New Madrid Earthquakes
The New Madrid seismic region in the central Mississippi Valley hides one of the greatest earthquake danger in the central United States. Four earthquakes of around magnitude 8 occurred in this seismic area in the winter of 1811-12, and this region continues to exhibit the highest level of seismicity in the central and eastern states of the Nation.
The early known history of large earthquake activity in the New Madrid seismic zone is documented by the earthquake swarm that struck the area in the winter of 1811-12. The sequence began on Dec. 16, 1811, with a unbelievable tremendous earthquake, followed by another very large aftershock about 6 hours later. Subsequent great earthquakes hit on Jan. 23 and February 7, 1812. In terms of historic magnitude, these rare earthquakes are believed to be the largest powerful shocks known to have taken place in a so-called stable continental interior; in terms of land area affected, they may be the strongest historical earthquakes felt in the world. In contrast to the typical pattern of a single earthquake shock that is followed by a set of aftershocks, the 1811-12 sequence was built on four huge shocks, each of which was followed by many swarm aftershocks, many of which were themselves very large earthquakes. Six of the aftershocks that struck had magnitudes of over a 6 to 7, and more than 1,800+ aftershocks big enough to be felt and recorded as far away as Louisville, Ky., hit in the first 5 months following the December 16, 1811, huge event. The aftershocks continued until at least well into 1817. About as many felt the earthquakes that occurred in the Mississippi Valley in 5 months, as occurred in southern California in the 40-year period from the 1933 Long Beach quake through 1971 Slymar quake. The most dangerous and intense earthquake activity in the Eastern United States continues to be in the shy New Madrid seismic zone.
New Madrid, Missouri, was the biggest settlement in the region at the time of the quakes, and the surrounding land were devastated in 1811-12. The New Madrid region continues to have the highest level of seismicity activity in the United States east of the Rockies. Earthquakes of estimated magnitude 6.3+ and 6.8+ occurred in the coming years of 1843 and 1895, respectively; statistical study indicate that earthquakes of magnitude greater than 6+ are expected at least once per each century. The 1900s was very quit, so the region is overdue and the crust has built up with many many years of back pressure.
The potential losses from any new earthquakes of magnitude 6 or larger in the New Madrid region are expected to be very, very large because of
(1) the high population growth over the last hundred years (Memphis, St. Louis, and many other growing towns).
(2) the large number of built non-seismic safe structures and industrial and transport features like airports, river bridges, and freeway overpasses, which generally were not reinforced to withstand HUGE earthquakes.
(3) the great thickness and area of poorly consolidated sedimentary rocks, which greatly amplify ground vibrations and S and P wave travel over huge areas.
(4) the very large region that would be inflicted by long lasting damaging ground motion (about 10 times bigger than the area affected by a California earthquake of comparable size). A future great earthquake (magnitude 8.0 or larger) has the possibility to cause huge damages in the hundreds of billions of dollars and deaths in the thousands unless cities and towns reduce their vulnerability through better preparedness and increased mitigation actions. Just a magnitude 6.5 earthquake could cause about $3.8 billion in losses to this areas housing. Currently this region needs to do way more and should be the first area to get federal infrastructure money when congress finally wakes up and stops playing politics with peoples lives.
Loss of life and damage from large earthquakes can be cut down through a variety of measures, all of which could be put into effect in the New Madrid region. The most relevant actions include:
☻ Improving current area building construction requirements and structure practices through better building codes and local regulations.
☻ Reducing building vulnerability by strengthening or knocking down hazardous tall brick and masonry buildings, particularly unreinforced(no rebar) masonry buildings, and strengthening foundations with better footings and connected shear walls. This important action should begin RIGHT NOW with the regions important hospitals, schools, and needed emergency centers. One of the important things to remember is reinforcing a building for tornados is TOTAL different than reinforcement for earthquakes. One deals with weather and wind and the other with the earth’s crust and geology.
☻ Increasing awareness and utilization of quake mitigation measures through public classes and education and yearly training of those who would be responsible to carry out the measures.
☻ Improving local public response times to earthquake disasters through increased preparedness planning involving realistic acted out scenarios of destructive earthquakes and the casualties.
Because such information is currently still incomplete for the New Madrid area, some of the major goals of an intensified research should be to improve the information that would be used as the basis for effect and mitigation.
An intensified study of the New Madrid seismic zone should focus on these five important goals:
1. Implementing earthquake-hazard mitigation measures for the region that is most likely to be hit.
2. Improving area preparedness for earthquakes of magnitude 6+ or greater.
3. Establishing a modern seismic warning/study network in the New Madrid seismic zone to monitor the locations, sizes, and characteristics of any earthquake(s) and to determine the nature of the ground movement that they produce.
4. Locating the many hidden faults that could generate huge earthquakes, determining the repeat rates of quakes, and marking out risky areas of potential deadly damage.
5. Improving and mapping seismic risk assessments throughout the area.
The New Madrid Fault Zone now appears to be about 30+ years past due for a very large magnitude 6.3+ earthquake. The last earthquake of this size occurred about 100 hundred years ago at Charleston, Missouri, on October 31, 1895 (the quake was a large magnitude 6.7). A 6.3 quake near the small city of Lepanto, Arkansas, on Jan. 5, 1843, was the next known quake of this size. More than 75% of the estimated timeframe for a magnitude 7.6 earthquake has gone by since the last huge quakes of this size occurred in 1812. Time is running out to get ready for another huge earthquake.