The Orphan Tsunami of 1524 on the Konkan Coast, Western India, and Its Implications

In comparison to the east coast, the tsunami hazard for the west coast of India remains under-recognized, despite the impact in 1945 following a M_w 8.1 earthquake in the Makran subduction zone in the northern Arabian Sea. The previous occurrences of tsunamis in the Arabian Sea that would have a bearing on the west coast of India are being debated, including the question whether the Makran region has the potential to generate greater-magnitude earthquakes. With this in the backdrop, we present here the historical and geological evidence of a tsunami impact zone from a site on the Konkan Coast of western India. Located in the village of Kelshi, the impact zone is preserved within a coastal dune complex that also reveals occupation layers. This laterally extending 30–40-cm-thick zone, coinciding with a habitation level, displays varied sedimentary structures including scour-fill features, and is inter-layered with shells, at a height of ~ 3 m from the high-tide level. We attribute these sedimentary features to a tsunami flooding event that was contemporaneous with the transportation of shells, dated at 1508–1681 CE. The geological inference matches with the description by the Portuguese fleets of a sea disturbance in 1524 CE, reported from Dabhol, not far from Kelshi, and also from the Gulf of Cambay, located about 500 km to the north. Precluding submarine landslide scenarios, the modeling results suggest that the high impact in Kelshi could have been generated by a M_w ≥ 9 earthquake sourced in the Makran subduction zone. It is, however, intriguing how a M_w ≥ 9 earthquake in the Makran region finds no mention in the historical documentation. We underscore the need for fresh efforts along the Makran coast to reconstruct the tsunami recurrence history that would generate required validating constraints on the 1524 event, if it was indeed generated by a massive earthquake among other mechanisms.