Aceh–Andaman earthquake: What happened and what’s next?

Kerry Sieh writes in Nature:

As the human drama of the Aceh–Andaman earthquake and tsunami unfolded in the last days of 2004, laymen and scientists began scrambling to understand what had caused these gigantic disturbances of Earth’s crust and seas. One of the earliest clues was the delineation, within just hours of the mainshock, of a band of large aftershocks arcing 1,300 km from northern Sumatra almost as far as Myanmar (Burma). This seemed to signal that about 25% of the Sunda megathrust, the great tectonic boundary along which the Australian and Indian plates begin their descent beneath Southeast Asia, had ruptured. In less than a day, however, analyses of seismic ‘body’ waves were indicating that the length of the rupture was only about 400 km.

This early controversy about the length of the megathrust rupture created a gnawing ambiguity about future dangers to populations around the Bay of Bengal. If only 400 km of the great fault had ruptured, large unfailed sections might be poised to deliver another tsunami. If, on the other hand, most of the submarine fault had broken, then the chances of such a disaster were much smaller.

It is sobering to realize that big earthquakes sometimes occur in clusters (for example, seven of the ten giant earthquakes of the twentieth century occurred between 1950 and 1965, and five of these occurred around the northern Pacific margin). Because many of the giant faults in the Aceh–Andaman neighbourhood have been dormant for a very long time, it is quite plausible that the recent giant earthquake and tsunami may not be the only disastrous twenty-first-century manifestation of the Indian plate’s unsteady tectonic journey northward.

Read more here.

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