The United States Geological Survey detected a Magnitude 4.7 Earthquake at a depth of 25.4 km in the Sierras de Córdoba, a mountain range in Córdoba Province in central Argentina, slightly before 10.45 pm local time on Wednesday 11 September 2013 (slightly before 1.45 am on Thursday 12 September, GMT). There are no reports of any damage or casualties arising from this quake, though it was felt as far away as the city of Córdoba, slightly over 50 km to the northeast of the epicenter.
The approximate location of the 11 September 2013 Sierras de Córdoba Earthquake. Google Maps.
The Sierras de Córdoba are an ancient mountain range, formed by the subduction of an ancient oceanic plate beneath the continent of Gondwana during the Palaeozoic and now much eroded. This ancient subduction is unlikely to be the cause of this Earthquake, however, with the modern subduction of the Nazca Plate beneath South America being a more likely explanation.
The Nazca Plate beneath the southeast Pacific Ocena is being subducted beneath the South American Plate, causing quakes in a number of ways. Firstly there is friction between the two plates as the Nazca Plate passes under South America. Then there is crumpling and upthrust of the South American as it is pushed from the west by the Nazca Plate and from the east by the expansion of the Atlantic. Finally there is volcanic activity in the Andes, as lighter minerals in the Nazca Plate are melted by the heat of the Earth's interior, then rise up through the overlying South American Plate to form volcanoes.
See also Magnitude 4.4 Earthquake on the Altiplano Plateau in northwest Argentina, Magnitude 4.2 Earthquake in northern Chile, Deep Magnitude 4.5 Earthquake in northwest Argentina, Evacuations ordered after activity on Copahue and Eruption on Mount Copahue.
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