Magazine article Oceanus

Tsunami Leaves Behind Intriguing Clues

Magazine article Oceanus

Tsunami Leaves Behind Intriguing Clues

Article excerpt

Is a domino effect operating along faults in the Indian Ocean?

If any good has come from the devastating earthquakes off Sumatra, it is that they are providing scientists with unprecedented clues to learn how large undersea earthquakes occur and how they create tsunamis.

In the wake of the catastrophic earthquake and tsunami on Dec. 26, 2004, and a subsequent magnitude 8.7 quake on March 28, 2005, scientists have gathered new information to answer provocative questions: Did the Dec. 26 earthquake shift stress in the Java Trench where the earthquakes occurred and help trigger the March 28 quake? Was the Dec. 26 quake shallow, and did this contribute to generating such a great tsunami? Why did the March 28 quake generate only a minor tsunami even though it was a great quake?

The earthquakes occurred in a subduction zone where two of Earth's great crustal plates are colliding. As one plate is thrust beneath another to form the deep Java Trench, it causes the buildup of stress in rock formations, which slip suddenly to generate earthquakes.

Jian Lin, a marine geophysicist at Woods Hole Océanographie Institution, and his colleague Ross Stein of the U.S. Geological Survey in Menlo Park, Calif., have investigated thrust earthquakes both on land and under the oceans for several years. In a study published in early 2004, the two scientists theorized that as thrust earthquakes alleviate stress in one region, they can shift that stress to adjacent areas.

In a domino-like effect, stress can transfer through the crust to interact with neighboring faults and trigger another earthquake elsewhere. Lin and Stein noted that such a domino-like reaction appears to have occurred in a series of moderate-sized thrust quakes in central California in the 1980s.

Is the domino-like reaction also occurring in the Java Trench? Recently several research groups calculated that the Dec. …

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