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This sequence of three very large earthquakes is usually referred to as the New Madrid earthquakes, after the Missouri town that was the largest settlement on the Mississippi River between St. Louis, Missouri and Natchez, Mississippi.
We identified at least two cycles of pervasive meandering that were interrupted by channel-straightening responses occurring upstream of the Reelfoot fault scarp. These straightening responses initiated at 2244 BC +/− 269 to 1620 BC +/− 220 and AD 900, respectively, and each records initiation of a period of Reelfoot fault slip after millennia of relative tectonic quiescence. The second (or New Madrid) straightening response was triggered by the previously known AD 900 fault slip event, and this initial low sinuosity has been protracted until the modern day by the latter AD 1450 and AD 1812 events. The first (or Bondurant) straightening response began a period of several hundred to 1400 years of low river sinuosity which evidences a similar period of multiple recurrent displacement events on the Reelfoot fault. These Bondurant events predate the existing paleoseismic record for the Reelfoot fault. These data offer initial evidence that slip events on the Reelfoot fault were temporally clustered on millennial scales and, thus, offers the first direct evidence for millennial-scale clustering of earthquakes on a continental-interior fault
New Madrid fault shutting down.
A team from Purdue and Northwestern universities analyzed the fault motion for eight years using global positioning system measurements and found that it is much less than expected given the 500- to 1,000-year repeat cycle for major earthquakes on that fault. The last large earthquakes in the New Madrid seismic zone were magnitude 7-7.5 events in 1811 and 1812.
In it, instead of focusing on one major long-lived fault – like the San Andreas – we need to think of how different faults interact. Geologists are just starting to develop computer models of how it would work. An interesting question is whether the recent cluster of big earthquakes – the 1811-12, 1450, and 900 AD ones, is coming to an end. We can’t tell, but the longer the GPS data keep showing no motion, the more likely it seems The idea that earthquakes in the mid-continent are episodic, clustered, and migrating implies that we should think differently about earthquake hazards. Conventional thinking has been that the big danger is from earthquakes on the main New Madrid fault, although there was also some hazard from smaller earthquakes on other faults. The Federal Emergency Management Agency (FEMA) is pressuring communities in the region, which includes parts of Illinois, Indiana, Tennessee, Arkansas and Kentucky, to adopt building codes as strong — and as expensive — as California’s. Communities are grappling with how to react because it’s not clear if such stricter codes make economic sense. However, as the scientific case for this high hazard appears weaker, FEMA is now slowly starting to back down. We have a long way to go to fully understand Midwest earthquakes, but the new GPS data are a major step in the right direction