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Location of earthquake on a global map
Tectonics of Sumatra-Andaman Islands
Tsunami wave field in the Bay of Bengal. View to the north west, focused near the earthquake epicenter (northern Sumatra).
(see a larger version of this image, 117 kb)
The December 26, 2004 M=9.0 Sumatra earthquake occurred along a subduction zone in which the India Plate, an oceanic plate, is being subducted beneath the Burma Plate. Below is a general diagram of an oceanic subduction zone.
Oceanic Subduction Zone
(Figure is taken from online edition of This Dynamic Earth)
The interface between the two plates results in a large fault, termed an interplate thrust or megathrust, that can traced along an arc parallel to the Sunda Trench from Myanmar to Java. The figure below, from the USGS Earthquake Hazards Program Earthquake Summary Poster, shows:
- the interplate thrust,
- the epicenter of the December 26, 2004 mainshock, and
- major strike slip faults in the overriding plate of the subduction zone.
Tectonic base map of the Sumatra subduction zone showing major faults. Map taken from USGS Earthquake Summary Poster
(see a larger version of this image, 162 kb)
See also: USGS National Earthquake Information Center (NEIC) Preliminary Earthquake Report
The direction of convergence of the India Plate relative to the overriding plate of the subduction zone (thick arrows on map above) is oriented oblique to the trench axis. For an oblique subduction zone such as this, strain can be partitioned one of two ways as shown in the figure below (from Geist, 1999; see also Michael, 1990).
As described in a classic paper by Fitch (1972), the Sumatra subduction zone is characterized by decoupled faulting, as in (b) above. In this case, nearly pure thrust faulting occurs along the interplate thrust and transcurrent, strike-slip faulting occurs in the overriding plate, most notably along the Great Sumatran fault. For contrast, the northern Puerto Rico subduction zone appears to be an example of oblique faulting, as in (a) above.
Please refer to Moore et al. (1980), Newcomb and McCann (1987), Krishna and Sanu (2002) and Milsom who discuss the seismotectonic environment of the Sumatra subduction zone in detail.
Seismological Aspects of Tsunami Generation (70 kb)
Contents:
Tectonics of Sumatra-Andaman Islands (81 kb)
Seismological Aspects of Tsunami Generation (70 kb)
Tsunami Generation Modeling (58 kb)
References
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