A Tsunami Devastates the Indian Ocean Coasts

On the morning of 26 December 2004, a massive undersea megathrust earthquake ruptured along the boundary between the Burma plate and the Indian plate off the western coast of northern Sumatra. The rupture began at a depth of about thirty kilometres and spread northward for some 1,200 to 1,300 kilometres over several minutes. This event, known scientifically as the Sumatra-Andaman earthquake, produced seismic oscillations felt across the entire planet. While early seismological reports rated the shock at magnitude 8.8, subsequent research placed its moment magnitude between 9.1 and 9.3, making it one of the largest earthquakes ever recorded by modern instruments.

The physical displacement along the fault zone involved massive vertical uplift of the seafloor by several metres, which abruptly displaced the overlying ocean water and transferred extraordinary amounts of energy into the surrounding sea. Because the rupture ran along a predominantly north-south axis, the resulting waves radiated outward most powerfully toward the east and west. In deep water, the tsunami traveled at speeds reaching hundreds of kilometres per hour as a barely discernible swell, but as the surge encountered shallow coastal contours, it slowed and reared into towering crests, with runup heights of more than thirty metres observed along the west coast of Sumatra.