NEAR-SURFACE GEOPHYSICAL INVESTIGATION OF A HYPOTHESIZED QUATERNARY-ACTIVE SHEAR ZONE ACCOMMODATION: NEW MADRID SEISMIC ZONE

Strain accommodation and geographic fault location are two seismic hazard parameters, among others, poorly defined in the New Madrid seismic zone (NMSZ). A recent series of seismic-reflection profiles acquired 12-km northeast of the Reelfoot stepover and along the central axis of the Reelfoot rift imaged steeply dipping N 30° E striking faults with transpressional displacement. Projecting these features northeast 22 km to their intersection with the nearest available subsurface dataset (i.e. a low-resolution industry seismic reflection profile) found a discrete set of faults with similar characteristics. Conversely, the 12 km southwest back-projection of the faults intersects the Reelfoot stepover near the community of Proctor City (TN), where the Reelfoot scarp displays a distinct lateral discontinuity in an otherwise linearly coherent orientation. A prior low-resolution seismic reflection profile present at this location also exhibits a transpressional fault structure affecting the tops of the deeper Cretaceous and Paleozoic horizons; however, Quaternary stratigraphy were not resolved at either site. Newly acquired near-surface geophysical surveys across both these fault sets show Quaternary-active deformation based on local seismic stratigraphy. A third seismic-reflection dataset acquired along the projected strike of the fault zone exhibited similar deformation, providing additional evidence for a correlative relationship of a previously unknown 34-km-long northeast-oriented transpressional fault zone coincident with the hypothesized northeast continuation of the NMSZ’s southern Axial shear zone across the Reelfoot fault.