Tuesday 28 August 2012

Large Earthquake off the south coast of El Salvador.

On Sunday 26  August 2012, slightly after 10.35 pm local time (slightly after 4.35 am on Monday 27 August, GMT), an Earthquake occurred roughly 100 km off the south coast of El Salvador, which the United States Geological Survey recorded as measuring 7.3 on the Richter Scale, at a depth of 20.3 km. This is a substantial quake, and quite shallow, so even though it is some way offshore , the USGS estimate that there is a 35% chance of this quake leading to fatalities. The Pacific Tsunami Warning Center issued a warning for this quake, but the wave generated was apparently only 20 cm high when it reached Central America; unlikely to have caused anyone serious problems.

Map showing the location of the 26 August quake, and the areas worst hit by shaking. The quake would have been felt by most people inside the outermost circle, and there is a risk of damage to buildings within the next circle, which touches the coast of El Salvador. USGS.
This quake was followed by a large number of aftershocks, some of which exceeded magnitude 5.0, adding to the hazard caused by this event.
Map showing recent seismic activity off the south coast of El Salvador. Each square represents a separate quake, with larger quakes represented by larger squares. The yellow squares occurred earlier in the week, the red square is the most recent event. The red line is the Middle American Trench. USGS.
El Salvador, and neighbouring Central American states, lies on the Caribbean Plate. To the south of Central America the Coccos Plate, which underlies an area of the east Pacific, is being subducted beneath the Caribbean Plate along the Middle American Trench. As the Coccos Plate is drawn under Central America is causes friction (Earthquakes), which combined with the heat of the planets interior, slightly melts the plate, producing liquid magma, some of which then rises through the overlying Caribbean Plate, fuelling the volcanoes of Central America.
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