Last and largest New Madrid earthquake

Background. The New Madrid fault system produced a series of intense intraplate earthquakes beginning 16 December 1811, with further large shocks in January and February 1812. Four of the largest earthquakes in recorded North American history, with moment magnitudes estimated at 7 or greater, occurred within this three-month period.

The February Shock. On 7 February 1812 at 09:45 UTC (3:45 am local time), an earthquake struck with its epicenter near New Madrid. One source estimates its moment magnitude at 7.4–8.6, while another gives about 7.5; the largest estimate exceeds 8, but the figures are not reconciled across sources.

Aftermath and Population. Eliza Bryan of New Madrid, Missouri Territory, wrote an eyewitness account in March 1812. A Methodist chaplain traveling with Andrew Jackson's 1813 Natchez Expedition recorded that fissures near New Madrid looked awful on both sides of the river, that the earth continued to shake at times, and that the town's population had fallen from roughly 1,000 before the earthquakes to about 300, as many alarmed residents departed.

Longer-Term Evidence. Hundreds of aftershocks followed over several years. Dendrochronology on old bald cypress in Reelfoot Lake recorded fractures and rapid growth after inundation, while cypress in the St. Francis sunklands showed slowed growth in the half century after 1812—signals interpreted as evidence of the 1811–12 series.