The Large Andaman Islands Earthquake of 26 June 1941: Why No Significant Tsunami?

Date: 4/26/2019

Time: 11:00 AM

Room: Pike

We present a modern seismological study of the earthquake of 26 June 1941 in the Andaman Islands, the largest pre-2004 event along that section of the India-Burma plate boundary. Despite a large conventional magnitude (#M sub PAS ^=^8.1#), it generated at best a mediocre tsunami for which no definitive quantitative reports are available. We show that the 1941 earthquake took place under the Andaman accretionary prism, and consisted of a composite event, whose nucleating phase had a strike-slip mechanism incompatible with a dataset of spectral amplitudes of mantle Rayleigh and Love waves. Combining this initial phase with a larger normal faulting mechanism can reconcile them with P-wave first motions, reports of subsidence on the Eastern coast of the Andaman Islands, and with the small amplitudes of any putative tsunami. The small tsunami results from a combination of that mechanism and of a source located under the islands themselves and in shallow water, implying a reduction in amplitude under Green's law when transitioning to a deeper basin.

Presenting Author: Emile A. Okal

Authors