The 1945 Makran tsunami in Karachi Harbour

Brian Atwater, USGS Seattle / University of Washington

Wednesday, July 12, 2017 at 10:30 AM

Location:
Building 3, Rambo Auditorium
Host:
John Tinsley

Effects of a 1945 tsunami in Karachi Harbour highlight risk from the Makran Subduction Zone. The most damaging of the tsunami waves arrived four hours after an earthquake of M 8.0–8.2 from a thrust source some 300 km to the west. The waves registered at a tide gauge and in local newspapers, government documents, and memories. Tide-gauged anomalies may include a precursory drawdown beginning an hour before the canonical earthquake. Exposure to tsunamis has grown since 1945 through a tenfold rise in fishing-village population and a twentyfold increase in import-and-export tonnage. A draft folio on the 1945 tsunami, prepared with United Nations and State Department support, aims to boost awareness of this growing risk.
These efforts scarcely make a dent in unknowns about Makran subduction hazards. As currently understood, the subduction thrust may or may not break in the west, beside Iran and Oman, as well as in the east, where the 1945 rupture extended an estimated 100–150 km along what is now Pakistan. M 9 ruptures 800 km long have been posited without recognized geological precedents. Abyssal turbidites ascribed to Makran earthquakes have not been calibrated to 1945. Security issues limit coastal field work in Pakistan. Coastal boulders reported from Oman and Iran may be explained by storm waves. The largest waves of the 1945 tsunami, in recent computer simulations, are set off by submarine slides.

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