Sunday, November 28, 2010

The day after Christmas, 2004

In my memory, the quickest, most abrupt end to a season of holiday cheer came on Dec. 26, 2004, when a monster earthquake killed more than 225,000 people (estimates vary widely.). For most of the victims, it was death by tsunami.

The quake, in the subduction zone off the western coast of the island of Sumatra, began 35 kilometers beneath the surface. Its rupture spread to the northwest at 2-3 kilometers a second for a distance of 1,600 kilometers over five minutes, devastating much of the island and massively displacing Indian Ocean water. The resulting tsunami killed some 200,000 along the northern and western Indian Ocean shoreline - 50,000 died in India and Sri Lanka - and went on to kill others in Africa seven hours after the initial shock.

At a magnitude of 9.3, the quake was the third most powerful ever recorded, equivalent to almost 2 billion Hiroshima bombs. In addition to thousands of aftershocks, it triggered an 8.7 magnitude quake not far to the southeast - itself the 7th-largest on record - set off two volcanoes, and even stirred some volcanic activity in Alaska. Unfortunately, many of the tsunami deaths were unnecessary. Seismologists worldwide knew of the danger within minutes, but (unlike around the Pacific) Indian Ocean countries had no warning system.

If it's any help, the Earth itself took time to mourn the deaths. According to theory, vertical seafloor motions from the quake changed the planet's moment of inertia enough to shorten the length of each day by 2.68 microseconds.

No comments:

Post a Comment