Good Washington Post Article on Tsunami

The article, In an Instant, the Land Merged With the Sea is a well written merging of different accounts by John Lancaster and Peter S. Goodman. I think it captured everything, and it had some very elusive information in it as well:

...Beneath the sea, mighty geologic plates ground against each other.

One of them was the India Plate, which underlies southern India, Sri Lanka and much of the northern half of the Indian Ocean. The other was the Burma Microplate, part of a complex of small plates lying to the east. While most of the India Plate moves northeast, relative to the Burma Microplate, at the rate of about 2.4 inches a year, the two normally are locked and immobile along the plate boundary -- a fault line that runs roughly north-south off the west coast of Sumatra...

...But the stress along the fault had been building up. It was stored in the rock like a compressed spring. On Sunday morning at approximately 7:58 a.m. local time that spring was released. The lurch unleashed about 200 years of accumulated compression in the course of minutes. The result was an earthquake -- and a massive shift in a rectangle of sea bottom measuring roughly 750 miles by 60 miles, according to estimates by the U.S. Geological Survey.

The plates shifted about 65 feet, of which about 16 feet were in a vertical direction. One part of the fault line reared up, and the other sank down. The displacement of water from that motion created the tsunami.

In contrast to ordinary waves, which are wind-driven surface phenomena, the wave action of Sunday's tsunami involved the entire water column, from the seabed up, experts said. That is a defining quality of tsunamis and one that results in "a lot of energy being transmitted over large distances," according to Ken Hudnut, a geophysicist at the USGS in Pasadena, Calif.

Although the tsunami would have been barely perceptible to passengers on a ship at sea, it rolled outward from the fault zone at about 420 mph, roughly the speed of a commercial jetliner. Even at that speed, however, the surge took about two hours to travel to the Indian mainland.

The tsunami hit coastal areas in different ways. In some places, the first event was the recession of water; in others, it was a flood. The difference was determined at the origin of the tsunami: Along the fault line, the sea floor rose in some places and fell in others. Some coastal areas felt the effect of the sinking first and saw the water recede before it returned, often with a vengeance; elsewhere, the opposite happened. Places farther from the origin of the tsunami, such as Sri Lanka, experienced more waves than did closer areas, such as Sumatra.

As the tsunami approached shallower water near land, its behavior began to change. Its velocity slowed and the distance between its crests, known as wavelength, shortened. The stored energy in the wave was partly transformed into an increase in wave height. What happened next varied widely according to local bottom contours. In some areas, the tsunami broke like a massive beach wave; in others, it caused a sudden, rapid increase in sea level, like water pouring over the edge of a tub...

Read the full article for more.