26 December, 2004: Tsunami

It was one of the strongest earthquakes ever to be recorded - with a magnitude of at least 9 it is probably the fourth strongest event known in modern history, it shook even the rotation axis of earth and raised the bottom of the Indian Ocean by 5m. But the quake itself generated less destruction; it was the resulting wave - a Tsunami reaching 10 to 15m height on the coats of Sumatra, the nearest landmass from the epicentre.

Fig.1. Simplified Structural Map of Sumatra with the epicentre of the Boxing Day earthquake 26.12.2004.
Note the Accretionary Wedge formed by the the Indian Ocean subducting beneath the southwestern margin of the Sundaland Craton. The deformation front of the Sumatran subduction system is indicated by the toothed line; spreading centres and transform faults are shown (from BARBER et al. 2005).

Sunday 26 December 2004 was a sunny day on the Indonesian island of Sumatra; the coast soon became frequented by tourists and locals. 15 minutes after the earthquake, at 8:14 the first wave reached the coast. The sea level first regressed and then suddenly a huge wave approached.
The force of the water tore away much of the buildings in its way and carrying with it debris caused a swath of destruction. The first wave cleared the path for the second one, that even faster demolished the interior areas of the coast.
The wave travelled for 8 hours trough the entire Indian Ocean, bringing destruction and death to the coasts of Indonesia, Thailand, Sri Lanka, India, Somalia, Kenya, Tanzania, Madagascar and flooding the smaller islands in the Indian Ocean.

The death toll raised and raised in the following hours and days after the catastrophe - finally estimation counted more than 300.000 fatalities, possibly thousands of bodies remain either lost to the sea or unidentified, thousand of people injured, large coast areas devastated.

Bibliography:

BARBER, A.J.; CROW, M.J. & MILSOM, J.S. ed. (2005): Sumatra - Geology, Resources and Tectonic Evolution. Geological Society Memoir No. 31: 304