TECTONICS OF THE INDONESIAN REGION

The plate tectonics of this region, particularly at the eastern end, in the region of the Banda Sea, is perhaps the most complicated of any region in the world. The sharp curve in the Banda Arc is attributed to two distinct dipping slabs. Firstly, we have the Australian plate being subducted under the Asian Plate, and dipping to the north. The strike of this subduction zone is swung around to the north to the east of Timor. To the north of this we have the Pacific Plate, which is being carried to the west by the Tarera-Aiduna Fault, and then being subducted to the south west at the Seram Trough. This interpretation has been clarified by the work of Das ( Journal of Geophysical Reseach, 2004), who has accurately relocated more than 800 earthquakes in the area.

Below - ISC locations from 1964 - 1996 Mag > 4.5 and deeper than 50 km, figure from Das (2004)

for more on tectonics of the Indonesian region, follow this link


GREAT EARTHQUAKE - INDONESIA - 26 Dec 2004

This earthquake was the largest in the world since a Magnitude 9.2 event in Alaksa in 1964. It was the 4th largest event in the world since 1900. It is estimated to have caused rupturing along the plate boundary, in a roughly north-north-west direction, of at least 500 km. The average displacement has been estimated at 15 metres. The zone of aftershocks is at least 1300 km long. As we all know, it caused a tsunami of devastating dimension, having caused deaths as far away as the east coast of Africa.

Minor tsunami effects were recorded on the west coast of Australia, and they are documented elsewhere on this web site.

The current estimate of magnitude is 9.0 ( surface wave magnitude or MS), although some sources have computed a larger magnitude, and it has been suggested that this earthquake was the largest instrumentally recorded earthquake in the world, ever!

The earthquake did not have any foreshocks large enough to be located by international agencies - that is, larger than about magnitude 4.

However, there have been thousands of aftershocks. Up to Jan 14, 2005, there have been 18 aftershocks of magnitude 6 or greater. Five of these were on the same day as the earthquake, four on the following day, and three two days after that. The most recent was on January 9 (as at 14 Jan 2005).

The largest aftershock was a magnitude 7.5 event approximately 3 hours after the main shock.

Follow link for descriptions of the effects of the tsunami in Western Australia


Below - map of all earthquakes in the region, 15 Dec to 14 Jan ( source IRIS)
Readmore ... ( click here )

From: Seismicity of Western Austraia - Indonesia