A Combined Earthquake–Landslide Source Model for the Tsunami from the 27 November 1945Mw 8.1 Makran Earthquake

Abstract

The tsunami of 27 November 1945 from an M w 8.1 earthquake in the Makran subduction zone is the only instrumentally recorded and deadly tsunami in the northwest Indian Ocean; offshore Iran, Pakistan, Oman, and India. Despite the fact that some source models have been proposed based on seismic or far‐field tsunami data, none of them was able to reproduce one important observation: near‐field runup of 10–12 m. Here, we applied numerical modeling and examined three possible secondary sources: (1) splay faulting, (2) delayed rupture of the earthquake source, and (3) submarine landslides. These secondary sources were added to the existing state‐of‐the‐art earthquake source for this tsunami. Results of simulations revealed that only a submarine landslide with dimensions of 15 km (length) × 15 km (width), a thickness of 600 m, a volume of ∼40 km3, and located at 63.0° E, 24.8° N is capable of reproducing the near‐field tsunami observation. Such a combined earthquake–landslide source is consistent with all available observations including far‐field tsunami waveforms in Karachi (Pakistan) and Mumbai (India), with near‐field runup height of 10–12 m, coastal coseismic deformation data in Pasni (subsidence) and Ormara (uplift ∼1–3 m), and earthquake magnitude ( M 8.0–8.3). [Electronic Supplement:][1] Tables listing parameters of the splay fault and landslide scenarios, and figures showing deformation and coastal tsunami amplitudes from splay fault and landslide scenarios. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160196/-/DC1