MEMPHIS, Tenn. (WMC) - The Mid-South is located along the New Madrid Fault which extends around 120 miles southward from Charleston, Missouri, through Mew Madrid and Caruthersville and follows I-55 to Blytheville, then to Marked Tree, Arkansas.
The New Madrid Fault crosses five state lines and intersects the Mississippi River in three places and the Ohio River in two places.
The fault system in the New Madrid Zone is not fully understood and earthquake predictions can pose unique challenges. In the central U.S., fault features are not expressed at the surface. They are covered by 100-200 feet of soil.
This differs from the West Coast where major earthquake activity is more understood and predictable. The predictions on the West Coast are based on measured movement at tectonic plate boundaries, whereas the New Madrid Fault is located near the center of the North American Plate which can make it harder to understand and predict.
Another difference is due to the terrain. In the central U.S. the harder, colder, drier, less fractured crust produces more shaking over larger areas than quakes of comparable magnitude on the west coast. Damage is even different from quakes in the central U.S. producing more damaged areas, around 20 times larger than similar West Coast quakes.
Earthquakes are unpredictable. The likelihood or probability can be calculated from patterns based on the past. Scientists can estimate that the average interval between magnitude 7.0 quakes or greater is approximately 500 years.
So far the earthquakes of 1811-1812 remain one of the largest quakes in history. During the 1811-1812 quakes, there were two major quakes that struck, on Jan. 23 and Feb. 7.
Each New Madrid earthquake had a magnitude of 7.5 or greater, making them some of the strongest in the continental United States and the quakes shook an area 10 times larger than that affected by the magnitude 7.8 San Francisco earthquake of 1906. The Mississippi rose so high that a portion of the river ran backward.
The USGS estimates that the risk for an earthquake of magnitude 7.5 to 8.0, the probability for occurrence is approximately 7-10 percent over the next 50 years. For a quake of 6.0 to 7.0, the probability is 28-46 percent over the next 50 years.