CHAMPAIGN – Aftershocks have continued from Friday's earthquake.
At 12:38 a.m. today, a temblor of magnitude 4.5 was recorded by the U.S. Geological Survey near Mount Carmel. It was one of more than 20 aftershocks since Friday.
Tim Larson, a geophysicist with the Illinois State Geological Survey, said most modern Illinois earthquakes have had few or zero significant aftershocks.
"This is unusual, but not of concern," Larson said today.
"Just one-third of modern earthquakes in the last 40 years here had significant aftershock sequence," Larson said.
In the previous quake in 1987, he said, "none was big enough to be really felt very far" from the center.
Exactly how many aftershocks have taken place probably won't be known for about a week, when scientists from the University of Memphis and Indiana University working with the state geological survey download data from hard drives in portable seismometers they just set up, Larson said.
"The total number is going to go way up when we have the portable seismometer data," he said.
This morning's aftershock was in the same location – 8 kilometers northwest of Mount Carmel – as Friday's quake, and at the same depth, about 10 kilometers.
That area is part of the Wabash Valley fault system. Exactly how it is related to the New Madrid system is still being researched, Larson said.
Larson said temblors in the range of 4.5 magnitude are "right on the threshold of causing minor damage."