New Madrid Fault: Earthquakes in Kentucky

Just when we think life is under control, Mother Nature surprises us with something new or unusual.

Emerging issues such as methicillin-resistant Staphylococcus aureus infections in horses, ivermectin-resistant parasites, and the ever-present threat of foreign animal disease pathogens entering the United States via insects or migrating birds pose never-ending challenges to researchers, in both veterinary and human medicine.

After first being recognized in the 1960s, equine neurologic herpesvirus disease was diagnosed sporadically. It did not occur as recognized outbreaks of disease, as has been experienced recently. A mere one-point mutation in the DNA of the virus changes it from a "typical" herpesvirus respiratory or abortion clinical presentation to one that neurologically affects healthy adult horses. While it is an amazing feat of scientific discovery to have determined this mutation, researchers have significant work ahead in seeking effective prevention and treatment for this devastating disease.

Natural surprises can also appear in the forms of deeply buried faults in the earth's geography, such as the New Madrid Fault. It is likely not known by a majority of veterinarians and equine owners that this fault is in the middle of the American heartland along the central Mississippi River Valley from northeastern Arkansas to southern Illinois. Because of the difference in geography between California and the Mississippi River Valley, an earthquake at the New Madrid Fault of 6.0+ on the Richter Scale would be much more devastating than in California.

Why are earthquakes discussed in this issue of the Equine Disease Quarterly? Imagine that all bridges crossing the Mississippi River from St. Louis to Memphis were so structurally damaged that they were closed for weeks to months, even years. The impact on commerce, travel, and infrastructure would be enormous, including that to horse farms and all ancillary businesses. A major New Madrid Fault earthquake could impact a significant portion of the United States, making the hurricanes of 2005 seem like a warm-up exercise in disaster management. Preparation for unexpected events as well as predicted blizzards, tornadoes, flooding, etc., is critical to the horse economy.

While this discussion may sound like the plot of a made-for-TV movie, the reality is that the New Madrid Fault is real, and earthquakes cannot be predicted like some other major natural disasters. Preparing for common natural disasters can go a long way toward preparing for a rare, but significant, disaster, whether it be an earthquake, an overturned tanker or railway car carrying hazardous materials, or a barn fire.

Likewise, having a biosecurity plan in place for that unexpected disease outbreak of fetal losses, respiratory or diarrheic disease or, in the worst case, diseases of undetermined etiology and transmission, can make response time much faster and less costly than having to plan and implement at the same time.

Preparing for the worst with an emergency family and animal plan can make the anticipated, predictable disasters more manageable. Mother Nature almost always has the last word.

Contact: Dr. Roberta M. Dwyer, 859/257-4757,, Maxwell H. Gluck Equine Research Center, University of Kentucky, Lexington, Kentucky.

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

Earthquakes are the most devastating of natural hazards and not usually considered as a potential risk to property or lives in the southeastern United States. The West Coast of the United States is under constant threat of a large earthquake and experiences smaller seismic events on a daily basis (see map). Less recognized is the considerable seismic activity in the Kentucky area. A series of earthquakes with the most extensive impact ever recorded occurred 200 years ago just west of Kentucky along the New Madrid Fault zone. This area, comprising 220 miles of major faults, stretches from New Madrid, Missouri, far south of Blytheville, Arkansas, and consists of seven major connecting faults.

Earthquake Map

From December 1811 to March 1812, an estimated 3,600 shocks were generated in the New Madrid Fault zone, including three major quakes thought to have been of a magnitude of 8.1 or greater on the Richter scale. The area with most severe damage covered 5,000 square miles, and the effect on the landscape and settlers in the region was profound. Eyewitness accounts of these events describe the land as "undulating like the ocean," the disappearance of hundreds of miles of riverbank along the Mississippi, and the creation of 10 large lakes. Chasms opened in the ground, acres of land were thrust up in the air, and entire towns and villages were lost in each of the large quakes. Tremors were severe throughout Kentucky, with buildings impacted by shaking as far away as Montreal. Church bells rang in Pennsylvania and South Carolina as a result of the quakes. Significant damage to people, animals, and property was felt in an area the size of Texas, but the shaking was experienced over an area of 1 million square miles.

Earthquakes, like volcanoes, are usually associated with active plate boundaries where two large tectonic plates collide, such as the subduction zone around the Pacific Ocean. The infamous San Andreas Fault, which has produced several large earthquakes in the past 200 years, is part of a major boundary between the North American and Pacific plates, which move laterally relative to each other in California at a rate of about 1 inch per year.

It is less clear, however, how a huge earthquake could have been triggered within a stable plate, such as the New Madrid Fault, rather than at the volatile boundaries, such as at the San Andreas Fault. The question remains: can such a large quake occur again on the New Madrid Fault? If so, when?

The New Madrid Fault zone is somewhat of an enigma, which makes estimating the likelihood of future earthquakes very difficult. Palaeoseismic studies in this area have deduced that large earthquakes did occur previously, with four major events in the last 1,500 years. Typically, these large quakes occur in "triplets," or temporal clusters, as they did in 1812. On the other hand, there is no surface evidence of movement of the earth's crust along these faults, which would suggest limited buildup of stress to trigger another earthquake. Geologists have hypothesized that magma intrusions at depth facilitate these large earthquakes like a volcanic eruption that does not break the surface and that the vast extent of destruction is a result of the deep ocean and river sediments in the Mississippi embayment, which are readily deformed and transmit stress much farther than bedrock.

Presently, seismic activity is monitored in the New Madrid Fault zone, and earthquakes occur on a weekly basis. Most of these register below 2.0 on the Richter scale, but occasionally larger quakes are recorded, such as the 4.0 event near Paducah in 2003. When will the next "big one" hit in this area? No one knows.

Contact: Dr. Alice V. Turkington, 859/257-9682,, Department of Geography, University of Kentucky, Lexington, Kentucky.

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Equine Disease Quarterly

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