Quaternary Reelfoot Fault Deformation in the Obion River Valley, Tennessee, USA

Abstract

Blind reverse faults are challenging to detect, and earthquake records can be elusive because deep fault slip does not break the surface along readily recognized scarps. The blind Reelfoot fault in the New Madrid seismic zone in the central United States has been the subject of extensive prior investigation; however, the extent of slip at the southern portion of the fault remains unconstrained. In this study, we use lidar to map terraces and lacustrine landforms in the Obion River valley and investigate apparent broad folding resulting from slip on the buried Reelfoot fault. We compare remote surface mapping results with three auger boreholes in the ∼24 ka Finley terrace and interpret apparent warping as due to tectonic folding and not stratigraphic thickening. We combine our results with historical records of coseismic lake formation that indicate surface deformation dammed the Obion River in the 1812 CE earthquake. Older terraces (deposited at least 35–55 ka) record progressive fold scarps ≥1, ≥2, and ≥8 m high indicating a long record of earthquakes predating the existing paleoseismic record. Broad, distributed folding above the Reelfoot fault into the Obion River valley is consistent with a deep active fault tip along the southern reaches of the fault. Our analyses indicate the entire length of the fault (≥70 km) is capable of rupture and is more consistent with longer rupture scenarios.

Influence of Farallon Slab Loading on Intraplate Stress and Seismicity in Eastern North America in the Presence of Pre‐Existing Weak Zones

“…In the NMSZ, most faults are steeply dipping, between 70° and 90°, yielding low Coulomb stress values and thus stable faults, but the Reelfoot Fault dips between 30° and 44° (Csontos & Van Arsdale, 2008), placing it in an optimal orientation to be reactivated as a thrust fault in the local stress field. This fault indeed happens to be the site of one of the earthquake epicenters in the 1811–1812 earthquake sequence (Delano et al., 2021). The Reelfoot Fault is also the only fault to exhibit positive Coulomb stress values in each of our models (Figures 10a, 10d, 10g, 10j, and 10m), indicating a higher likelihood of fault reactivation.…”

“…Faults with unknown dip are assumed to have a dip of 90°. Purple stars mark earthquake locations; the three northernmost stars mark the locations of the most likely epicenters of the 1811–1812 earthquake sequence (Delano et al., 2021). For the WQSZ , fault locations are from Rimando and Peace (2021) and Lamontagne et al.…”

“…The NNW striking Joiner Ridge fault, which intersects the Axial Fault, has an unconstrained dip and thus was assigned a dip of 90°. However, this fault is identified as a thrust fault (Delano et al., 2021). If one were to assume a dip between 30° and 45° as in the case of the Reelfoot Fault, this fault would also exhibit high Coulomb stresses, and is in the vicinity of the remaining historical event just to the north on the Axial Fault.…”