A Magnitude 6.1 Earthquake at a depth of 10 km hit northwest Sumatra slightly after 2.35 pm local time (slightly after 7.35 am, GMT) on Tuesday 2 July 2013, according to the United States Geological Survey. The quake caused building collapses and landslides across Aceh Province, and is known to have killed at least eleven people. Six children were killed and another fourteen are missing after a mosque collapsed in Central Aceh District and five people were killed and two are missing after a landslide and building collapses in Bener Meriah. Over 200 people are believed to have been injured by the event, which was felt as far away as Peninsula Malaysia.
Quake victims recieving treatment outside a community center in Bener Meriah. Ahmad Ariska/Associated Press.
The Indo-Australian Plate, which underlies the Indian Ocean to the west of Sumatra, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Sumatra and neighboring Java, along the Sunda Trench, passing under Sumatra, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fueling the volcanoes of Sumatra.
This does not happen at a 90° angle, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.
The location of the 2 July 2013 Aceh Earthquake. Google Maps.
See also Eruption on Mount Marapi, Sumatra, Indian Ocean shaken by a series of major Earthquakes, Massive Earthquake off Northern Sumatra, 11 January 2012, Large Earthquake in Northern Sumatra and Sumatra shaken by series of Earthquake. 3-4 August 2011.
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