A 3.4-magnitude earthquake in Mifflintown, Juniata County, Wednesday evening was felt as far as Hagerstown, Maryland, according to the United States Geological Survey.
People reported feeling weak to light shaking at about 8:30 p.m. as far north as the Williamsport area, down through central Pennsylvania and into northern Maryland, the USGS’s “Did you feel it?” map shows. According to social media posts, people heard or felt the quake throughout Centre County, including Ferguson Township, Boalsburg, Bellefonte and State College.
Wednesday evening’s quake was the first of its magnitude in central Pennsylvania since 1991 in Centre Hall, Penn State professor of geoscience Andy Nyblade said. Nyblade is part of the team at the university that runs the Pennsylvania State Seismic Network.
Prior to Wednesday, the largest earthquake near Mifflintown had been a 2.5 magnitude in 1991, near Mount Union, Huntingdon County, data from the PASEIS website show.
Although the reason why an earthquake of that magnitude occurred in an area where those types of quakes have historically been infrequent is unclear, Nyblade said that the depth of the quake — 26.2 kilometers — suggests it was likely due to natural causes.
“It was deep in the Earth’s crust, so it’s clearly not associated with fracking or explosions at the surface,” he said.
Because of its depth, Nyblade said it was also hard to correlate it with any faults mapped at the surface, because those faults might not extend that deep.
One 1.2-magnitude aftershock was recorded on the Pennsylvania State Seismic Network at 9:30 p.m. Thursday. The aftershock was 31.4 kilometers deep, and recorded a few miles northwest of the original quake.
Nyblade said that as far as he knew, there have not been any reports of property damage from the earthquake. Given the size and depth, he said he’d be surprised if there were.