Large Holocene tsunamis in the northern Arabian Sea

Tsunamis have repeatedly hit the shores of Oman (Northern Arabian Sea) in historical times (e.g. 1945, 2013). These events had small (< 3 m) wave heights and short inundation distances, but it is unclear if much stronger events can affect the area. Boulder deposits and fine-grained sediments are described from the north coast of Oman, which are interpreted as evidence for much larger pre-historic tsunami events. No systematic dating was available, which hampers interpretation. In this paper we report radiocarbon dating results for marine organisms in these deposits and present luminescence dating of fine-grained units. We document new sedimentological and archaeological evidence for past tsunamis and describe new data on the impact of the 1945 Makran tsunami in Oman. Since the coast of Oman is prone to tropical storms, we discuss the possibility of sediment transport by cyclones and we compare our findings with recent evidence of boulder transport by storms worldwide. We argue that our results favor an interpretation as tsunamites based on sedimentological, archaeological, and spatial criteria. The dating results allow us to show that a tsunami hit the northern coast of Oman around 1000 years ago. A comparison with historical tsunami impact indicates that this palaeo-event exceeded in size all modern examples in the study area. We speculate that only a large earthquake at the Makran Subduction Zone can produce a tsunami of this size. In that case, the earthquake might have at least partially ruptured the western Makran, which would imply that the western Makran is not completely unlocked. Hazard scenarios based on historical data underestimate the tsunami threat in the Northern Arabian Sea.