The great Sumatra–Andaman earthquake of 26 December 2004, and the tsunami that it triggered, also shook the geological community. Much scientific effort has since focused on the possibility of further calamitous events in the Bay of Bengal, and especially on understanding the southern stretch of the fault that was responsible for the earthquake, and which lies to the west of the island of Sumatra.
But the fault's northernmost limit, which extends along the coast of Myanmar (Burma) to Chittagong in Bangladesh and faces the densely populated Ganges delta (pictured), has received relatively little attention. Phil Cummins' conclusion that an active zone still exists off Myanmar, as he reports on page 75 of this issue, thus makes for disquieting reading (P. R. Cummins Nature 449, 75–78; 2007).
The Sumatra–Andaman earthquake was triggered when the Indian tectonic plate was thrust violently under the southeast Asian plate off the northwestern coast of Sumatra. Although this subduction zone was known to extend farther north through the Andaman Islands, its location and nature in the Myanmar region were less clear. It had been thought that subduction was no longer active in this area, and that the plate boundary extended, not under the sea, but on the land through Myanmar.
Cummins bases his alternative hypothesis on previous geological studies and recent geodetic measurements, as well as on historical accounts detailing the effects of past earthquakes. He couples these observations with the fact that the floor of the Bay of Bengal has a thick layer of sediments, up to 20 kilometres deep, fanning out from the mouths of the Ganges and Brahmaputra rivers. This 'Bengal fan' insulates the underlying rock, creating thermal conditions more suited to generating earthquakes. Taken together, the implication is that a long, submarine subduction zone stretches for some 900 kilometres from the northern Andamans to the west of Chittagong.
The existence of such a fault requires a thorough re-evaluation of the potential for deadly tsunamis in the northern Bay of Bengal. Cummins' simulation of a large earthquake off the coast of Myanmar and the resultant tsunami shows the devastating effect it could have, and underscores the need for further study and monitoring of rock deformation in this region.