A Revised Paleo-Earthquake Chronology on the Southeast Reelfoot Rift Margin near Memphis, Tennessee

Abstract

A trench was excavated across the southeastern Reelfoot rift margin for paleoseismic research purposes and for the 2011 Seismological Society of America national meeting field trip. The trench was parallel to and 6 m southwest of the Oldham trench described in 2006. In this 2011 trench, faulted alluvial fan stratigraphy and liquefaction deposits less than 4000 yr old were exposed. The trench revealed three tectonic deformation events. The first event (graben formation) and the second event (sand blow, minor faulting, and injection of sand dikes) both post-date a paleosol circa 4000 yr B.P. and pre-date a surficial colluvial soil deposit circa 2000 yr B.P. The third event (minor shallow liquefaction and surface deformation) post-dates a 2000-year-old surface colluvial soil. These age constraints allow this third event to be attributed to the 1811-1812 New Madrid earthquakes or a remotely triggered earthquake related to the 1811-1812 earthquake sequence. Although we cannot rule out that the deformation revealed in this trench was caused by earthquakes on other faults in the New Madrid seismic zone, our favored interpretation is that the deformation was caused by rupture on an underlying fault at the base of the Mississippi River bluff that was previously imaged in a shallow reflection profile near this site.