Magazine article Science News

Powerful Quake Shakes South Pacific

Magazine article Science News

Powerful Quake Shakes South Pacific

Article excerpt

Powerful Quake Shakes South Pacific

A scant six hours after a severe earthquake shook the seafloor southwest of New Zealand last week, seismologists had sketched a portrait of the fault fracture that generated this quake, the Earth's largest in at least 12 years.

"This is sort of the beginning of a new era in seismology," says Harvard University's Adam M. Dziewonski. "We have a nearly real-time capability to assess not just quake location -- which has been done for a long time -- but also the mechanism and the type of forces."

The May 23 earthquake, measured at 8.2 to 8.3 on the Richter scale of magnitude, struck along the Macquarie ridge about 500 miles from New Zealand. "It was an extremely large earthquake. But it was just out in the middle of nowhere and there appears to be no damage," says Bruce W. Presgrave from the U.S. Geological Survey's National Earthquake Information Center in Golden, Colo.

Seismologists define the geologic structures that produce quakes by analyzing seismic waves traveling through the Earth. Among other things, the waves indicate whether horizontal or vertical motion caused the quake and characterize the orientation of this motion. To perform these calculations, seismologists usually must wait several months for seismic data from stations around the world to reach large information networks.

Dziewonski and his colleagues cut this time to hours by retrieving digital data from two seismic stations on either side of North America via computer modems -- his group's first opportunity to test the technique on such a large quake. Researchers at the University of Paris and at the California Institute of Technology in Pasadena use the same process.

Based on limited data, these estimates serve only as first approximations but can provide important information. …

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