|USGS, from a previous study|
A new paper in the Bulletin of the Seismological Society of America addresses what would happen today if there were a repeat of the historical New Madrid quakes (as occurs in my novel, Quake.) "More than eight million people living and working near the NMSZ would experience potentially damaging ground motion and modified Mercalli intensities ranging from VI to VIII if a repeat of the 1811–1812 earthquakes occurred today. Moreover, the duration of strong ground shaking in the greater Memphis metropolitan area could last from 30 to more than 60 s, depending on the magnitude and epicenter."
If you don't have access to scientific journals, a short article summarizing the paper is here