Research groups at the University of Tokyo, Tohoku University, and Osaka City University have conducted excavation of deposits along the southeastern coast of Sri Lanka, which was severely damaged by the Indian Ocean Tsunami caused by the 2004 Sumatra earthquake.More than eight tsunami events were identified from the approximately 8,000-year paleoenvironmental records of the sediment.
In the December 2004 Sumatra earthquake and tsunami, more than 12 people were killed or missing in more than nine countries along the Indian Ocean coast.Sri Lanka is located on the opposite bank of the epicenter of the Sumatra earthquake, and the country itself has few earthquakes, and it is unlikely that the coastline will rise due to earthquakes, so it is said that the southeastern coastal area accurately records tsunami records. NS.
The research group selected an excavation site based on the inundation information of the 2004 tsunami.A research raft was moored in the lagoon of Hambantota in southern Sri Lanka, and a core sample of 5 to 8 m was collected.We observed the details of the sediments and identified the sand layers that were thought to have been carried from the sea by the tsunami in the past.In addition, for detailed dating, fossils such as shellfish were collected and highly accurate radiocarbon dating was performed by an accelerator mass spectrometer.
As a result, it was clarified that the core sample obtained this time is a continuous geological record for the past 8,000 years, of which at least eight tsunami-induced strata have been recorded in the past 7,000 years.Regarding dating, it is extremely consistent with the research results of the American group that excavated in the same area, and by using sediment observation and shell fossil measurement together as in this case, it is possible to objectively identify the layer of the tsunami. There is a high possibility that it can be done.
This research is expected to be an important achievement in clarifying the actual conditions of past tsunamis and high-wave disasters and formulating future disaster mitigation plans in coastal areas.
