Magazine article Science News

Coral Clues: Rise and Fall of Reefs Record Quakes' Effects

Magazine article Science News

Coral Clues: Rise and Fall of Reefs Record Quakes' Effects

Article excerpt

Shallow coral reefs around islands west of Sumatra chronicled the uplift and subsidence that resulted from massive quakes that struck that region recently, a new study shows. From data recorded in this biological database, scientists may learn why two undersea ruptures stopped where they did.

On Dec. 26, 2004, a magnitude 9.3 temblor beneath the Indian Ocean spawned killer tsunamis (SN: 1/8/05, p. 19) and a flood of scientific interest (SN: 8/27/05, p. 136). Researchers rushed to the affected region to install sophisticated instruments, many of them in time to record the effects of a magnitude 8.7 quake in March 2005 (SN: 4/2/05, p. 211). But some of the best sensors--the reefs surrounding the region's islands--had been in place all along, says Richard W. Briggs, a geologist at the California Institute of Technology in Pasadena.

Many corals, especially those in the genus Porites, naturally record sea level. They grow to the water's surface but can't tolerate dry conditions for more than a few minutes. Once a mass of corals including those species reaches the sea's surface, it stops growing taller but continues to grow laterally, says Briggs. Thus, a flat top on a Porites colony marks the previous level of a site's lowest fide. Briggs and his colleagues surveyed reefs around islands west of Sumatra to estimate quake-induced rises and falls. They report their results in the March 31 Science.

The two quakes approached the 100-kilometer-long island of Simeulue from different directions. …

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