Geologic Impacts and Calculated Magnitudes of Historic Earthquakes in the Central United States

The New Madrid Seismic Zone, located in the central United States, produced five earthquakes in 1811-1812, 1843, and 1895, ranging from strong to major. A recurrence of its activity would cause substantial damage to the central U.S., but the magnitude of the most likely event is debatable. Accounting for 0.2 s spectral accelerations (SA) and peak ground velocities (PGV) with the local geologic conditions, this study offered methods for estimating the moment magnitudes (M) of these earthquakes. We analyzed 0.2 s SA and PGV and compared these data with the reported Modified Mercalli Intensities. Our estimates are M 7.6, 7.5, and 7.7 for the three 1811-1812 mainshocks in order of quake occurrence; M 6.2 for the 1843 Marked Tree, Arkansas; and M 6.7 for the 1895 Charleston, Missouri, earthquakes. These estimates are comparable to or exceed most previous approximations. Accordingly, potential liquefaction and resultant ground failure may affect most unconsolidated sediments throughout the central United States