A sequence of powerful earthquakes struck the mid-Mississippi River Valley, central United States, in the winter of 1811-1812. The two largest probably exceeded the size of any continental western US earthquake. No fewer than 18 of these events were felt on the Atlantic seaboard or in Washington, DC (Nuttli 1987), at least 1000 km east, which implies moment magnitude M » 6.0-6.5 (Table 1).
Over time, this earthquake series has taken the name of the small riverboat town New Madrid, which lay at the heart of the epicentral zone and which in 1811 was the largest settlement on the river between St. Louis and Natchez. The name has proven apt, for New Madrid by happenstance marks the intersection of three of the six fault segments currently illuminated by microseismicity and believed to be rupture planes of the principal 1811-1812 earthquakes.
http://www.memphis.edu/ceri/compendium/enigma.pdf
I am well aware of New Madrid. I would like to see recent history of that region for comparison.