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ArticleA 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa: reply(Geological Society of America, 2020-12-22) Maselli, Vittorio ; Oppo, Davide ; Moore, Andrew L. ; Gusman, Aditya Riadi ; Mtelela, Cassy ; Iacopini, David ; Taviani, Marco ; Mjema, Elinaza ; Mulaya, Ernest ; Che, Melody ; Tomioka, Ai Lena ; Mshiu, Elisante ; Ortiz, Joseph D.We appreciate Somerville’s (2020) interest in our work, and the opportunity to further expand the discussion about the occurrence of a trans-oceanic tsunami in the Indian Ocean generated by a megathrust earthquake ~1000 years ago. Somerville suggests a connection between the inferred tsunami deposit presented by us (Maselli et al., 2020) and a tsunami event reported to have occurred in Nagapattinam (India) in the year 900 CE and described in Kalaki Krishnamurty’s book (Rastogi and Jaiswal, 2006).
ArticleA 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa(Geological Society of America, 2020-05-12) Maselli, Vittorio ; Oppo, Davide ; Moore, Andrew L. ; Gusman, Aditya Riadi ; Mtelela, Cassy ; Iacopini, David ; Taviani, Marco ; Mjema, Elinaza ; Mulaya, Ernest ; Che, Melody ; Tomioka, Ai Lena ; Mshiu, Elisante ; Ortiz, Joseph D.The December 2004 Sumatra-Andaman tsunami prompted an unprecedented research effort to find ancient precursors and quantify the recurrence time of such a deadly natural disaster. This effort, however, has focused primarily along the northern and eastern Indian Ocean coastlines, in proximal areas hardest hit by the tsunami. No studies have been made to quantify the recurrence of tsunamis along the coastlines of the western Indian Ocean, leading to an underestimation of the tsunami risk in East Africa. Here, we document a 1000-yr-old sand layer hosting archaeological remains of an ancient coastal Swahili settlement in Tanzania. The sedimentary facies, grain-size distribution, and faunal assemblages indicate a tsunami wave as the most likely cause for the deposition of this sand layer. The tsunami in Tanzania is coeval with analogous deposits discovered at eastern Indian Ocean coastal sites. Numerical simulations of tsunami wave propagation indicate a megathrust earthquake generated by a large rupture of the Sumatra-Andaman subduction zone as the likely tsunami source. Our findings provide evidence that teletsunamis represent a serious threat to coastal societies along the western Indian Ocean, with implications for future tsunami hazard and risk assessments in East Africa.