developed research approaches to reconstruct paleotsunami. We first recognized a 1000-year-old tsunami based on sedimentary evidences from Dongdao and Xisha Islands and the South China Sea, and proposed using lake sediment characteristics as a criterion for identifying paleotsunami. Sampling and dating methods, including validation from both the age of the event layer and historical literature, were also proposed. We suggest that a tsunami occurred in the South China Sea in the past 1300 years, and the year of this event is AD 1076.To expand the age span of the reconstruction, a 2200-year-long sediment record from the East China Sea was studied. Disturbance caused by the South China Sea tsunami could be seen in the record, whereas the absence of a stronger abrupt change indicated the East China Sea has not been hit by catastrophic tsunamis in the past 2200 years. The 1076 tsunami hit the coastal regions of South China. Tsunami deposits containing shards of Song ceramics were preserved on the coast of Nan’ao Island; the culture of Nan’ao experienced a 500-year decline after the South China Sea tsunami and did not recover until the late Ming Dynasty. We used radiocarbon ages of plant remains and shell carbonates, OSL analysis of sand, and ceramic dating to determine the age of the paleotsunami; based on the dating results, we put forth the methods for tsunami deposit dating. In addition to these dating methods, proxies of geomorphology, geochemistry, and sedimentary sources can also be used under different depositional environments. The east coast of Hainan Island is also vulnerable to tsunamis, and future studies are needed to reconstruct its paleotsunami records.

Key words: paleotsunami, tsunami deposit, paleotsunami dating, the South China Sea, the East China Sea, coastal tsunami hazard