The New Madrid Earthquakes from 1811-1812 did cause physical damage, but also changed the topography of the Mississippi River Valley and surrounding areas. The exact magnitude of the earthquakes, damage and death totals, and precise details are unknown. However, an accepted value is that the five largest earthquakes, which happened between December 16, 1811, and February 7, 1812, were over magnitude 7.0. Researchers believe that there were two earthquakes in Arkansas, two in Missouri, and one in Mississippi. These earthquakes did not cause much damage or death in 1812, but if earthquakes of this magnitude occurred now, the damage would be catastrophic. As such, it is important to know if something of that magnitude is even possible in the current landscape. It is also critical to analyze the measures being taken in major cities along the New Madrid fault to guard against earthquake damage in the future. The image below from the U.S. Geological Survey shows earthquake activity along and around the New Madrid fault.
Because this disaster happened over 200 years ago, records of the event are limited, and accuracy cannot be proven. In addition, because this event occurred at a time in history when cities were less populated and there were less cities in this area overall, the reports of damage and death are minimal. Reports indicate that between December 1811 and March 1812, there were over 2000 earthquakes and aftershocks along the New Madrid fault. The largest earthquakes were over magnitude 7.0, with some reports suggesting they were over magnitude 8.0. The largest quake occurred on February 7, 1812, with majority consensus indicating it was most likely a magnitude 7.5 earthquake. Because of the limited quantity of major cities and population centers along the New Madrid fault at this time, the majority of the damage is seen in the landscape. Eyewitness reports indicate that the ground rose and fell like waves, eventually creating deep cracks in the earth. As a result, some areas of ground were lifted up while some others sank deeper. Many people were reported missing after the earthquakes and were assumed to have fallen into these cracks, some of which were as long as five miles. Most of these areas that sank were eventually filled with water and became lakes or new streams; this is how Reelfoot Lake came to exist as a result of a dip-slip fault. Because of all this movement of the earth, mudslides and landslides were numerous especially on the bluffs and steeper hillsides around the Mississippi River.
There were eyewitness reports from people boating on the Mississippi River that the river flowed backward for several hours after one of the largest earthquakes that occurred on December 16. Scientists have since determined that this optical illusion was likely due to the large waves in the river and local, small-scale uplifts and sinking of the riverbed. This would push the water in a different direction than it typically flows. These large waves were also reported to have flooded several boats and washed many others high on to the shore. People also reported sandbars and small islands disappearing due to the high waves and restructuring of the riverbed from the earthquake. The earthquake caused bluffs, hillsides, and coastline to collapse into the river in many places. One of the largest lasting impacts from this event is the curve in the Mississippi River through New Madrid, Missouri. Due to a strike-slip fault, the river flows to the north around a tight bend that channels it through New Madrid and back down its original path. The Google satellite image below shows the Mississippi River through New Madrid outlined in blue, with that tight bend to the north circled in red. The red arrow shows something closer to the original path of the river.
Another reason the damage cost was so minimal, besides the sparsely populated landscape, is due to the type of home construction from the time period. Most homes in this part of the country were log cabins that handled the shaking well. In the bigger cities, there were more chimneys that fell, causing more damage. The majority of the damage reported occurred in cities along the Mississippi River and New Madrid fault, but people as far away as Washington D.C., New York City, Boston, and Montreal reported feeling the earth shake and hearing church bells ring. People also reported animals behaving strangely before the earthquakes. Domestic animals acted wild while wild animals acted more tame. Snakes came out of the ground and flocks of birds landed near people. These behavioral traits have been documented before more recent earthquakes as well, so they can be an indicator that something is coming. The map below from the U.S. Geological Survey shows how far away shaking was felt from the earthquake on December. 16, 1811.
Memphis is in an area that was affected by the 1811/1812 New Madrid earthquakes, but the city was not nearly as large then as it is now. The City of Memphis Office of Emergency Management councils residents to “Drop, cover, and hold on” during an earthquake and to have an Earthquake Supplies Kit ready. They also provide advice on their website of what to do before, during, and after an earthquake. Because that area has gone so long without experiencing a large magnitude earthquake, residents have become complacent about the threat. Scientists and experts suggest that because there is minor and moderate seismic activity continuing in the Mississippi River Valley region, an earthquake of larger magnitude, comparable to the 1811/1812 event, can be expected. Archaeological and geologic studies suggest that large earthquakes around magnitude 7 occur in the New Madrid zone about every 500 years, though some scientists suggest it could be as little as every 200 years. If a large magnitude earthquake like this occurred in the near future, there would be a much greater loss of life and property. This is obviously due to the increase in population and man-made structures in the region. More than 200 years after the 1811/1812 New Madrid earthquakes, a conference of 500 international experts met to discuss the lasting impacts of this event. At this conference, experts presented research that estimated a magnitude 6.4 to 6.9 earthquake near Memphis could cause up to $130 billion in property damage, while losses from a 7.7 magnitude event could be greater than $250 billion.
The U.S. Geological Survey map above shows the new Madrid seismic zone. The New Madrid Seismic Zone (NMSZ) Catastrophic Planning Project began in 2006 as the largest multi-state response-planning project. It involves first-responders, geologists and other decision makers from local, state, and federal levels in the planning process. Though this group prepares for other kinds of disasters, they have extensive planning and research dedicated to earthquakes in the New Madrid Zone. This project involves officials from Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and Tennessee as these are the states that would be most affected by a catastrophic earthquake. They operate on a scenario-based planning process, which was unique to this group when it began. This allows them to use past events as well as imagined scenarios to prepare for future disasters. NMSZ is not the only group of it’s kind; many states have their own disaster preparedness program for earthquakes.
The image above from the U.S. Department of Agriculture shows an example of how the topography has been permanently changed near Lepanto, Arkansas. The city of Memphis and the U.S. Government are trying to educate the public about the risks and dangers associated with earthquakes. Buildings must be built in compliance with regulations that will allow them to stand up against low to moderate earthquakes, though specific building codes vary between locations. These regulations are based on the specific location’s probability of earthquakes and the projected strengthening of earthquakes in the area. Buildings in Memphis are built to withstand even stronger earthquakes than average due to their location along the New Madrid fault zone. Unfortunately, it costs extra to make a building able to withstand magnitude 7, 8, and 9 earthquakes. Additionally, because of its location on a bluff near the Mississippi River, Memphis is at an extra risk of damage during an earthquake. The bluff has been built up from the sediment deposited there by the river, but sediment will not be stable ground in an earthquake because it is not compacted enough.