- © 2009 by the Seismological Society of America
The three principal New Madrid, central U.S., mainshocks of 1811–1812 were followed by extensive aftershock sequences that included numerous felt events. Although no instrumental data are available for the sequence, historical accounts provide information that can be used to estimate magnitudes and locations for the large aftershocks as well as the mainshocks. Several detailed eyewitness accounts of the sequence provide sufficient information to identify times and rough magnitude estimates for a number of aftershocks that have not been analyzed previously. I also use three extended compilations of felt events to explore the overall sequence productivity. Although one generally cannot estimate magnitudes or locations for individual events, the intensity distributions of recent, instrumentally recorded earthquakes in the region provide a basis for estimation of the magnitude distribution of 1811–1812 aftershocks. The distribution is consistent with a b-value distribution. I estimate Mw 6–6.3 for the three largest identifiable aftershocks, apart from the so-called dawn aftershock on 16 December 1811.