A major earthquake, with a magnitude of 7.7, struck of the southern coast of the island of Sumatra on 25 October 2010 ( United States Geological Survey “Magnitude 7.7 - Kepulauan Mentawai Region, Indonesia” earthquake.usgs.gov). The earthquake occurred in the same region as the Boxing Day earthquake of 2004, though some 800 miles further south.
The Earthquake of 25 October 2010
Information from the United States Geological Survey indicated that the earthquake, which took place at around twenty minutes to three in the afternoon local time, occurred offshore at a depth of around 13 miles. The epicentre was approximately 150 miles west of Bengakalu and 175 miles south of Padang. The tremors were reportedly felt as far away as Singapore and Thailand.
The quake was followed by several major aftershocks, at least two of which had a magnitude of over 6.0 on the Richter scale, sufficient for them to be considered major seismological events in their own right. A tsunami warning was issued but was lifted shortly afterwards, although CNN reported that a 3m high tsunami occurred in some areas ( CNN “At least 40 dead, 380 missing after Indonesia quake” 26 October 2010 edition.cnn.com).
Given the nature of the terrain nearest the epicentre, which includes many remote islands, early information on the number of casualties in unclear. At the time of writing, reports indicated that at least 40 people were killed and around 400 so far reported missing, including the passengers and crew of a tourist boat. It seems likely that this figure will increase.
Other Major Earthquakes along the Sunda Trench
Sumatra is one of the most seismically active parts of the world, being located at a boundary between two of the earth’s tectonic plates. The boundary is defined as a destructive boundary, where one plate (in this case the Australian Plate) is being dragged downwards below another (in this case the Sunda Plate) causing a deep trench beneath the ocean. The relative movements of these two plates create immense pressure, which is then released in the form of earthquakes.
Sumatra is best known to the public as the location of the major Boxing Day earthquake of 2004, which is thought to have claimed over a quarter of a million lives (USGS). The October 25 earthquake and its major aftershocks are part of a series of major earthquake events to have taken place in the area.
The Boxing Day earthquake is one of the largest on record, with a magnitude of 9.1. It was followed by events with magnitudes of 8.5 in 2005 and 7.5 in 2009. Previously, major earthquakes with estimated magnitudes of around 8.8 occurred in 1797 and 9.0 in 1833, although none of these caused devastation on the scale of that which occurred in 2004.
Several smaller earthquakes have also occurred. USGS figures indicate that the region had experienced almost 40 earthquakes with a magnitude greater than 6.0 between Boxing Day 2004 and October 2010. Three of these have reportedly had a death toll of over 1,000. The area is also characterised by high levels of volcanic activity, most notably the catastrophic eruption of Krakatoa in 1883.
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