The Herald, Sharon,
PA Published Sunday, Sept. 26, 1999


Scientists discover facts of the quake

By Erin Remai
Herald Staff Writer

The Sept. 25, 1998, earthquake that rocked Mercer County not only stirred up excitement on the local front, it caught the attention of scientists all over the country.

Within hours of the original 5.2 magnitude quake, named the Pymatuning earthquake due to its proximity to the Pymatuning reservoir, seismologists, geologists and geophysicists arrived from Columbia University, the University of Memphis and the United States Geological Survey in Golden, Co. and placed 12 portable seismographs around the earthquake's epicenter near Jamestown.

These scientists, along with hydrogeologists Gary Fleeger and Dennis Risser, Thiel College student Katherine Stanley and several other scientists contributed their research to the winter 1998 edition of Pennsylvania Geology, published by the Bureau of Topographic and Geological Survey in Harrisburg.

On the local scene, Ms. Stanley, now a senior at Thiel, used her field work during the earthquake as part of her senior research project. Ms. Stanley sent out a survey to Thiel alumni asking them if they felt the earthquake and how it felt to them.

"I got a very good response," Ms. Stanley said. "I took the data and transferred it to a map, similar to what the USGS was doing, but I based it on Thiel."

Ms. Stanley said the last of the seismographs left the area the first week of December and that her study is just about complete. She said she eventually wants to turn the personal anecdotes about the earthquake that she's collected over to the Greenville Historical Society.

"Maybe 100 years from now people can look at personal views (on the earthquake)," she said.

According to Pennsylvania Geology, at least 11 aftershocks have occurred since March 1999, the largest being a magnitude 2.3, too small to be detected without instruments.

But the most visible result of the earthquake was the loss of well water and the formation of new artesian wells and springs.

"The most important result of the earthquake was the water well damage," said Edward Cranswick, geophysicist for the USGS in Golden, Co. He and his team, who recently returned from field work in Turkey, gave a presentation in June in Boston on the Pymatuning Earthquake.

"We obviously documented a lot of wells that had gone dry," said Risser, who works for the USGS in Lemoyne, Pa. "Water levels continued to go down through the spring and summer."

According to the USGS publication "The Hydrologic Effects of the Pymatuning Earthquake of Sept. 25, 1998 in Northwestern Pennsylvania," the location that experienced the most problems with lost well water is a ridge about five miles long and two miles wide between Greenville and Jamestown.

Pennsylvania Geology describes this area as a "hydrologic island," in which groundwater is trapped by bedrock. Each "island" has its own groundwater flow system and is isolated from groundwater flows in adjacent "islands."

Risser said that the earthquake either created new fractures or opened up old fractures in the bedrock, which allowed the groundwater to escape to lower-lying valleys, which created new streams and artesian wells.

The Herald reported on Oct. 27 that a USGS observation well had risen two to three feet and remained at that level after the earthquake; a supposedly dry well in a Sugar Grove Township basement started flowing; and a spring-fed pond, also in Sugar Grove Township, filled within a few hours of the quake. These events were also documented in "Hydrologic Effects."

Risser said that some studies show that the fractures may heal or clog up with precipitants over time and the shale will once again prevent the downward flow of groundwater.

Fleeger, the principal author of "Hydrologic Effects," said he's not sure if the hydrologic changes caused by the earthquake are permanent.

"There was some work done in California with similar changes that suggest the groundwater would return to its original level," said Fleeger, who works for the Pennsylvania Bureau of Topographic and Geologic Survey. "California has so many earthquakes they would have run out of groundwater long ago."

Both Risser and Fleeger said it's difficult to determine what will happen with the groundwater because they don't have past examples to compare to.

"We didn't have a lot of measurement before the earthquake. We had to talk to well drillers and homeowners about what the levels were before the earthquake," Risser said. "We didn't have a lot of concrete data to go on."

Fleeger said he continues to check groundwater levels every month for signs of recovery.

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Updated Sept. 27, 1999
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