The Herald, Sharon,
PA Published Saturday, Nov.. 21, 1998


Earth still quaking, geology major says

By Erin Remai
Herald Staff Writer

The earth moved again, but this time you probably didn't feel it.

Instruments left behind by visiting geologists from the United States Geological Survey, Columbia University and the University of Memphis recorded six aftershocks since the 5.2 quake on Sept. 25.

Katherine Stanley, a junior geology major at Thiel College, Greenville, said the small tremors are normal.

"You can have aftershocks after an earthquake for quite some time," Ms. Stanley said. "It's just the settling process of the earth. It's not an indication that we're going to have a big one."

Seismologists use two different scales to measure earthquakes, the Richter scale and the Mercalli scale.

The Richter scale, according to the World Book Encyclopedia, is the number that indicates the strength of an earthquake. The Mercalli scale divides earthquakes into 12 categories depending on the damage they cause.

For example, the earthquake in Mercer County measured 5.2 on the Richter scale and VI to VII on the Mercalli scale, classifying it as an intermediate earthquake.

The aftershocks all measured 2.3 or below on the Richter scale, or I on the Mercalli scale, meaning only instruments could detect the vibrations.

The Richter scale is exponential. A "5" is 10 times more powerful than a "4", which is 10 times more powerful than a "3". So the main quake here was about 1,000 times stronger than the aftershocks.

Ms. Stanley said the geologists come to town every few weeks to download the data from the seismograph disks, which is why information about aftershocks is not always immediately available.

Ms. Stanley has been studying the quake since the three teams of geologists arrived in Greenville following the earthquake. After her professor, Dr. James Barton, offered the geologists office space and computer equipment, he referred her to them.

"When I came into class the next day he said, 'Go help them,' " Ms. Stanley said. "He sort of drafted me."

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Updated Nov. 21, 1998
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