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Magnitude 8.6 and 8.2 Earthquakes
April 11, 2012| Sumatra, Indonesia


On Wednesday, April 11 2012, two major and unusual earthquakes struck off the coast of Indonesia.  A magnitude 8.6 earthquake was reported around 2:40 pm local time followed by a magnitude 8.2 earthquake about 2 hours later.    Earthquakes of this size occur about once a year and are usually associated with vertical thrusting motions, initial reports on these earthquakes suggest that they had horizontal, strike-slip, motions.  The mainly horizontal strike-slip motion of both earthquakes renders the likelihood of a major tsunami to almost nothing, though an initial tsunami watch was generated by the 8.2 earthquake and there were reports of small less than 1 meter waves in some locations, no major tsunami or damage was reported.  Both earthquakes occurred far off the most active fault zones in the region and far from any major landmasses.  The 8.6 magnitude earthquake did generate moderate to strong shaking in the Banda Aceh region, but significantly less than a closer earthquake would have.

The size and location of these earthquakes had many people remembering the devastating magnitude 9.1 earthquake and tsunami that occurred in the region on Boxing Day December 2004 that killed more than 200,000 people in the Indian Ocean region.  However, despite their unusual size, these earthquakes were still significantly smaller than that earthquake and were a different type that doesn’t usually generate tsunamis. 

The earthquake waves from both earthquakes have been detected on the seismometers in South Carolina, though they would not be felt by anyone.

For more information contact:
Dr. Erin Beutel; Director of South Carolina Earthquake Education Center—College of Charleston
beutele@cofc.edu
cell: 843 478-5200

Image below generated using GEOMAPAPP—Dots are earthquakes within the last day, size and color indicate magnitude.

Dots are earthquakes within the last day, size and color indicate magnitude

Image below is historical seismicity in the region from 1990 to the present. Earthquake locations today marked by a star. Map is from the USGS website.

Historical seismicity in the region from 1990 to the present

Image of Indonesian earthquake waves picked up by South Carolina seismometers run by Tom Owens at University of South Carolina.

Image of Indonesian earthquake waves picked up by South Carolina seismometers run by Tom Owens at University of South Carolina




 
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Last Updated: April 11, 2012
Curator: hallcr@cofc.edu

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