The New Madrid seismic zone of the Central United States - Intraplate Earthquakes - page 182

Figure 7.10 Model of the NMSZ combining sandbox analog and computer modeling (from Pratt,
2012 ) . Map view of predicted surface displacements caused by three N47°E upper-crustal faults
aboveaN28°E lower-crustal shear zone under a uniform N70°E regional compression. Seismicity
shown as white dots. M, Memphis, Tennessee.
( 1996 ) argue that body forces acting on the rift pillow contribute to the present-day stress
field, whereas Stuart et al .( 1997 ) suggest that slip along a subhorizontal detachment fault
near the domed top of the rift pillow creates a stress concentration in the upper crust
above the rift pillow dome. Pollitz et al .( 2001 ) propose that sudden weakening caused
by Wisconsin deglaciation caused the rift pillow to start sinking, which in turn initiated
a downward pull, leading to Reelfoot thrust faulting. Although the rift pillow has been
cited as a factor in causing the NMSZ, as discussed above, the rift pillow's age is in
question. The apex of the rift pillow underlies the “bull's-eye” of the Cambrian-Upper
Cretaceous unconformity beneath the NMSZ. (See the top of the Paleozoic animation at
www.geosociety.org/pubs/ft2009.htm [Csontos et al ., 2008 ; Van Arsdale, 2009 ] ). It seems
unlikely that this superposition is a coincidence, and this Cretaceous unconformity pattern