Derry Township tremor reclassified as mine collapse
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If an earthquake happens and nobody feels it, did it really occur?
Not if it turns out to be a mine collapse.
According to the U.S. Geological Survey, a 2.9-magnitude tremor early Tuesday, centered in an area east of Gray Station Road in Derry Township, was actually the collapse of multiple mine pillars.
The mine subsidence collapse happened in an abandoned section of the Hanson Torrance Quarry near Bolivar, said Lauren Fraley, a spokeswoman with the Pennsylvania Department of Environmental Protection.
“This is a DEP-permitted active underground limestone mine, but the roof fall is in an abandoned area,” Fraley said. “DEP will continue to monitor roof movement through the coming days.”
All mining activity is stopped, Fraley said. The DEP also issued a compliance order that prevents any mining until further notice.
A Westmoreland County 911 supervisor said the department did not receive any calls related to the collapse, and that local emergency responders in the area were not aware of it until county 911 officials reached out on Tuesday afternoon.
Fraley said the DEP is not aware of anyone injured in the collapse.
“We originally put it out there as an earthquake, then did some digging into it and determined it was a collapse,” said Don Blakeman, a geophysicist with the USGS. “Sometimes it’s hard to tell precisely what an event is just by looking at a waveform.”
A 2.9-magnitude quake is classified as a minor quake on the Richter scale, felt slightly by some people but rarely causing damage to buildings.
More than 1 million such quakes happen annually, according to the USGS. An earthquake of similar magnitude was reported nearly a year ago — Oct. 15, 2019 — about 6 miles southwest of Washington, Pa.
County Emergency Management Coordinator Roland Mertz said he received a phone call about the USGS’s initial quake declaration Tuesday afternoon from the Pennsylvania Emergency Management Agency.
“Once we found out, we notified the Fairfield Township emergency coordinator, and he said he was in bed and never felt anything at all,” Mertz said.