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Large Earthquake Pair: September 29-30, 2009

Samoa magnitude 8.0 Earthquake and Sumatra 7.6 earthquake

  • AUTHOR: Debi Kilb
  • DATE: 2009-09-30


A magnitude 7.6 earthquake occurred in southern Sumatra, Indonesia (99.961°E, 0.789°S, 80 km deep) on 30 September 2009 at 10:16:09 UTC. This earthquake occurred ~350 km north of the Mw 8.4 September 2007 earthquake and ~300 km south of the 8.7 earthquake of March 2005. The last large earthquake in this region was an earthquake of magnitude 8.5 or larger in 1797 (magnitude not constrained because of lack of recording abilities at that time). One day prior to the 30 September 2009 earthquake there was a magnitude 8 earthquake near the Samoan Islands (172.073W, 15.558S, 18 km deep). A causal relationship between these two earthquakes can not be ruled out, but because both of these regions are seismically active and are known to produce large earthquakes, in combination with the large distance between the two earthquakes (~1000 km), it is difficult to confirm if the first earthquake triggered the second earthquake. This interactive 3-D visualization includes the location of both of the mainshock epicenters (red diamonds), mainshock hypocenters (red stars), historical seismicity (~77,000 pink points), EarthScope’s USArray seismic station locations (orange cylinders), IDA seismic network stations (yellow cylinders) an outline of the USA (yellow lines), and topography/bathymetry of the region.


Links to websites:
http://anf.ucsd.edu/spevents/2009/273/a/
http://anf.ucsd.edu/spevents/2009/272/a/
http://anf.ucsd.edu/spevents/2009/272/a/samoa1.jpg
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