Kentucky’s western 24 counties earthquake threat comes from three primary seismic zones:
The New Madrid Seismic Zone (NMSZ) is the U.S. region that scientists expect to be most vulnerable to a catastrophic earthquake. The NMSZ lies within the central Mississippi Valley, extending from northeast Arkansas, through southeast Missouri, western Tennessee and western Kentucky to southern Illinois. During a three month period during the winter of 1811 to 1812 there were a series of shocks that produced at least three quakes that were estimated to have a magnitude near, or greater than, 8.0. These quakes were felt throughout the U.S. and Canada. Hundreds of aftershocks followed over several months. Major quakes along the NMSZ occurred again in 1843 and 1895, the latter being a 6.8 that caused immense damage. Hundreds of quakes along this zone occur every year, although most are of a magnitude less than 2.0. Although the actual fault system does not extend directly into Kentucky, extreme physical destruction can be expected due to the underlying geologic and soil conditions that favor amplification of earthquake induced shaking and a bedrock system that lacks the necessary structure to attenuate earthquake energy.
According to the United States Geological Survey and the Center for Earthquake Research and Information at the University of Memphis, the following probabilities of an earthquake in the NMSZ over a 50 year period are as follows:
Probability of a repeat of the 1811 – 1812 earthquakes (magnitude 7.7 – 8.0) = 7 – 10%
Probability of a magnitude 6.0 or larger = 25 – 40%
The Wabash Valley Seismic Zone (WVSZ) is located in southeastern Illinois and southwestern Indiana. Scientists believe that it is capable of, and has produced, “New Madrid” size earthquake events. In the 1980’s, geologists found evidence of a prehistoric earthquake along the banks of the Wabash River with an estimated magnitude of 7.0. Current research is still turning out new evidence of earthquake activity in this zone. The WVSZ is still very active as proven by a 5.0 earthquake that occurred in the Evansville area on June 18, 2002; as well as most recently, the April 18, 2008 5.2 magnitude earthquake that was felt throughout much of Western Kentucky, southern Indiana and other Midwest states that was epicentered approximately 25 miles southwest of Vincennes, Indiana.
As a point of comparison to the 5.2 magnitude April 18, 2008 earthquake: a 6.2 quake would produce ten times the level of shaking with approximately 30 times as much energy released; a 7.2 magnitude event would produce 100 times the level of shaking with nearly 1,000 times as much energy released.
The Rough Creek Fault System (RCFS) extends approximately 100 miles across western Kentucky. This fault crosses the Ohio River into Illinois where it is known as the Shawneetown Fault Zone. Three different types of faulting and recurring movement are evident, and together they interact to form an extremely complex fault pattern. Faulting in this system probably began with wrench faulting in Precambrian time. Subsequent faulting included both normal and reverse movement, which produced primarily high-angle to vertical faults. Evidence does not support significant strike-slip movement at the surface, or in the shallow subsurface.
Earthquake damage from activity in the NMSZ, the WVSZ or the RCFS is expected to be the most significant in the northwestern part of Kentucky, including Henderson County, with damage decreasing incrementally throughout the remainder of the state. However, the direct damage, as well as the effects on our basic infrastructure support services (communications, electric, natural gas, etc.) could be of a catastrophic nature throughout a large portion of the state.
Earthquakes are no-notice events that occur without warning, thereby increasing the likelihood of casualties and damage to property.
Because of the growth and dispersal of the population and the accompanying development of critical infrastructure that is required to sustain this population, any significant earthquake event, especially over a 6.0 magnitude, could cause catastrophic impacts within Henderson County, as well as a large portion of Kentucky and other states.
Although the greatest hazard potential is in highly populated areas, the majority of Kentucky is a more sparsely populated area.
The University of Kentucky currently operates a network consisting of 10 seismic stations and eight strong-motion stations. The seismic network is capable of monitoring any earthquake occurring in Kentucky with a magnitude larger than 2.0, as well as major earthquakes in the central United States. The strong-motion network is designed to record strong ground motions that have engineering significance in the New Madrid Seismic Zone. The nearest monitor is located in Union County.
Below are a few resources to help you prepare: