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

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 PAS = 8.1 ), it generated at best a mediocre tsunami for which no definitive q...

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Bibliographic Details
Published in:Pure and applied geophysics 2019-07, Vol.176 (7), p.2869-2886
Main Author: Okal, Emile A.
Format: Article
Language:English
Subjects:
Accretion
Amplitudes
Earth and Environmental Science
Earth Sciences
Earthquakes
Geophysics/Geodesy
Islands
Love waves
Plate boundaries
Seismic activity
Seismology
Shallow water
Tsunamis
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Summary: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 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 data set 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 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.
ISSN:0033-4553
1420-9136
DOI:10.1007/s00024-018-2082-8