1968 Illinois earthquake

1968 Illinois earthquake

Isoseismal map for the event (I–III are Not felt to Weak, IV is Light, V is Moderate, VI is Strong, VII is Very strong)
UTC time	1968-11-09 17:01:38
ISC event	814965
USGS-ANSS	ComCat
Local date	November 9, 1968 (1968-11-09)
Local time	11:01:40 CST
Magnitude	5.3 mb[1]
Depth	19 km (12 mi)[2]
Epicenter	37°57′N 88°29′W / 37.95°N 88.48°W / 37.95; -88.48[3]
Type	Dip-slip
Max. intensity	MMI VII (Very strong)
Casualties	None

The 1968 Illinois earthquake (a New Madrid event)^[4] was the largest recorded earthquake in the U.S. Midwestern state of Illinois. Striking at 11:02 a.m. on November 9, it measured 5.3 on the Richter scale.^[5] Although no fatalities occurred, the event caused considerable structural damage to buildings, including the toppling of chimneys and shaking in Chicago, the region's largest city. The earthquake was one of the most widely felt in U.S. history, largely affecting 23 states over an area of 580,000 sq mi (1,500,000 km²). In studying its cause, scientists discovered the Cottage Grove Fault in the Southern Illinois Basin.

Within the region, millions felt the rupture. Reactions to the earthquake varied; some people near the epicenter did not react to the shaking, while others panicked. A future earthquake in the region is extremely likely; in 2005, seismologists and geologists estimated a 90% chance of a magnitude 6–7 tremor before 2055, likely originating in the Wabash Valley seismic zone on the Illinois–Indiana border or the New Madrid fault zone.