The New Madrid fault line is well recognized for causing some of the most severe earthquakes to ever strike the United States: four in 1811 and 1812. At that time, much of southern Missouri was covered by an extensive forest reserve called Jefferson Prairie. When the first two earthquakes hit, this forest was completely destroyed. Trees were toppled for hundreds of miles in all directions.
After the second earthquake, people began to build houses on top of the unstable soil. Within a few years, nearly every house in the area had been destroyed. Today, no buildings stand on this lost land except for some ruins of those who dared to build here before being forced out of their homes.
In addition to the buildings destroyed, many other things can be damaged by earthquakes: roads collapse, bridges are destroyed, water wells are polluted, and even small towns can be completely destroyed. After an earthquake, it can take years for the ground to become stable again and more damage may be done by subsequent earthquakes.
Scientists have learned a lot about how frequently these huge earthquakes occur along the New Madrid fault line and how severely they can damage buildings and other infrastructure. In fact, scientists now know that another large earthquake is likely to hit the New Madrid region within 100 years.
The most extensively felt earthquakes in North America's documented history were a sequence that occurred in 1811–1812 at New Madrid, Missouri. The largest known quake of this series was estimated to have had a magnitude of 7.6. It killed about 300 people and caused widespread damage and loss of property.
An aftershock of similar size struck three months later. These events are now considered manifestations of a large seismic zone of weakness within which small shocks can re-activate previously activated regions of the Earth's crust. New Madrid is not likely to experience another major earthquake for several centuries.
New Madrid is not the only place in America where large earthquakes occur regularly. California's San Andreas Fault produces many small earthquakes each year. In 2004, the strongest to date, a magnitude 6.0 shock occurred near the northern end of the fault. No deaths or serious injuries resulted from this event but it did cause considerable damage across much of Northern California.
Another big one is coming! The huge earthquake that destroyed large parts of Lisbon in 1755 has been identified as an example of a megathrust earthquake. These involve the sudden movement along a large portion of a continent-size plate boundary, like the Rio Grande Rift in South America or the Pacific Ocean's Juan de Fuca Plate.
Fault of New Madrid In the United States, a large earthquake in the late 1800s destroyed buildings in Charleston, SC; the Eastern Tennessee Seismic Zone experiences at least a thousand small earthquakes each year; and the largest earthquake in the continental United States occurred in the early 1800s along the New Madrid fault near St. Louis, Missouri.
Faults similar to the New Madrid one occur throughout the world, particularly in Europe where the Alps and other mountainous regions feature prominently on the global seismograph. The New Madrid fault runs for about 100 miles (160 kilometers) through southern Ohio and northern Kentucky from north of Louisville down to Cape Girardeau, Missouri. It extends even further under the city itself.
The New Madrid fault has caused significant damage over time with many large earthquakes occurring along it. In 1812-1814 more than 200 km3 (70 cubic miles) of land was deformed in huge slabs that were later found several hundred meters away from their original location. In 1957-58 another big quake hit the region with a magnitude of 6.5. Scientists now know this event was triggered by the first New Madrid earthquake because the two events are separated only by years—not decades or centuries like most other earthquakes.
In total, the New Madrid fault has caused significant damage every 150 years or so. Although it is still active today, its next major rupture will be long after we're gone.