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Official Report

The following report is extracted from USGS Earthquake Information Centre.

Preliminary Earthquake Report
U.S. Geological Survey, National Earthquake Information Center
World Data Center for Seismology, Denver

The devastating megathrust earthquake of December 26, 2004, occurred on the interface of the India and Burma plates and was caused by the release of stresses that develop as the India plate subducts beneath the overriding Burma plate.

The India plate begins its descent into the mantle at the Sunda trench, which lies to the west of the earthquake's epicenter. The trench is the surface expression of the plate interface between the Australia and India plates, situated to the southwest of the trench, and the Burma and Sunda plates, situated to the northeast.

At region of the earthquake, the India plate moves northeast at a rate of about 6 cm/year relative to the Burma plate. This results in oblique convergence at the Sunda trench. This motion is partitioned into thrust-faulting, which occurs on the plate-interface and involves slip directed perpendicular to the trench, and strike-slip faulting, which occurs several hundred kilometers to the east of the trench and involves slip directed parallel to the trench.

The December 26 earthquake occurred as the result of thrust-faulting.

Preliminary locations of larger aftershocks following the megathrust earthquake show that approximately 1200 km of the plate boundary slipped as a result of the earthquake. From the size of the earthquake, it is likely that the average displacement on the fault plane was about 15 meters. The sea floor overlying the thrust fault would have been uplifted by several meters as a result of the earthquake.


  • USGS Earthquake Hazards Program-Latest Earthquakes. US Geological Survey. Retrieved March 5, 2005, from http://earthquake.usgs.gov/eqinthenews/2004/usslav/
  • 26 December 2004 Tsunam. National Institute of Oceanography, India. Retrieved March 5, 2005, from http://www.nio.org/jsp/tsunami.jsp
  • Tsunami!: The WWW Tsunami Information Resource. Earth and Space Sciences (Geology and Geophysics) at UW. Retrieved March 5, 2005, from http://www.ess.washington.edu/tsunami/toc.html
  • Sumatra Earthquake 26 December 2004. British Geological Survey. Retrieved from http://www.earthquakes.bgs.ac.uk/latest_info.htm

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