Sunday 20 September 2015

Fourteen confirmed deaths after Magnitude 8.3 Earthquake off the coast of Chile.

Fourteen people have now been confirmed dead following an Earthquake off the west coast of Chile on Wednesday 16 September 2015. The event happened slightly before 6.55 pm local time (slightly before 10.55 GMT) and was recorded by the United States Geological Survey as being a Magnitude 8.3 event at a depth of 25 km. The Earthquake itself caused relatively little damage, but triggered a tsunami that was felt around the Pacific basin and was almost 5 m high when it struck parts of the coast of Chile. It is thought that the number of casualties will still rise further, though a much higher number of deaths was avoided by prompt evacuations of low lying areas.

Tsunami damage in the city of Coquimbo on Thursday 17 September 2015. AP.

In addition to the thirteen confirmed fatalities in Chile one person is reported to have died in Argentina (an elderly man who fell down a flight of stairs in Buenos Aries during an evacuation). A further eleven people are known to have sustained serious injuries, and 262 homes are known to have collapsed in Chile and a further four in Argentina, while 420 homes were rendered uninhabitable due to damage in Chile and 82 in Argentina. Chile has also received significant damage to infrastructure, with over 14 000 people left without power and over 9000 without water in Chile, and damage to a number of civic buildings recorded in Argentina.

The approximate location of the 16 September 2015 Chilean offshore Earthquake. Google Maps.

Chile is located on the west coast of South America, which is also the convergent margin between the Nazca and South American Plates. The Nazca Plate is being subducted beneath the South American Plate and is sinking beneath the South American Plate. This is not a smooth process, the rocks of the two plates continuously stick together then, as the pressure builds up, break apart again, causing Earthquakes. As the Nazca Plate sinks deeper it is partially melted by the heat of the Earth's interior. Some of the melted material then rises up through the overlying South American Plate as magma, fueling the volcanoes of the Chilean Andes.

The subduction of the Nazca Plate beneath the South American Plate, and how it causes Earthquakes and volcanoes. Pacific Earthquake Engineering Research Center.

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 tp 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 organization 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.

The times at which the tsunami caused by the 16 September 2015 earthquake reached different parts of the Pacific Basin. National Tsunami Warning Center.

See also...

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