Poster of the Andaman Islands, India Earthquake of 10 August 2009 - Magnitude 7.5

Tectonic Summary

The Andaman Islands earthquake of August 10, 2009, occurred in the boundary region of India plate and the Burma plate, near the north end of the rupture zone associated with the great Sumatra-Andaman earthquake of December 26, 2004. Early analysis of seismographic data implies that the earthquake occurred as the result of normal faulting on a north-northeast or northeast trending fault plane. This style of faulting is consistent with the earthquake occurring as a result of stresses generated by bending of the India plate as it subducts beneath the Burma plate. The August 10 earthquake was therefore an intraplate earthquake, in contrast to the great 2004 earthquake, which was an interplate thrust-fault earthquake on the interface between the India plate and the Burma plate.

Although the style of faulting that caused the August 10, 2009 earthquake differs from the style of faulting that caused the great 2004 earthquake, it is possible that changes in regional tectonic strain-field caused by the 2004 earthquake made conditions more favorable for the occurrence of the 2009 earthquake than would otherwise have been the case. It is noteworthy that in the days immediately following the 2004 earthquake there were a large number of normal-faulting earthquakes in the subducted India plate of the Andaman Islands region. The largest Andaman Islands intraplate normal-fault earthquake in the immediate aftermath of the 2004 earthquake was more than an order of magnitude smaller than the August 10, 2009, earthquake.