New Constraints on Reelfoot Fault Rupture, New Madrid Seismic Zone

Date: 4/25/2019

Time: 04:15 PM

Room: Pike

The Reelfoot fault in the New Madrid seismic zone is one of only a few documented Holocene-active faults in the central and eastern United States. Despite extensive geologic and geophysical investigation on the Reelfoot fault, historic and prehistoric fault rupture length remains uncertain, which is a necessary parameter for constraining potential earthquake magnitude. We investigate the southern extension of the reverse-slip Reelfoot fault in the Obion River valley, Tennessee, using high-resolution airborne lidar and field observations. We document evidence for broad folding and uplift of multiple late-Quaternary fluvial terrace levels that coincide with the projected surface trace of the Reelfoot fault. We test whether a monocline on the well-preserved Finley terrace (~25 ka) has a tectonic origin by comparing surface topographic profiles to stratigraphic constraints from a profile of three 7-m deep auger holes crossing the proposed surface projection of the fault. Surface profiles on the Finley terrace indicate >2 m of warping since terrace formation ~25 ka and agree with subsurface stratigraphy elevations from the auger profile. Older, higher terraces record progressive uplift and deformation on the Reelfoot fault hanging wall, which implies repeated earthquakes on this section of the fault. Modern floodplain constriction as well as historical and geomorphic records of repeated lake formation in the Obion River valley suggest coseismic fold scarp formation may have dammed the valley in the historic February 7^th, 1812 earthquake as well as earlier events. This, along with terrace deformation, implies a long-lived (>30 ka) earthquake record in the Obion River valley. Our results place bounds on the southernmost extent of surface deformation on the Reelfoot fault for 1812-type events, which informs future seismic hazard models for this region.

Presenting Author: Jaime Delano

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