Geological Records of a 1000-Yr-Old Extreme Tsunami Event Revealed by Drill Cores in Qiongzhou Strait

Abstract

In AD 1076, a super tsunami hit the South China Sea islands and the coasts of Guangdong and Vietnam. However, the impact on Hainan Island, situated farther from the tsunami source, remains unclear. Tsunami modeling indicates that seismic tsunamis from megathrust earthquakes in the Manila Subduction Zone may affect Guangdong, Hainan and Vietnam. This study found tsunami deposits in core HZK14 from southeastern Qiongzhou Strait, Hainan, characterized by increased grain-size anomalies, coexistence of young and old ages, and mixed microfossils from nearshore and middle-shelf settings. The youngest shell 14C age from the core is AD 1100, which is close to the age of the AD 1076 tsunami event. Combined with geological records and historical documents, we conclude that tsunamis from the Manila Subduction Zone can reach Hainan’s coast. This has significant implications for tsunami risk assessment and for the development of the Hainan Free Trade Zone. It also provides valuable constraints for tsunami simulations in the South China Sea.