Tsunami Hazard Along the Eastern African Coast from Mega-Earthquake Sources in the Indian Ocean

The catastrophic 2004 Indonesian tsunami reached the shores of Eastern Africa, where it affected at least 12 countries and caused several hundred casualties, principally in Somalia. Significant variations in run-up were documented by various post-tsunami surveys (note that the latter remain incomplete, especially in Southern Tanzania and Mozambique). In a previous study, Okal et al. (Okal et al. South Afr. J. Geol. 112:343–358, 2009) it has been suggested that these variations could depend on the precise location of the tsunami sources, as a result of the combined effect of source directivity and refraction by irregular bathymetry. In this context, we present the results of a significantly enhanced study, which considers a total of twelve potential sites of mega-earthquakes, along both the Sunda Arc, and the Makran subduction zone. Numerical simulations are carried out at a total of 25 virtual gauges, spanning the East African coast from Socotra in the north to Port Elizabeth in the south, as well as adjoining islands (Madagascar, Comoros, Mascarenes). In particular, we identify locations where the 2004 tsunami (which to a large extent awakened the awareness of the continent to tsunami danger) may not have represented the worst-case scenario.