Thursday 8 November 2012

Earthquake off the coast of Guatemala.

On Wednesday 7 November at 10.35 am local time (4.35 pm, GMT) the United States Geological Survey recorded a Magnitude 7.4 Earthquake at a depth of 41.6 km, roughly 17 km off the southern coast of Guatemala. This is an extremely large and very dangerous event; the USGS estimate that fatalities from a quake this large in this area are almost unavoidable. The quake is known to have caused buildings to collapse across a wide area of southern Guatemala, and 48 people are known to have died at the time of writing (16 hours after the event). The US National Oceanic and Atmospheric Administration issued a tsunami warning for areas of the east Pacific, but in the event only a small wave was observed.

Map of the southern coast of Guatemala showing the areas that underwent the most severe shaking. Areas coloured yellow are likely to have seen damage to buildings. USGS.

Guatemala is located on the southern part of the Caribbean Plate, close to its boundary with the Cocos Plate, which underlies part of the east Pacific. The Cocos Plate is being pushed northwards by expansion of the crust along the East Pacific Rise, and is subducted beneath the Caribbean Plate along the Middle American Trench, which runs parallel to the south coast of Guatemala and neighboring countries, passing under Central America as it sinks into the Earth's interior. This is not a smooth process, the plates tend to stick together, breaking apart again once the pressure from the northward movement of the Cocos Plate builds up to much, triggering Earthquakes. As the Cocos Plate is subducted further into the mantle it is heated by the friction and the heat of the planet's interior, causing it to partially melt. Some of the melted material then rises through the overlying Caribbean Plate, fueling the volcanoes of Central America.

Diagrammatic representation of the subduction of the Cocos Plate beneath the Caribbean Plate along the Middle American Trench. VCS Mining.

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