New Madrid is a town in southern Missouri with a fault nearby.  It isn't
well known to the public, but seismologists know it well:
16 Dec 1811: Magnitude 8.6
23 Jan 1812: Magnitude 8.4
7 Feb 1812: Magnitude 8.7

Magnitudes are Richter Scale estimates.  For comparison the 1906 San
Franciscon quake on the San Andreas was 8.3.  So that 8.4 up there is
_big_.

But not the biggest.  The Mississippi ran uphill during some of those
shocks, and foot-high waves ran through the ground like surf.  Whee!