Northeast-Oriented Transpression Structure in the Northern New Madrid Seismic Zone: Extension of a Shear Zone across the Reelfoot Fault Stepover Arm

Abstract High-resolution seismic-reflection profiles recently acquired 12 km northeast of the New Madrid seismic zone’s Reelfoot thrust and along the central axis of the Reelfoot rift, imaged steeply dipping N30°E striking faults that have uplifted and arched post-Paleozoic sediments in a manner consistent with a dextral strike-slip component of displacement. The subparallel fault strands have been traced 1.4 km between reflection profiles. In order to evaluate the structure’s potential regional scale, the strike was projected northeast 22 km to its intersection with a nearby in-dustry profile. At the intersection, this lower-resolution profile exhibits a discrete 0.75 km wide structure with style and offset similar to the high-resolution lines. The high-resolution images indicate the deformation extends above Paleozoic bed-rock, affecting the Late Cretaceous and Eocene Mississippi embayment sediments, as well as the base of the Quaternary. The Paleozoic and Cretaceous horizons show as much as 75 and 50 m of relief, respectively, with the middle Eocene and basal Quaternary disrupted 25 and 15 m, respectively. Geologic and geophysical logs from a borehole adjacent to the seismic lines constrain the depth, velocity, and stratigraphic interpretations. We interpret the faults as a minimum 34 km northeast extension of the Axial fault zone from a throughgoing intersection with the left-stepover Reelfoot thrust