Abstract

The New Madrid earthquake, a succession of shocks in 1811 and 1812 in the northern portion of the Lower Mississippi Valley, caused earth waves, fissuring, sand blows, landslides, uplift, subsidence, and related phenomena over an area of thousands of square miles. However, considerable doubt is cast over the narrative accounts and evidence cited for assignment of the St. Francis Sunk Lands to the list of earthquake effects. Origin of these features as a result of alluvial drowning of several relict, braided stream channels by a Mississippi River crevasse channel appears to be a more tenable explanation. Excluding the sunk lands from consideration appreciably diminishes the southwestern extent of the area of discernible earthquake effects and helps subordinate the role of topographic and surface geologic features in calculating seismic-risk zonation in the area.

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