Sunday 27 November 2016

Magnitude 7.0 Earthquake off the coast of El Salvador.

The United States Geological Survey recorded a Magnitude 7.0 Earthquake at a depth of 10.3 km, roughly 149 km offshore of the municipality of Puerto El Triunfo in Usulután Department, El Salvador, slightly before 6.45 pm local time on Thursday 24 November 2016 (slightly before 0.45 am on Friday 25 November, GMT). The quake was felt across much of Central America, from Guatemala to Costa Rica, though there are no reports of any major damage or injuries. A tsunami warning was initially issued, but later withdrawn.

The approximate location of the 24 November 2016 Central American Earthquake. Google.

El Salvador and the other countries of Central America are 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 Central America, passing under the peninsula  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. 

Earthquakes along subductive margins are particularly prone to causing tsunamis, since these often occur when the overlying plate has stuck to the underlying plate, being pulled out of shape by its movement.. Eventually the pressure builds up to far and the overlying plate snaps back, causing an Earthquake and a tsunami. 

Simplified graphic showing tsunami generation along a convergent margin.NASA/JPL/CalTech.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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