Neotectonics of the New Madrid Seismic Zone

Li and Schweig [1993] questioned the view that the Mississippi embayment and New Madrid seismic zone represents simple reactivations of the Precambrian Reelfoot rift. After observed S-waves that were converted from P-waves to improve their velocity model, Chiu et al. [1993] relocated events and found a simple California-type pattern with thrusting in a left step of a dextral strike-slip system. The important questions remaining concern the overall rate of deformation, and how (if) these faults connect to plate boundaries at each end. Liu et al. [1992] reoccupied triangulation stations with GPS and found rapid strain accumulation (0.08 rad/year) with a N67E shortening direction (in agreement with stress data) and a relative velocity of 5-7 mm/year across the network. Such a rate would obviously imply significant seismic hazard along strike from the 1811-1812 aftershock zone, so confirmation of the result by homogeneous geodetic methods should be a high priority. If it is confirmed, we may have a unique opportunity to study new faults in a relatively simple midcontinental setting.