Historical evidence warns about disastrous tele-tsunami risk on the coast of East Africa.

Abstract

The 2004 tsunami killed more than 200,000 people in Asia, but fewer than 300 in all East Africa. As a result, the search for ancient precursors has focused primarily along the coastlines of the Northern and Eastern Indian Ocean. No efforts to study past events were made in East Africa, leading to an underestimation of the tsunami risk in the region. Here we document a 1,000-yr old event that devastated a coastal Swahili settlement in Tanzania. Our study suggests a tsunami wave as the most likely explanation, in agreement with coeval tsunami deposits elsewhere across the Indian Ocean. Numerical simulations of tsunami flooding suggest a megathrust earthquake from the Andaman-Sumatra subduction zone as a potential source, with a larger magnitude than the 2004 event. Our findings indicate that tele-tsunamis represent a serious threat to coastal societies along the Western Indian Ocean, with implications for future tsunami hazard and risk assessments.