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Quake a no-show for encore

Seismologists went to Mercer County in hopes of measuring a rare earthquake's aftershocks

Friday, October 02, 1998

By Byron Spice, Science Editor, Post-Gazette

Three teams of seismologists raced to northern Mercer County last weekend in hopes of making precise measurements of aftershocks from Friday's earthquake, the most intense ever recorded in Pennsylvania.

But as of yesterday, it was all for naught. None of the seismometers they installed around the quake's epicenter detected any tremors from an aftershock.

"Unfortunately for us, it's been a very quiet week," said Stephen Horton, a seismologist at the University of Memphis.

One of the teams, from Columbia University, has already packed up for home, and seismologists from the U.S. Geological Survey are expected to follow shortly.

The epicenter of Friday's earthquake, which registered 5.2 on the Richter scale, appears to have been about 3.1 miles below ground at Turnerville, about 15 miles north of Sharon. Waverly Person, a geophysicist at the U.S. Geological Survey's National Earthquake Information Center in Colorado, said the seismologists had hoped to record two or three aftershocks, perhaps with a magnitude of 3 or 4, which would help them to better determine the depth of the focus of the quake.

This isn't something they would normally do for an earthquake in the western United States, where temblors often are associated with fault lines at the surface. In the East, however, most earthquakes, like the Mercer County quake, emanate from zones of crustal weakness that are buried deep.

That makes it hard to pinpoint the epicenters of these quakes. And that's why last week's moderate-size quake had scientists hoping that the aftershocks would give them a better idea of just where it came from.

The teams have had some scattered reports of aftershocks from area residents, said Horton, who set up shop at Thiel College in Greenville. But such reports usually are unreliable unless a half dozen or more people nearby also report feeling the shocks, he noted.

Aftershocks aren't necessarily a given, Person said, and the more time passes without one, the less likely it becomes that any aftershock of any useful size will occur.

Without further help from Mother Earth, scientists are turning to area residents and the Internet in hopes of finding the quake's source.

The Memphis researchers are asking people to visit their Web site and answer questions about where they were at the time of the quake and whether they felt it. A questionnaire on the site asks people to say when they felt it, how long the shaking lasted and whether it caused chandeliers to swing or dishes to fall off shelves.

"It will give us an idea of how intense the quake was," Horton said. "In the absence of any aftershock, this is our next best chance to find its focus."

The Web site address is:

No injuries have been reported from the quake and damages appear to be few. Person said at least three chimneys near the epicenter tumbled, but gas and water pipes remained intact. He attributed the lack of damage largely to the fact that the epicenter was in a rural area.

"If this had occurred in a city, you would have seen more damage," he added.

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