Which earthquake sequence began with the 1811 and 1812 shocks near New Madrid, Missouri?

The New Madrid earthquakes were a sequence of major shocks that began near New Madrid, Missouri, in 1811 and continued into 1812.

The sequence included powerful earthquakes on 16 December 1811, 23 January 1812, and 7 February 1812, along with many aftershocks. Shaking was felt across a huge part of the central and eastern United States, and reports described ground deformation, landslides, and changes in the course of parts of the Mississippi River.

The earthquakes occurred within the North American Plate, rather than at a plate boundary. This setting is called an intraplate earthquake zone. The New Madrid Seismic Zone remains active, although scientists cannot predict the exact time of a future earthquake.

Historical magnitude estimates are uncertain because instrumental recordings were unavailable, so modern values are inferred from written accounts and geological evidence.