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In the initial hours following the origin of the Sumatra-Andaman Islands earthquake at 0058:53 GMT on 26 December 2004, the event was widely reported as having a magnitude of about 8. Thus, its potential for generating a damaging teletsunami (ocean-crossing tsunami) was considered minimal.

The event's size later was shown to be approximately 10 times larger, but only after more than four and a half hours had passed, when a moment estimate based on 2.5 hours of data became available from Harvard University's Centroid-Moment Tensor (CMT) Project (M.Netties and G. Ekstrom, Quick CMT of the 2004 Sumatra-Andaman Islands earthquake, Seismoware FID: BR345, e-mailed announcement, 26 December 2004). This estimate placed its magnitude at Mw ≈9.0, in the range capable of generating a damaging teletsunami. Actually, the earthquake had caused a teletsunami, one that by that time had already killed more than a hundred thousand people. The magnitude estimate has been subsequently revised to at least 9.3 (Stein and Okal, http://www.earth.northwestern.edu/people/∼seth/research/sumatra.html), with the exact magnitude of the event likely to be a subject of further research in the coming years.