Saturday, January 08, 2005

Scientific Data on the Indian Ocean Tsunami

As a geologist I probably understand tsunamis better than most but even so the size of the Boxing Day earthquake-born tsunami is difficult to comprehend. To make things worse, the media do little to educate more than our emotions. Natural disasters should remind us all that Nature is much more powerful than humankind and we have little control over such events which are, on a geological time scale, common occurrences.

So, cut away for a moment from the political spats between UN and US, the aid bidding wars between Austraila and Germany, the harrowing scenes of orphans and devastation. NOAA, as usual, provides good factual material, including a map of the epicenter and a schematic movie showing the spread of the tsunami away from the epicenter (speeded up many times).

The first image:

is of the epicenter map. A much larger version can be found here.
The second image:

is from the time lapse movie, also available to download (3.6 MB) from here. This is just after the earthquake and shows a most interesting form. The early shape of the tsunami, probably no more than a ridge of "swollen" ocean out in deep water, is closely aligned to the subduction zone boundary between the Indian Ocean and the Sumatra/Andaman arc. Thus it would appear that the entire subduction zone moved along a length of about 1,000 kilometers.

The important observation from this movie simulation is to explain why the principal damage occurred to the east and west and not to the north and south. This explains why very little damage and loss of life occurred in Bangladesh at the head of the Bay of Bengal, an area that would be expected to funnel the tsunami's energy. See the entire movie and you will understand this better. Bangladesh may have the largest concentration of population living at sea level, so the implication of this movie is profound.

NASA's Earth Observatory website contains additional information on wave height analysis and wave travel time. The highest waves hit Sumatra and are estimated to have been 10 meters high, whereas those hitting Sri Lanka and Thailand were about 4 meters high. Do take a look at other links from this website. A lot of science.