The
1811–12 New Madrid earthquakes were an intense
intraplate earthquake series beginning with an initial earthquake of moment magnitude (7.5 -7.9) on December 16, 1811 followed by a moment magnitude 7.4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in
recorded history. They, as well as the seismic zone of their occurrence, were named for the
Mississippi River town of
New Madrid, then part of the
Louisiana Territory, now within
Missouri.