Scientists are trying to explain a 3.3 magnitude earthquake that struck 13 miles southeast of Battle Creek, Michigan Wednesday.

The quake was recorded 20 miles from the epicenter of a 4.2 magnitude earthquake that struck on May 2nd, the strongest recorded in Michigan in 67 years.

The Wednesday quake was far enough apart from May’s quake that scientists say it’s not an aftershock of the first.  Apparently there are two separate fault lines in the region. The first quake revealed a fault line that had only been previously speculated by scientists but had not been proven.

“After the May event, I suspected we wouldn’t see another event, so I was a bit surprised by this one,” said Harley Benz, a seismologist with U.S. Geological Survey (USGS). “What more surprised me is that they weren’t in the same locations.”

John Yellich of the Michigan Geological Survey concurred the two quakes were not connected.

“Two separate ones today. That’s what it looks like,” Yellich said. “Nothing unusual and the fact that we are getting two of them in the same area, it could be that it’s all of this movement just readjusting. It appears to be two different areas.”

Benz said the quakes could be “glacial rebound”, a conditions where land masses pressed down by tons of ice during Michigan’s last glacial period are starting to rise.

While some environmentalists were quick to related the quakes to the process known as “fracking”, Benz said that evidence shows the quakes are tectonic, or related to the natural movements of the earth’s crust.