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

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 similar to 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.

Automated summary

Blind reverse faults are difficult to detect due to lack of surface rupture, such as the blind Reelfoot fault in the New Madrid seismic zone. By studying terraces and lacustrine landforms, researchers found evidence of broad folding caused by the buried fault's slip in the Obion River valley. Historical records of coseismic lake formation indicate the fault's significant deformation potential, with evidence of long earthquake history predating existing records.