M 9.3 Earthquake - Decemer 2004, Indonesia

On 26 December 2004 at 00:58:49 (UTC) an earthquake with Moment Magnitude 9.3 struck offshore, close to the northwest coast of Sumatra. This was the largest seismic event since the great Alaskan earthquake of 1964, and triggered an ocean-wide tsunami that claimed more than 230,000 lives in 15 countries¹.

The earthquake occurred where the Indo-Australian Plate to the west and south is subducting at about 7 cm per year beneath the Eurasian Plate, to the east and north. The zone of convergence comprises three fault segments known as the Andaman, Sunda and Timor thrust zones. The 2004 event ruptured the entire (1200 km) Andaman Thrust causing violent shaking that lasted for eight minutes in the Aceh province of Indonesia¹,² as the rupture propagated northwards from the initial rupture off northern Sumatra³. The earthquake released almost two centuries of strain, causing vertical and horizontal displacements of the coast and sea-floor that triggered the resulting tsunami⁴. The earthquake itself (apart from the tsunami) was felt as far away as Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore and the Maldives⁵.

In the 48 hours following the main shock, 31 aftershocks shook the region, with Richter Magnitudes ranging from 5.5 to 7.3¹.

¹ Sinadinovski, C. 2006. The Event of 26th of December 2004: The Biggest Earthquake in the World in the Last 40 years. Bulletin of Earthquake Engineering. Vol. 4, pp 131-139

² BBC News. 2005. Tsunami: Anatomy of a disaster
http://news.bbc.co.uk/1/hi/sci/tech/4381395.stm

³ Subarya, C, Chlieh, M, Prawirodirdjo, L, Avouac, J-P, Bock, Y, Sieh, K, Meltzner, A.J, Natawidjaja, D.H & McCaffrey, R. 2006. Plate-boundary deformation associated with the great Sumatran-Andaman earthquake. Nature. Vol. 440, pp 46-51

⁴ Hopkin, M. 2005. Triple slip of tectonic plates caused seafloor surge. Nature. Vol. 433, pp 3

⁵ Wikipedia. 2007. 2004 Indian Ocean Earthquake
http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake