EVIDENCE FOR HOLOCENE DISPLACEMENTS ALONG THE BOOTHEEL FAULT (FORMERLY LINEAMENT) IN SOUTHEASTERN MISSOURI: SEISMOTECTONIC IMPLICATIONS FOR THE NEW MADRID REGION

The 135 km-long Bootheel lineament is a zone of en echelon, narrow, linear bands of sand blows, oriented N 24 ^oE in southeast Missouri and northeast Arkansas within the epicentral area of the 1811-1812 New Madrid earthquakes. Holocene faulting along the central part of the lineament locally produced about 3 m of vertical displacement of a <10.2 ky old Pleistocene braid-stream sand and at least 13 m of local dextral horizontal displacement of a Holocene paleochannel ca. 2.4 ky-old. The fault zone is less than 8 m wide where studied in detail. These observations suggest that the Bootheel lineament is a fault and we therefore suggest that it be renamed the Bootheel fault.

The area east of the Bootheel fault in our study area may have been uplifted a few meters during the Holocene, perhaps by a compressional popup at a 1.5 km-wide left-step restraining offset south of the study site. The very low level of seismicity recorded near the Bootheel fault suggests that it is either locked because of structural complexity or it is currently inactive. Based on the estimated 13 m of horizontal paleochannel displacement, an approximate 2.4 ky paleochannel age, and a mean earthquake recurrence interval of about 500 years, the local mean horizontal slip rate is estimated to be about 3.5 m per event. When displacement does occur on the Bootheel fault, it may subsequently load other faults, accounting for past earthquake sequences in the New Madrid region.