Experts point to various factors in explaining 6 temblors in 61/2 months
By Karl Henkel
Thursday night’s earthquake sent shock waves through most of Mahoning County.
The quake wasn’t strong enough to create any damage, but it likely felt a lot stronger than a regular magnitude-2.5 rumble, said Michael Hansen, senior geologist at the Ohio Department of Natural Resources.
That’s because rocks underneath the ground of river valley areas are mostly made up of unconsolidated sediments that amplify ground movement.
“That makes it feel higher intensity,” Hansen said.
That could explain the booming and crashing noises heard by some throughout the Valley.
And although the initial magnitude registered a 2.5, Hansen said follow-up data could revise that number slightly higher.
“It may be 2.6 or a little bigger than 2.6, but not by much,” he said.
Geologists have recorded earthquakes with epicenters in Mahoning County just six times — and all happened in the past 61/2 months.
All have occurred west of the Mahoning River, in close proximity to Salt Springs Road.
The six earthquakes registered magnitudes ranging from 2.2 to 2.6.
According to the Mercalli Intensity Scale, earthquakes between magnitudes 2.0 and 3.0 are felt by a few people, especially those on upper floors.
But why, after a lifetime with no earthquakes centered in Mahoning County, is the area averaging a quake per month?
Experts say there are a few reasons.
“From time to time, earthquakes pop up in Ohio in places where we’ve never had them before,” Hansen said.
One such instance, Hansen said, was in Mentor, near Lake Erie, in 2006.
That region had 14 earthquakes that year and has experienced additional quakes sporadically since.
The source of the Mahoning County quakes are a buried fault of basement rocks, which Hansen estimated could be 800 million to 1 billion years old.
Jeffrey Dick, Youngstown State University Geology Department chairman, said small earthquakes on ancient fault lines aren’t unique, but what’s unusual in Mahoning County is the frequency.
Other geologic movement could be the cause of the Valley’s recent quakes.
“You can get a triggering effect from a large event,” Hansen said, referencing the magnitude-5.8 earthquake registered in Virginia on Aug. 23. “But we had some before that earthquake, so I don’t think that necessarily correlates.”
Hansen also said that the North American Plate is under constant pressure and has “zones of weakness.”
Another outside source has been highly debated within the geology field.
It’s called fracking, a process where water and chemicals are blasted into rocks thousands of feet below the ground to unlock natural oil and gas.
In Ohio and Pennsylvania, companies such as Chesapeake Energy Corp. have begun drilling for natural oil and gas in the Marcellus and Utica shales.
In Harrison County, Chesapeake has drilled one horizontal well 6,418 feet below ground levels, more than one mile deep. Ohio Buckeye Energy has begun fracturing rock in Milton.
Though the Mahoning County earthquakes had a focus more than three miles deep, some geologists, including Michael Blanpied, associate coordinator for the USGS Earthquake Hazards Program, said fracking can lead to tremors.
“That process can cause very small earthquakes,” Blanpied said in video chat on the USGS website after the Virginia quake.
Dick, however, isn’t so sure.
“I think that would be pure speculation, especially when not much fracking has occurred in Ohio,” he said.