Earthquake of M7.1 Strikes in Indonesia, 10 December 2012

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Location of the M7.1 Indonesian earthquake. Image credit: USGS

A large earthquake with a magnitude of 7.1 (M7.1) struck in the early hours of Monday 10 December (Tuesday 11 December, local time) at the eastern end of the Indonesian archipelago.

At the time of writing there were no reports of damage or injury and although the epicentre was offshore, no tsunami warning had been issued.

Witnesses writing on the Volcano Discovery website indicated that the tremor was felt at least 650 kilometers from the epicentre, in Australia.

Tectonic Setting of the Indonesia Earthquake

The epicenter of the earthquake occurred in a highly complex tectonic setting within the general context of the collision between the Australian tectonic plate with the Sunda microplate.

Tectonic information from the USGS indicates that this area is extremely complex geologically, with many different speeds and directions of relative plate movement. Overall, however, the dominant motion of one of convergence. Initial USGS reports suggest that the December 10 earthquake is most likely to have been the result of reverse, or strike-slip, faulting as part of this zone.

An overview of this section of the earth’s crust indicates that there are several different microplates along this convoluted northern margin of the Australian Plate, with regular recent activity taking place along its entire length from the Tonga Trench in the east to the Sunda Trench in the west – a distance of thousands of kilometers which encompasses some of the planet’s most earthquake-prone areas.

Recent and Historic Tectonic Activity in Indonesia

Earthquakes along the northern margin of the Australian plate in the 30 days prior to the 10 December earthquake. Image credit: USGS

The seismically-active nature of this boundary can be clearly demonstrated by looking at the recent record of earthquake activity. A map of tremors of at least M4.0 in the region over the past 30 days shows that the December 10 event is just the latest and largest in a sequence of many dozens of earthquakes along the boundary, with particular concentrations around Tonga and Papua New Guinea.

The USGS map of historic seismicity shows that the area immediately surrounding the most recent tremor has experienced over 20 earthquakes of ≥M7.0 since 1900, two of them being ≥M8.0.

Indonesia Earthquake: Substantial Tremors

Although the seismic activity here is both regular and substantial, it is does not generate mega-earthquakes as regularly as the section of the boundary further west. Here, the subduction of the Indo-Australian Plate beneath Sumatra is the source area for some of the planet’s major and most deadly earthquakes, including the M9.1 Boxing Day earthquake of 2004 and several of ≥M8.0, including two of M8.2 and M8.6 which occurred hours apart in April 2012.

Sources

United States Geological Survey. M7.1 – 227km NW of Saumlaki, Indonesia. (2012). Accessed 10 December 2012

Volcano Discovery website. M7.1 earthquake – 229km NW of Saumlaki, Indonesia. (2012). Accessed 10 December 2012

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