THE NEW MADRID FAULT SYSTEM EXTENDS 120 MILES SOUTHWARD from the area of Charleston, Missouri, and Cairo, Illinois, through New Madrid and Caruthersville, following Interstate 55 to Blytheville and on down to Marked Tree, Arkansas. It crosses five state lines and cuts across the Mississippi River in three places and the Ohio River in two places.
THE FAULT IS ACTIVE, AVERAGING MORE THAN 200 MEASURED EVENTS per YEAR (1.0 or more on the Richter scale), about 20 per month. Tremors large enough to be felt (2.5 – 3.0 on the Richter scale) are noted annually. Every 18 months the fault releases a shock of 4.0 or more, capable of local minor damage. The most recent registering 4.3 along the New Madrid Fault on Thanksgiving evening, 1996, which was felt by citizens in the states of Missouri, Arkansas, Tennessee and Kentucky, Illinois and Mississippi. Magnitudes of 5.0 or greater occurring about once per decade, can do significant damage, and be felt in several states.
THE HIGHEST EARTHQUAKE RISK in the UNITED STATES outside the West Coast is along the New Madrid Fault. Damaging tremors are not as frequent as in California, but when they occur, the destruction covers over more than 20 times the area because of underlying geology.
A DAMAGING EARTHQUAKE in this AREA, 6.0 or greater, occur about every 80 years (the last one in 1895). The results would cause serious damage to schools and masonry buildings from Memphis to St Louis.
A MAJOR EARTHQUAKE in this AREA, 7.5 or greater, happens every 200- 300 years (the last one in 1812). There is a 25% chance by 2040. A New Madrid Fault rupture this size would be felt throughout half the United States and damage 20 states or more. Missouri alone could anticipate losses of at least $6 billion from such an event.
THE GREAT NEW MADRID EARTHQUAKE OF 1811-1812 was actually a series of over 2000 shocks in five months, five of which were 8.0 or more in magnitude. Eighteen of these rang church bells on the Eastern seaboard. The very land itself was destroyed in the Missouri Bootheel, making it unfit even for farmers for many years. It was the largest burst of seismic energy east of the Rocky Mountains in the history of the United States and was several times larger than the San Francisco quake of 1906.
WHEN WILL ANOTHER EARTHQUAKE HAPPEN THE SIZE OF THOSE IN 1811-1812? Several lines of research suggest that the catastrophic upheavals like those in 1811-12 visit the New Madrid region every 500-600 years. Hence, emergency planners, engineers, and seismologists do not expect a repeat of the intensity of the 1811-12 series for at least 100 years or more. However, even though the chance is remote, experts assign a 3% probability of a major earthquake by the year 2040. Earthquake probabilities for known active faults always increase with time, because stresses within the earth slowly and inexorably mount, year by year, until the rocks can take no more, and sudden rupture becomes inevitable.
OUR GREATEST CONCERNS ARE THE 6.0-7.6 SIZED EVENTS, which do have significant probabilities in the near future. A 6.0 shock has a 90% chance by the year 2040. Damaging earthquakes of this magnitude are a virtual certainly within the lifetimes of our children.
WHAT is the RICHTER SCALE? The Richter Scale of earthquake magnitude is a measure of the energy released at the source of an earthquake deep within the earth. It is determined by measuring the amplitudes of ground motion on seismograms. An earthquake has a fixed amount of energy and only one Richter magnitude.
HOW MUCH INCREASE in ENERGY DOES EACH UNIT of the RICHTER SCALE REPRESENT? It is incorrect to say that each unit of the Richter scale corresponds to a tenfold increase in energy. Each unit, say from 5.2 to 6.2, actually represents 31.6 times difference in energy release. Every two units represent 1,000 times more energy, and every two-tenths of a unit represents double the energy.
IF a FAULT HAS LOTS of LITTLE EARTHQUAKES, WILL LARGER ONES BE PREVENTED? The answer is, “NO”. A magnitude 6.0 (which is damaging) is 1,000 times more energy than a 4.0 (which is not damaging). An 8.0 (which is devastating) is 1,000 times larger than a 6.0. In other words, a fault would have to have 1,000 4.0 events to prevent the occurrence of a single 6.0, or a million 4.0 events (1,000 times 1,000) to prevent a single 8.0.
Before an Earthquake strikes there are a few simple and inexpensive precautions you can take to lessen the potential damage but more importantly to lessen injuries. Know your environment, understand what has the potential for falling, rolling or swinging when an earthquake strikes.