August 23, 2011

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Bucknell seismograph

By Julia Ferrante

LEWISBURG, Pa. -- The 5.8 magnitude earthquake that rocked Virginia Tuesday afternoon and was felt in states stretching from North Carolina to Massachusetts also registered 216 miles away at Bucknell University's seismic station.

Rob Jacob, an assistant professor of geology at Bucknell, said the quake occurred at 1:51 p.m. along a reverse fault line near Charlottesville, Va., when the earth's crust shifted due to compressive forces.

"This was likely a violent rupture followed by sliding, distributing energy in all directions," Jacob said, explaining that a fault is a location of weakness within the earth's crust where the rocks can break apart suddenly and cause displacement. "Earthquakes in this part of the world are relatively rare, but there is evidence of historic seismicity."

Although the earthquake epicenter was far from Lewisburg, the old and cold rocks of the Appalachians transmitted the seismic energy with little attenuation, which is why the earthquake was felt at Bucknell, said Mary Beth Gray, an associate professor of geology.

Gray said the intensity felt in Lewisburg was about 3 on a 12-point scale, which indicates slight shaking, according to the USGS.

"The maximum intensity, as reported by citizens logging onto USGS website, was 7 on the same 12-point scale," Gray said. "That represents very strong shaking and may have produced moderate damage. Approximately 300 earthquakes of this magnitude happen worldwide annually."

The Bucknell seismograph, which is in the basement of the Carnegie Building, recorded the event. The community is welcome to view the display in the first-floor hallway of the O'Leary Building. Those who felt the earthquake are encouraged to report their observations on the USGS website.

Contact: Division of Communications


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