Tsunami records of the last 8000 years in the Andaman Island, India, from mega and large earthquakes: Insights on recurrence interval

As many as seven tsunamis from the past 8000 years are evidenced by sand sheets that rest on buried wetland soils at Badabalu, southern Andaman Island, along northern part of the fault rupture of the giant 2004 Aceh-Andaman earthquake. The uppermost of these deposits represents the 2004 tsunami. Underlying deposits likely correspond to historical tsunamis of 1881, 1762, and 1679 CE, and provide evidence for prehistoric tsunamis in 1300–1400 CE, in 2000–3000 and 3020–1780 BCE, and before 5600–5300 BCE. The sequence includes an unexplained hiatus of two or three millennia ending around 1400 CE, which could be attributed to accelerated erosion due to Relative Sea-Level (RSL) fall at ~3500 BP. A tsunami in 1300–1400, comparable to the one in 2004, was previously identified geologically on other Indian Ocean shores. The tsunamis assigned to 1679, 1762, and 1881, by contrast, were more nearly confined to the northeast Indian Ocean. Sources have not been determined for the three earliest of the inferred tsunamis. We suggest a recurrence of 420–750 years for mega-earthquakes having different source, and a shorter interval of 80–120 years for large magnitude earthquakes.