Quake details, from the USGS. Of note: quake depth was 3.1 miles...relatively shallow depth. This is a mid plate area, clear of the NewMadrid sweep zone. Testing was done in this area (closer to Chicago, P wave and Short Wave seismic tests) back in 2001 for structural safety of Chicago building zones.
Gilberts is at the northern edge of Kane county...that's close to the Wisconsin border. The seismically active region of Illinois is in the southern portion of the state, relevant to the NewMadrid lines.
This is indeed a very unusual place for a quake.
http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010snay/Magnitude 3.8 - ILLINOIS
2010 February 10 09:59:33 UTC
Earthquake Details
Magnitude 3.8
Date-Time
* Wednesday, February 10, 2010 at 09:59:33 UTC
* Wednesday, February 10, 2010 at 03:59:33 AM at epicenter
* Time of Earthquake in other Time Zones
Location 42.053°N, 88.412°W
Depth 5 km (3.1 miles) set by location programRegion ILLINOIS
Distances
* 2 km (1 miles) SSE (168°) from Pingree Grove, IL
* 6 km (4 miles) SW (215°) from Gilberts, IL
* 9 km (6 miles) WSW (243°) from Sleepy Hollow, IL
* 34 km (21 miles) NNW (344°) from Aurora, IL
* 65 km (40 miles) WNW (292°) from Chicago, IL
Location Uncertainty horizontal +/- 7.3 km (4.5 miles); depth fixed by location program
Parameters NST= 16, Nph= 16, Dmin=179.1 km, Rmss=0.54 sec, Gp=104°,
M-type=regional moment magnitude (Mw), Version=8
Source
* USGS NEIC (WDCS-D)
Event ID us2010snay
