The strongest earthquakes ever recorded in the continental US were along the New Madrid fault. It remains active on a geological scale and its likely just a matter of time before the next monster earthquake, even though the last ones were just over 200 years ago.

Great computer animation at this site depicting the areas which would be hit if a 7.7 earthquake coming from the New Madrid fault should happen:

Computer Simulation of a Magnitude 7.7 Earthquake in the New Madrid Seismic Zone

https://earthquake.usgs.gov/scenarios/related/nmszM7.7.php

This animation shows the simulated ground motion of the Earth’s surface that could occur in the central U.S. region for a magnitude 7.7 strike-slip earthquake on the southern section of the New Madrid seismic zone. The simulation is based on a detailed geologic model of the central U.S. and is intended to show the general character of the long-period ground shaking expected for a large earthquake in the New Madrid seismic zone. It demonstrates the profound focusing effect the Reelfoot rift has on ground shaking produced by earthquakes. Further, the relatively unconsolidated material in the Mississippi embayment amplifies the ground shaking and also traps seismic energy to prolong the duration of ground  shaking.