Sunday, 30 September 2012

Massive Earthquake deep beneath Columbia.

On Sunday 30 September 2012 slightly after 11.30 am local time (slightly after 4.30 pm GMT) the United States Geological Survey recorded a Magnitude 7.3 Earthquake 162.1 km beneath southeast Columbia, South America. This is a very large Earthquake and could potentially cause a great deal of damage, though its depth should help to mitigate this, since shock waves from quakes lose energy as they pass through rock in any direction - including up. Nevertheless the USGS estimate there is a 61% chance of the quake causing at least one fatality. At the time of writing no casualties or serious damage have been recorded, though people have reported feeling the quake across a large area of southern Columbia and neighboring Ecuador. The quake is not thought likely to be tsunamigenic.

Map showing the areas that suffered the worst shaking during the 30 September quake; greener areas felt more severe shaking than blue areas. USGS.

Columbia is on the west coast of South America and the western margin of the South American Plate, close to where the Nazca Plate, which underlies part of the east Pacific, is being subducted along the Peru-Chile Trench. The Nazca Plate passes under the South American Plate as it sinks into the Earth, this is not a smooth process and the plates repeatedly stick together then break apart as the pressure builds up, causing Earthquakes. As the Nazca Plate sinks further it is partially melted by the friction and the heat of the Earth's interior. Some of this melted material then rises through the overlying South American Plate, fueling the volcanoes of Columbia and neighboring countries.

The passage of the Nazca Plate beneath the South American Plate. Washington State University.


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