THE KENTUCKY EARTHQUAKE PAGE
 
Where Kentucky Rocks - N - Rolls!
The New Madrid Seismic Zone
 
(Source: T. Mullins)
 
Where is the New Madrid Seismic Zone?
 
 
(source: University of Missouri)

   Located in the central Mississippi Valley, the northern end of the New Madrid seismic zone (NMSZ) is marked approximately by the confluence of the Ohio and Mississippi Rivers.  From this point in southern Illinois, the zone runs southwest, through western Kentucky (near Fulton), through eastern Missouri and western Tennessee to terminate in northeastern Arkansas.  Along this course, the NMSZ crosses the Mississippi River three times.
 

What is the New Madrid Seismic Zone?
 

    (source: Mooney, et al.)
    The NMSZ is a series of strike/slip and dip/slip faults associated with what is called the Reelfoot Rift (see above figure).  The Reelfoot Rift is a failed Precambrian mid continental rift, which is a fancy way of saying that a long, long time ago, the North American continent tried to split in two, but stopped before it succeeded.  This rifting resulted in the series of faults that make up the NMSZ.  The rift itself is about 70 km wide, and follows the same NE-SW path as the NMSZ.
    The continental crust that is faulted in this region is very old, thick, and brittle.  Much more so than the crust in California split by the San Andreas Fault.  What this means is that the seismic waves generated from an earthquake in the NMSZ will travel longer distances than those from an equivalent quake in California.  For example, the 1906 San Francisco earthquake (magnitude 7.8) was felt as far as central Nevada, 350 miles away.  The December 16, 1811 earthquake in New Madrid, MO (magnitude 8.0) rang church bells in Boston, MA, over 1000 miles away!
    Continuing the comparison with San Andreas, you may have seen some of the spectacular pictures of the San Andreas Fault cutting through the CA desert, but have you ever seen such pictures of the New Madrid?  No, not unless you've seen some seismic interpretations, because the New Madrid faults are buried beneath several thousand feet of alluvium (river deposits of sand, silt, and mud sediments).
 

Is there anything going on there today?

    Actually, the NMSZ is the most seismically active region in the United States east of the Rockies (see opening figure at the top of the page).  There are other active regions, however, including the Nemaha Ridge in Kansas and Nebraska and the Southern Appalachian Seismic Zone that extends into the eastern areas of Kentucky.  According to the Center for Earthquake Research and Information (CERI), there are approximately 200 earthquakes in the NMSZ every year, of which only 8 to 10 are large enough for us to feel (magnitude 3.0 and up).  Due to the activity of the NMSZ and the potential for tremendous damage in the event of a large quake (6.5 or more), large amounts of seismic detection equipment began to be installed in the fault zone in 1974.  Since then, these instruments have recorded over 4000 earthquakes!
 

So there's a lot of activity in the NMSZ.  Most of it's small, so what's the big deal?

    As previously mentioned, due to the high population density of the area in and around the NMSZ (Memphis, Little Rock, Birmingham, Nashville, St. Louis, Louisville, and Paducah are all within 250 miles of the most seismically active part of the NMSZ), if a big quake does hit, there's potential for great loss of life and massive property damage.  And on top of this... IT'S HAPPENED BEFORE.
    The winter of 1811-12 saw the largest earthquake in history strike the contiguous United States.  December 16, 1811 was the first of three great earthquakes to strike the New Madrid area.  The magnitude of this shock is estimated to be between 7.7-8.3, while the other two big ones, January 23 and February 7, 1812, weighed in at 7.6-8.3 and 7.9-8.8 magnitudes, respectively.  The epicenter of these earthquakes was near the town of New Madrid, MO (thus the name New Madrid Seismic Zone).  There were more than 2000 aftershocks for up to a year following the first quake, of which at least 12 were large enough to ring church bells on the eastern seaboard of the US.  During this time, it is thought that the entire 300 km of the fault shifted position.  All three of these earthquakes have made the United States Geological Survey's (USGS) top ten quakes to strike the contiguous U.S.: Feb. 7, 1812 is the largest, while Dec. 16, 1811 is #5 and Jan. 23, 1812 is #8.
    This series of earthquakes was felt across the entire central U.S., from the Rockies to the Atlantic coast, and at least as far north as Quebec: an estimated 2 million square miles!  According to eye-witness accounts, the ground cracked, fissured, and rolled in visible waves, trees topples, landslides occurred, and the Mississippi River reportedly reversed flow direction in some locations!  However, despite the violence of this seismic sequence, less than 100 people lost their lives.  This is because of the low population density in the region in the early 1800's.  For example, the town of New Madrid, MO had a grand total of 400 residents in 1811-12.  While this was responsible for the low loss of life and property damage, it also meant that news of the source and true magnitudes of the earthquakes, as well as some of the aftershocks, went unknown for a long time.  This was also due in part to the slow lines of communication with the larger cities to the east, as well as the low literacy rate of the region's populace.  For a more detailed description of the events of 1811-12, check out the Virtual Times, or our References section.
    The 1811-12 earthquakes haven't been the only significant seismic activity in the NMSZ.  An event on January 4, 1843 registered a 6.0 magnitude, while on October 31, 1895 a magnitude 6.2 quake struck.  Since 1812 there have also been 7 earthquakes measuring at least a magnitude 5.0.
 

