Digital News Report – Illinois residents experienced a small 3.8 magnitude earthquake on Wednesday at around 3:59 AM (1:59 AM Pacific). It was centered about 3 miles south-southwest of Pingree Grove, IL and just 20 miles north-northwest of Aurora, IL.
The U.S. Geological Survey says Chicago residents may have felt the tremor. Chicago was just 30 miles east-southeast of the epicenter. The depth of the quake was 8.6 miles below the surface of the earth.
It is uncertain whether this was a pre-shock of a bigger event to come, but earthquakes in this area are rare. In fact, earthquakes east of the Rocky Mountains are rare, but when they do occur they are usually small and felt over large areas. Quakes can be felt 10-times as far east of the Rockys as they can be felt to the west, the USGS reports.
The fault which caused the quake has not been identified. It is believed to be “un-named”, so this may be a new one. Most identified fault lines are found west of the Rocky Mountains.
“Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most of the region’s bedrock was formed as several generations of mountains rose and were eroded down again over the last billion or so years,” the report stated.
The known seismic zones east of the Rocky Mountains include the New Madrid zone centered on southeastern Missouri, the Saint Lawrence rift system, the Charlevoix-Kamouraska seismic zone of eastern Quebec (large quake in 1925). Earthquakes can also occur in New York, Philadelphia, and along the Wilmington urban corridor.
By: Sam Lee
Continental divides of North America include the so-called Great Divide, the Northern Divide, the Eastern Divide, and the St. Lawrence Seaway Divide.