Noah Stubbs and Mark Wilson, Evansville Courier & Press
A small earthquake that originated in Southeastern Illinois reverberated around the Tri-State on Tuesday morning, including in Evansville, where residents got a brief shake with their cup of coffee.
Officials with the U.S. Geological Survey say the magnitude-3.8 earthquake was recorded at 6:47 a.m. and was centered near Albion, Illinois, an hour's drive northwest of Evansville.
The depth of the earthquake was reportedly 11.7 kilometers.
The USGS had reports that the temblor was felt as far away as Carbondale, Illinois; Owensboro, Kentucky; Bloomington and Terre Haute in Indiana and farther out.
With a line of storms sweeping through the region at the same time, some in the Tri-State took to social media wondering whether what they felt was a clap of thunder or the ground shaking beneath them.
For a brief few seconds, it was the latter.
Although the ground shaking lit up social media, Mitch Withers, an associate research professor at the University of Memphis, said the 3.8 magnitude temblor wasn't unusual for the area.
"I would classify that as a minor earthquake," he said. "You would have felt minor shaking."
Withers, a faculty member at the university's Center for Earthquake Research and Information, said geological differences explain why the Albion quake would have been felt much farther away than a 3.6 magnitude earthquake reported near Los Angeles Tuesday.
Central United States geology is much simpler compared to West Coast geology, he said, where looser soils and softer, more fractured rock transmit seismic energy more slowly, Withers said.
"The bedrock in Indiana has what is called low attenuation. The seismic energy can travel really far through our bedrock," said Polly Sturgeon, outreach coordinator at the Indiana Geological Survey.
She said the West Coast's geologic conditions act like a sponge to absorb seismic energy.
"An example I like to give is the New Madrid earthquakes of 1811-1812. Those were felt by people as far as Boston," Sturgeon said.
This is the second earthquake to rattle the area in recent weeks. On Sept. 9 a magnitude 3.1 quake was centered west of Mount Carmel, Illinois, according to the USGS.
Not generally considered part of the nearby New Madrid seismic zone to the south, the Tri-State is part of the Wabash Valley seismic zone located in a larger geological area called the Illinois Basin-Ozark Dome Region. It extends from Indianapolis to St. Louis and Memphis, covering parts of Indiana, Kentucky, Illinois, Missouri and Arkansas.
"It's an area known to produce earthquakes and seismic activity," Withers said.
"Moderately frequent earthquakes" occur in the region at irregular intervals, according to the USGS, the most damaging of which was a magnitude 5.4 earthquake in Southern Illinois in 1968.
Withers said it also is not unusual for the area to produce multiple quakes in a short period of time, although not frequently.
He said there is uncertainty about what, if any connection, exists between the Wabash and New Madrid zones.
"We don't understand why we have earthquakes there. It's an area of active research, which is the scientific way of saying, 'we don't know,'" Withers said.
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