Evidence for Late Quaternary Deformation Along Crowleys Ridge, New Madrid Seismic Zone

Abstract

The New Madrid seismic zone has been the source of multiple major (M ~7.0–7.5) earthquakes in the past 2 ka, yet the surface expression of recent deformation remains ambiguous. Crowleys Ridge, a linear ridge trending north-south for 300+ km through the Mississippi Embayment, has been interpreted as either a fault-bounded uplift or a nontectonic erosional remnant. New and previously published seismic reflection and shallow resistivity data show discontinuities at the ridge margins in Plio-Pleistocene strata, yet the timing of most recent faulting and the lateral extent of these faults remain unknown. To assess Pleistocene-to-recent tectonic activity of Crowleys Ridge, we perform landscape-scale geomorphic analyses, such as relief, slope, hypsometry, and drainage basin shape, on a 10-m digital elevation model (DEM). North-to-south variations in geomorphic indices indicate Pleistocene-to-recent tectonic uplift of the southern ridge. Moreover, mapping on a <1-m lidar-derived DEM reveals scarps on late Pleistocene geomorphic surfaces. The scarps are primarily located along the southern ridge, trend parallel to the ridge margin discontinuously for 0.1–1 km, and vertically offset <56 ka surfaces 0.4 m with up to 6 m of tilting. These landscape-scale patterns and scarps, integrated with discontinuities in the seismic reflection and resistivity data, provide evidence of low-rate (<0.2 mm/year) late Quaternary tectonic activity along the southern segment of Crowleys Ridge. The interpretations agree with recent tectonic models suggesting southern Crowleys Ridge is a compressional step over in a right-lateral fault system within the Reelfoot Rift.