Newly Recognized Quaternary Surface Faulting and Folding Peripheral to the New Madrid Seismic Zone, Central United States, and Implications for Restraining Bend Models of Intraplate Seismic Zones

A newly recognized thrust and nearby asymmetric anticline crop out 40 km north of Memphis, Tennessee, and they deform Eocene through Quaternary strata. These east–west-striking, south-verging structures are peripheral to the New Madrid seismic zone (NMSZ) of central North America, the source of M7+ earthquakes in 1811–1812. The thrust dips ∼20° N and has 55 m of throw in Eocene strata. An angular intraformational unconformity indicates most deformation was Eocene. The anticline’s limbs dip 7° N and 22° S and fold Eocene and Pleistocene strata. Pleistocene sediments are dropped at least 4 m into a graben along the fold axis. Holocene sediment is ponded upstream from the fold axis, suggesting Holocene activity. Based on outcrops, well logs, and seismic reflection, we interpret the anticline as a fault-tip fold above a splay of the thrust fault. We interpret these thrusts in the context of a previously published sandbox model of a restraining bend uplift, which we apply here to the Reelfoot Rift fault complex. Using the eastern rift margin as the strike-slip fault of the sandbox model, the periphery of the model uplift has an east–west-striking, south-verging oblique-slip thrust where the actual thrust and anticline crop out. These results suggest that young thrust faults may be common along the periphery of the NMSZ and similar active intraplate restraining bends, that the eastern margin of the Reelfoot Rift may have been a principal strike-slip fault of the restraining bend, and that the seismic zone was active as early as Eocene.