Is there any way to tell if or when a major earthquake is going to hit the NMSZ?

    Based on the calculated recurrence intervals of different size (magnitude) earthquakes (i.e. how often a magnitude X.YZ earthquake occurs), seismologists have come up with a probability sequence for the NMSZ.  In a nutshell, the table below describes the recurrence intervals (in years) of different sized quakes, as well as the probability (percentage) that a given size event will occur within the next 15 (PROB15) and 50 (PROB50) years (starting from 1990).
 

Periodicity of Earthquakes for the NMSZ 
 Magnitude
 Recurrence
 PROB15
 PROB50
 >8.0
 550-1200
 0.3-1
2.7-4.0 
 7.0
 255-500
 5-9
 19-29
 6.0
 70-90
 40-63
 86-97
 5.0
 10-12
 ~100
 ~100
 4.0
 14 months
 ~100
 ~100
 
    From the above chart, it is apparent that there is a great chance that a magnitude 6 earthquake will strike before the year 2040.  What does this mean?  Well, we have already discussed the high population density of the area in and around the NMSZ.  This, coupled with the fact that nearly none of the structures in this area were built to withstand an earthquake ("In Kentucky?  Sure, if we lived in California, but not in Kentucky."), translates into the potential for massive amounts of property destruction and loss of life.  It has been estimated that if an earthquake similar to that of December 16, 1811 were to strike today, thousands of deaths would result, as well as billions of dollars in damage, including: fallen buildings (especially those constructed on unconsolidated, alluvial sediments); landslides; land subsidence (including sinkhole collapse!); and disruption of gas and electric utilities, and water and sewer services.
 

Are there any preparations being made in anticipation of something like this?

    Presently, Kentucky and the other states potentially affected by a large earthquake are taking several strides towards preparing for such an event.  In 1993, Kentucky, Tennessee, Missouri, Arkansas, Mississippi, Illinois, and  Indiana formed the Central United States Earthquake Consortium (CUSEC) in order to foster public awareness and education of earthquake dangers, as well as to garner further research within the NMSZ, and coordinate intra- and interstate response programs in the event of a large quake.
    Individually, the state of Kentucky has taken further preparatory steps.  For instance, the state legislature has mandated that "earthquake education" be taught in the public school system, the state has established an "Earthquake Awareness Week," and in 1990 the state Transportation Cabinet initiated a program to strengthen highway bridges that do not meet earthquake design standards.
    While there is still much to do in preparation for a large earthquake, especially in the areas of public awareness and education, we're moving in the right direction.


Where can I go to learn more about earthquakes and the New Madrid Seismic Zone? 

Books and Journal Papers

1) Bolt, Bruce A. 1993. Earthquakes.  W. H. Freeman and Co., New York; 331 pp. ISBN 0-7167-2236-4
 
2) Jibson, Randall W., and D.K. Keefer. 1988. Landslides triggered by earthquakes in the Central Mississippi Valley, Tennessee and Kentucky. USGS Professional Paper 1336-C.
 
3) Nuttli, Otto W. 1995. The Effects of Earthquakes in the Central United States. Original printing from CUSEC, 1987.  Reprinted by Gutenberg-Richter Publications, Marble Hill, MO; 50 pp. ISBN 0-934426-50-3
 
4) Penick, James L., Jr. 1981. The New Madrid Earthquakes. University of Missouri Press, Columbia and London; 170 pp. ISBN 0-8262-0344-2

5) The New Madrid Fault: Living in Earthquake Country.  Printed by the Disaster and Emergency Services Dept. of the Commonwealth of Kentucky.  For more information, write KY Division of Disaster and Emergency Services, Boone National Guard Center, Frankfort, KY 50601, or call 506-564-8628.

Web Sites

1) Earthquake Facts and Follies - Good, general information on quakes (causes, measurement, etc.).

2) The New Madrid Fault System - Good general introduction to the NMSZ.

3) Introduction to New Madrid - Short introduction and basic information.
 
4) The Mississippi Valley - "Whole Lotta Shakin' Goin' On" - General description of 1811-12 quakes with some pictures.
 
5) Cooperative New Madrid Seismic Network - Lists recent NMSZ quakes.
 
6) A Contribution to the Documentation of the 1811-1812 Mississippi Valley Earthquake Sequence - Scientific paper by R. Street (UK Dept. Geology).  "The purpose of this paper is to present a summary of the information obtained to date about the Mississippi river valley earthquake sequence of 1811-1812."
 
7) 1973 Paper on Magnitudes of 1811-12 Earthquakes - Published by Nuttli, who did a great deal of well-respected work on the NMSZ.  "The purpose of the present paper is to give some quantitative estimate of the magnitude and energy of the principal earthquakes of the 1811-1812 sequence."
 
8) University of Memphis info on NMSZ - Gopher menu.