The Tsunami of 26 December 2004

The cause of the tsunami in Sumatra on 26 December 2004 which affected the entire Indian Ocean was a very violent earthquake of magnitude 9.3 on the Richter scale. It was the biggest earthquake ever recorded after the one in Chile on 22 May 1960, with a magnitude of 9.5. It originated at 00:58:53 GMT (7:58:53 AM local time), on a fault in a subduction area between the Indo-Australian plate and the Burma plate (which forms part of the larger Eurasian plate (see fig. 1), with the hypocenter at a depth of about 30 km, 160 km east of Sumatra. The coordinates of the epicentre are: latitude 3° 19' N and longitude 96° E (see green star indicating 2004 in fig. 1). As you can imagine, this a high-risk seismic area. The size of a seaquake depends above all on the extent of the fault on which it occurs and the vertical shift of the sea bed. The fault in question is about 1200 km long (almost as long as Italy), and the shift of the fault varies on average between 5 and 10 metres.
The tsunami took different amounts of time to reach different countries. As we have already said, the speed increases in relation to the depth of the sea, so in deeper waters the wave travelled more quickly. The Tsunami Research Team at Bologna University has calculated how quickly the tsunami propagated (see fig. 2). Areas near the coast are coloured in blue (minimum speed) and areas of open sea are coloured in red (maximum speed) – obviously these latter correspond to the deepest areas of the Indian Ocean.
Could the loss of so many lives have been avoided?
This is the question that the whole world was asking.
The answer is that the number of victims would have been a lot lower if people had been aware of the risks and known about the phenomenon (like the little girl Tilly), and if an alarm system had been installed in the Indian Ocean.
What went wrong?
The PTWC is an alarm system covering almost all the countries of the Indian Ocean. It is made up of a system of seismometers, tide-gauges