Identification of possible Quaternary deformation in the northeastern Mississippi Embayment using quantitative geomorphic analysis of drainage-basin asymmetry

To investigate neotectonism in the Mississippi Embayment east of the New Ma drid seismic zone, we identified geomorphic domains that show evidence of g round tilting during Quaternary time. Transverse basin profiles were conver ted to two-dimensional vectors that denote channel position with respect to basin divides, These basin-asymmetry vectors record the net direction and degree of lateral migration of trunk streams. More than 2500 vectors were m easured and spatially averaged within 400 km(2) bins. This field of 300 mea n vectors delineates several domains that show preferred directions of stre am migrations possibly driven by ground tilting. The timing of stream migra tion was interpreted using across-valley distributions of Quaternary alluvi al terraces. Comparison of our mean vector field with subsurface structures suggests tha t some domain boundaries may be related to reactivated faults. Late Quatern ary activity is suggested for two northeast-striking faults of the southeas tern Reelfoot Rift margin. We acquired two seismic profiles showing near-su rface faulting beneath scarps that follow the domain boundary associated wi th one of these northeast-striking faults (Big Creek fault zone). Reelfoot thrust seismicity ends on the south against this fault, suggesting that the rift margin has dextral slip accommodating northeastward movement of the t hrust hanging wall. Our vector field also suggests Late Quaternary movement on the Reelfoot thrust and on two other northwest-striking faults, here te rmed the Hatchie River fault and the Wolf River fault. Several other weak d omains may imply minor elements of neotectonism. Our results demonstrate th at morphometric analysis of drainage-basin asymmetry can be an effective re connaissance tool within neotectonic settings.