New Madrid Seismic Zone

The Earthquakes of 1811-12

400 terrified residents in the town of New Madrid, Missouri were abruptly awakened by violent shaking and a tremendous roar. It was December 16, 1811, and it was the first of at least three very large (M7 or greater) earthquakes and thousands of aftershocks to rock the region that winter, with the last occurring on February 7, 1812.

Survivors reported that the earthquakes caused cracks to open in the earth’s surface, the ground to roll in visible waves, and large areas of land to sink or rise. The crew of the New Orleans (the first steamboat on the Mississippi, which was on her maiden voyage) reported mooring to an island only to awake in the morning and find that the island had disappeared below the waters of the Mississippi River. Damage was reported as far away as Charleston, South Carolina, and Washington, D.C.

The New Madrid Seismic Zone

These dramatic accounts clearly show that destructive earthquakes do not happen only in the western United States. In the past 25 years, scientists have learned that strong earthquakes in the central Mississippi Valley are not freak events but have occurred repeatedly in the geologic past. The area of major earthquake activity also has frequent minor shocks and is known as the New Madrid Seismic Zone. The NMSZ is made up of several thrust faults that stretch from Marked Tree, Arkansas to Cairo, Illinois.

Earthquakes in the central or eastern United States effect much larger areas than earthquakes of similar magnitude in the western United States. For example, the San Francisco, California, earthquake of 1906 (M7.8) was felt 350 miles away in the middle of Nevada, whereas the New Madrid earthquakes of 1811-12 were felt as far away as Connecticut – more than 1,000 miles away. Differences in geology east and west of the Rocky Mountains cause this strong contrast.

Potential Dangers

Map showing estimated shaking from a 7.7M on the NMSZ

This map from the US Geological Survey shows estimated levels of shaking from a hypothetical M7.7 earthquake along the southwestern portion of the New Madrid Seismic Zone.

The loss of life and destruction in recent earthquakes of only moderate magnitude (for example, 33 lives and $20 billion in the 1994 magnitude-6.7 Northridge, California earthquake and 5,500 lives and $100 billion in the 1995 magnitude-6.9 Kobe, Japan earthquake) dramatically emphasize the need for residents of the New Madrid Seismic Zone to prepare further for an earthquake of such magnitude. Earthquakes of moderate magnitude occur much more frequently than powerful earthquakes of magnitude 7 to 8, and the probability of a moderate earthquake occurring in the New Madrid Seismic Zone in the near future is high.

Scientists estimate that the probability of a magnitude 6.0 or larger earthquake occurring in this seismic zone within any 50 year period is 25% to 40%. Such an earthquake could hit the Mississippi Valley at any time.

In 1811, the central Mississippi Valley was sparsely populated. Today, the region is home to millions of people, including those in the cities of St. Louis, Missouri, and Memphis, Tennessee. Adding to the danger, most structures in the region were not built to withstand earthquake shaking, as they have been in more seismically active areas like California. Moreover, most earthquake preparations also have lagged far behind.

Recognizing these problems, CUSEC, our Member and Associate States, the Federal Emergency Management Agency (FEMA), U.S. Geological Survey (USGS) and other organizations are joining together to take actions that will greatly reduce loss of life and property in future temblors.