The New Madrid fault zone continues to be active and remains a threat to the Midwest United States. Although some scientists have declared the fault "dead," it continues to produce around 200 quakes each year. The New Madrid Seismic Zone includes several faults that run under the Mississippi River and through seven states.
Unlike faults that run along the West Coast, the intercontinental faults are located up to 200 feet below the surface. The depth makes them difficult to study as they cannot be visually observed. The zone's activity is constantly monitored by seismograph stations placed throughout the region. Although a majority of the tremors are not recognized by humans, the stations have detected an average of 200 quakes per year.
As reported by the Missouri Department of Natural Resources, most of the quakes in the New Madrid Seismic Zone are microseismic with a magnitude below 2.0. Over the last 200 years, the quakes have been quite small. However, between December 1811 and March 1812, three significant quakes were recorded along the New Madrid Fault Zone.
In the three-month period, seismologists recorded 15 quakes ranging from magnitude 6.5 to 8.0. Although a majority of the region was unpopulated, the tremors were recorded in numerous states.
The quakes destroyed the towns of New Madrid and Little Prairie, Missouri. An area of approximately 5,500 square miles was visibly damaged by landslides, fissures, submergence, and uplift. Much of the land remained unstable for years, reducing agricultural opportunities.
Some scientists suggest microseismic activity, recorded after the large quakes, is the result of aftershocks. However, new research suggests otherwise. The Weather Channel reports Geophysicist Morgan Page believes stress is building along the fault and may threaten the Midwest.
"200 years is too long for an aftershock sequence. Instead, we think stress is being built up now... The frequency of aftershocks... decreases with time, known in seismology as Omori's Law... in the New Madrid Seismic Zone, the aftershocks aren't following Omori's Law."
If the seismic activity is in fact new, and unrelated to aftershocks, the United States Geological Study suggests a 7 to 10 percent chance of a destructive quake within the next 50 years. As the New Madrid fault zone runs through Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and Tennessee, a large earthquake could be catastrophic.
Seismologist Arthur Frankel did not participate in the study. However, he agrees with the findings. Frakel said his own studies, using GPS, indicate " significant movement of land along the fault in the past decade."
A significant earthquake along the New Madrid fault zone is not likely imminent. However, it will be interesting to see if the seismic activity continues to increase.