Wednesday 27 March 2013

Magnitude 6.2 Earthquake beneath Guatemala.

On Monday 25 March 2013, slightly after 5.00 pm local time (slightly after 11.00 pm GMT), the United States Geological Survey recorded a Magnitude 6.2 Earthquake 200 km beneath Guatemala, close to the capitol, Guatemala City. This is a major Earthquake, and would be very dangerous close to the surface, but is not particularly dangerous at this depth since the pressure waves of the Earthquake lose energy as they pass through solid rock. The quake is likely to have been felt over a wide area of the country, as well as in neighboring states Mexico, Belize, Honduras and El Salvador.

Map showing the area over which the 25 March Earthquake was likely to have been felt. USGS.

Guatemala lies on the southern tip of the North American Plate, close to it's boundary with the Caribean Plate, which underlies most of Central America. To the south and west the Cocos Plate, which underlies part of the east Pacific, is being subducted beneath along the Middle American Trench, which follows the coast of Central America at a distance of about 100 km. The Cocos Plate passes under the North American and Caribbean Plates as it is subducted, and this quake almost certainly occurred on the margin of these two plates. Subduction is not a smooth process; the two plates constantly stick together and break apart as the pressure builds up, causing the occasional Earthquake in the process. 

Map showing the tectonic plates beneath Central America. John Elliot/University of Oxford.

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