Aftershocks
A week after the main earthquake, the USGS recorded a total of 26 aftershocks ranging in magnitude from 1.0 to 4.6. The biggest aftershock occurred at 10:14am CDT (15:14 UTC), on April 18; it was a magnitude 4.6, and also centered near West Salem, just north of the original quake. An aftershock with a magnitude of 4.0 (initially reported as 4.5) was felt three days later on April 21, at 12:38am CDT (05:38 UTC), centered northwest of Mt. Carmel, Illinois. A 3.7 aftershock struck on Friday, April 25 around 17:30 GMT (12:30 PM CDT). A 3.3 aftershock struck on Thursday, May 1 around 5:30 GMT (12:30 AM CDT). A 3.6 aftershock struck on Thursday, June 5 around 2:13 AM local time.
Read more about this topic: 2008 Illinois Earthquake