Western Sumatra: Major Seismological Hotspot
The complexity of the tectonic situation in the western Indian Ocean means that the area is notable both for its earthquakes and its volcanoes (the major historic eruptions of Krakatoa, Tambora and, in prehistoric times, Toba are all products of this subduction zone). Earthquakes of M7 or greater are by no means uncommon, as maps of historical seismicity show: there have been 24 tremors of this size in the past decade.
In the past decade, however, the subduction of crust below Sumatra has generated three extremely large tectonic events. To the north of the island (where the January 2012 earthquake occurred) the waters have been the source of the devastating Magnitude 9.1 Boxing Day earthquake of 2004 (which killed over a quarter of a million people) and the only slightly smaller M8.6 event of March 2005, while further south the same subduction zone saw the M8.5 event of September 2007.
California Institute of Technology Tectonics Observatory. Why Earthquakes and Tsunamis occur in the Sumatra Region. Accessed January 11, 2012.
Reuters. Indonesia lifts tsunami warning after Sumatra quake. Accessed January 11, 2012.
USGS Earthquake Hazards Program. Magnitude 7.3 – off the west coast of northern Sumatra. Accessed January 11, 2012.
USGS Indonesia. Seismotectonics of the Indonesian Region. Accessed January 11, 2012.
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