Faulting and the Des Plaines Disturbance

The Des Plaines Disturbance is located mostly in T4N, R12E, Cook County, Illinois. The disturbance is a roughly circular area of approximately 25 square miles that is intensely faulted (Bushbach and Heim 1972). Some of these faults may have as much as 600 feet of vertical movement (Emrich and Bergstrom 1962). The faulted bedrock is buried beneath 75 to 200 feet of glacial drift, and the anomaly can only be studied using well control and seismic reflection data. The Des Plaines Disturbance has been interpreted as a probable meteorite impact structure (Willman 1971).

Seismic reflection data suggest that there are numerous other faults within the bedrock of Cook County. None of these faults are currently active, and the seismic risk to the Chicago area from them is minimal.