Abstract

The New Madrid North and Reelfoot Faults are believed to have ruptured during large-magnitude earthquakes on 23 January and 7 February 1812, respectively, based on the regional distribution of liquefaction, contemporary New Madrid seismic zone microseismicity, and historical accounts of earthquake-related damage. Although the location of the Reelfoot Fault generally is well constrained between the Kentucky Bend of the Mississippi River in Kentucky and the southeastern margin of the Mississippi Valley in Tennessee, the northern extent of the fault remains enigmatic in southeastern Missouri. This is equally true of the New Madrid North Fault, which has a postulated location based primarily on contemporary microseismicity and rupture scenario models of the 1811-1812 earthquake sequence. In this paper, we synthesize existing unpublished and published data with recently acquired subsurface and geomorphic information to clarify the locations of the Reelfoot and New Madrid North Faults in southeastern Missouri.

On the basis of this data synthesis, we interpret that the Reelfoot Fault trends northwest across the Kentucky Bend of the Mississippi River as a northwest-facing scarp coincident with Des Cyprie Slough near New Madrid, Missouri, and anomalous elevated topography on southern Sikeston Ridge northwest of New Madrid. Furthermore, Quaternary faulting and folding imaged from seismic-reflection profiles across Des Cyprie Slough coincide with bedrock structural lineaments, a northeast-trending band of contemporary microseismicity, and a distinct northwest-trending post-Tertiary change in alluvial thickness. We trace the Reelfoot Fault as much as several kilometers northwest of the Mississippi River, where it either dies out or steps north-northeast to merge with the New Madrid North Fault. The New Madrid North Fault appears to be expressed geomorphically as left-stepping, en echelon northeast-trending fractures preserved in Pleistocene glacial outwash material comprising Sikeston Ridge. The fractures coincide with Quaternary faults and folds, as well as deeper Cretaceous and Paleozoic faults and flexures, imaged in geophysical profiles. In summary, the surface locations of the Reelfoot and New Madrid North Faults directly west-northwest of New Madrid, Missouri are constrained by geomorphic, geologic, geophysical, and historical seismological data sets and reflect transfer of strain from the northeast-verging Reelfoot reverse fault to the northeast-striking, dextral New Madrid North Fault.

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