High-Resolution Seismic Imaging of Quaternary Faulting on the Crittenden County Fault Zone, New Madrid Seismic Zone, Northeastern Arkansas

The Crittenden County fault zone (CCFZ), located about 25 km northwest of Memphis, Tennessee, is a potential source of damaging earthquakes. To determine if geologically recent movement on the CCFZ has displaced Quaternary deposits, we acquired three very high-resolution compressional-wave seismic-reflection profiles across surface projections of faults that were observed on coincident [*][1]Mini-Sosie and Vibroseis seismic-reflection profiles. We used a 12-gauge shotgun and 5 kg weight drop as an energy source, with 100-Hz geophones spaced at 1.83 m and 0.25 m intervals, respectively. Reflections on the data are interpreted to be the Quaternary-Eocene (QE) unconformity whose depth varies between 40-50 m, a clay/sand interface whose depth varies between 25-40 m, and a reflection at 6-7 m depth (H reflector), which is probably a Holocene deposit. On one shotgun profile, the QE unconformity is deformed with about 5 m of relief and is faulted about 2 m, both down-to-the-west. On the second shotgun profile, the QE unconformity appears to be only faulted with about 1 m of throw. The amount of displacement on the QE unconformity is duplicated in the overlying clay/sand reflector on both shotgun profiles and the H reflector appears to be offset about 1 m down-to-the-west about 15 m west of the QE unconformity fault location on the shotgun profile. This fault appears to be a rootless, second-order feature that cannot be traced directly to the underlying main reverse fault. We interpret the down-to-the-west deformation on these reflections, which is opposite to the dominant flexure of underlying Paleozoic, Cretaceous, and Tertiary rocks to be caused by a bending-moment fault that formed in response to the monoclinal bulge caused by the subjacent main reverse fault. The deformation at and above the QE unconformity suggests that the CCFZ has been active during the latest Quaternary and may be a possible source of earthquakes. [1]: #fn-4

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