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. You can see real-time recordings from the Kentucky Seismic Network here.
Information on earthquakes occuring in the central United States and other areas are available from the Center for Earthquake Research and Information at the University of Memphis, and from the U.S. Geological Survey.
Kentucky is affected by earthquakes from several seismic zones in and around the state. The most important one is the New Madrid Seismic Zone, in which at least three great earthquakes, each estimated to have been greater than magnitude 8 on the Richter scale, occurred from December 1811 to February 1812. Though the state was sparsely settled, these great earthquakes affected the whole Commonwealth of Kentucky. The following quotes are taken from newspaper articles published after the December 16, 1811, quake.
Frankfort. "About two o'clock on Sunday night was felt in this place a violent shock of an earthquake. It continued for several minutes and produced a considerable vibration of houses. Some bricks are said to have fell from the top of the court house chimney" (The American Republic, Frankfort, Ky.).
Henderson. "A severe shock of an earthquake was felt at this place on the 16th inst. At half past 2 o'clock, A.M. -- many chimneys were cracked by the motion; -- and at sun-rise another shock threw down most of the chimneys so injured" (The Weekly Register-Chronicle, Washington, D.C.).
Lexington. "About half after two o'clock, yesterday morning, a severe shock of an earthquake was felt at this place: the earth vibrated two or three times in a second, which continued for several minutes, and so great was the shaking that the windows were agitated equal to what they would have been in a hard gust of wind" (Kentucky Gazette, Lexington, Ky.).
Louisville. "On Monday morning the 16th instant, this place was visited by a most alarming Earthquake. . . . We are induced to believe, the continuation was from 4 to 6 minutes, though some say it was not so long; -- about an hour afterwards, another shock was felt; and a little after sunrise, a third, which broke off several chimneys, and injured some houses otherwise" (Poulson's American Daily Advertiser, Philadelphia, Pa.).
The map below shows the Modified Mercalli intensity for the first event of the 1811-1812 New Madrid earthquakes.
An earthquake measuring 5.2 on the Richter scale occurred in 1980 near Sharpsburg in Bath County and caused an estimated $3 million in damage; 269 homes and 37 businesses in nearby Maysville were damaged. Thus, earthquakes pose high seismic hazards and risk to the Commonwealth of Kentucky. A preliminary estimate by the Federal Emergency Management Agency (FEMA) of annual earthquake loss in Kentucky is about $18.7 million.
How earthquakes affect humans, buildings, and bridges depends on many factors. The most important factors are earthquake magnitude, the distance from the earthquake center (called the epicenter), and the geologic conditions at a site.
Most damage during an earthquake is caused by ground
motion. This photo shows the total collapse of the Juarez Hospital in Mexico
City, caused by strong ground motion during the earthquake of September 19,
1985. The larger an earthquake's magnitude, the stronger the ground motion it
generates. The level of ground motion at a site depends on its distance from
the epicenter -- the closer a site is to the epicenter, the stronger the ground
motion, and vice versa. Ground motion from a major earthquake in the New Madrid
Seismic Zone is expected to be much stronger in western Kentucky than in the
central and eastern parts of the state.
The local geology and soil also play very important roles in earthquake damage. Soft soils overlying hard bedrock tend to amplify the ground motions -- this is known as ground-motion amplification. Amplified ground motion can cause excess damage, even to sites very far from the epicenter. Ground-motion amplification contributed to the heavy damages in Mexico City during the 1985 Mexico earthquake and in the Marina district of San Francisco during the 1989 Loma Prieta earthquake; both areas were more than 100 km away from the epicenters. Most of the damage in Maysville during the Sharpsburg earthquake of July 27, 1980, was caused by ground-motion amplification.
Soft sandy soils can be liquefied
by strong ground motion -- a process called liquefaction. Liquefaction
can result in foundation failure. The photo at left shows that
sandy soil was liquefied and behaved like fluid during the Nisqually,
Washington, earthquake of February 28, 2001.
Many communities in Kentucky are
set on soft soils, especially those along the Ohio and Mississippi
River Valleys. Those communities are prone to ground-motion amplification
and liquefaction hazards. The strong ground motion can also trigger
landslides -- known as earthquake-induced landslides --
in areas with steep slope, such as eastern Kentucky. This slope
failure was caused by the Nisqually, Washington, earthquake of
February 28, 2001.
Although we do not know when and where the next major earthquake will occur, we do know that an earthquake will cause damage, and the damage depends on many factors, such as earthquake magnitude, the distance from the epicenter, and local geology. Information on earthquake effects can be obtained by monitoring earthquakes and performing research. Such information is vital for earthquake hazard mitigation and risk reduction.
The most important information for seismic-hazard mitigation and risk reduction is ground-motion hazard. One way of predicting ground-motion hazard is by determining the peak ground acceleration (PGA) probably occurring in a particular timeframe. The map below shows the PGA at the top of bedrock that will probably occur in the next 500 years in Kentucky (Street and others, 1996). It shows, as expected, that PGA would be greatest in far western Kentucky near the New Madrid Seismic Zone. Ground-motion hazard maps for the central United States and other areas are available from the U.S. Geological Survey. These maps are used to set general policies on mitigating damage. For example, maps produced by the USGS in 1996 were used to determine seismic design in building codes.
Seismic hazards associated with local geology,
such as ground-motion amplification, liquefaction, and slope failure, also need
to be considered in seismic-hazard mitigation and risk reduction. The map at
right shows ground-motion amplification potential for the Jackson Purchase Region
of western Kentucky (compiled by Street and others, 1997). The shaded areas
represent classification C, very dense soil and soft rock, which means a low
potential for ground-motion amplification. Mitigation measures in local communities
can be fine-tuned by considering how the local geology relates to the hazard
potential.
For information on the seismic network and seismic hazards, please contact the Department of Geological Sciences at 859.257.3758 or the Kentucky Geological Survey at 859.257.5500, both at the University of Kentucky. The Kentucky Division of Emergency Management and FEMA Web sites have information on earthquake preparedness.
Bolt, B.A., 1993, Earthquakes: New York, W.H. Freeman and Company.
Street, R., Wang, Z., Harik, I., and Allen, D., 1996, Source zones, recurrence rates, and time histories for earthquakes affecting Kentucky: Kentucky Transportation Center, University of Kentucky, KCT-96-4.
Street, R., Woolery, E., Wang, Z., and Harik, I.E., 1997, Soil classifications for estimating site-dependent response spectra and seismic coefficients for building code provisions in western Kentucky: Engineering Geology, v. 46, p. 331-347.