NEW RESULTS ON LATE PLEISTOCENE FAULTING IN THE NEW MADRID SEISMIC ZONE

Topographic analyses and collection of geophysical data further document activity of two areas of Quaternary faulting on the New Madrid seismic zone fault complex margins. First, topography along the N/NE-striking Bootheel fault was analyzed using 10 m-resolution LiDAR. Treads of two Late Pleistocene fluvial terraces of the Mississippi River, 14-16 ka Kennett terrace and 12 ka Morehouse terrace, were used as structural datums that cross the Bootheel fault. We constructed best-fit polynomial trend surfaces of these terraces to assess long-wavelength deformation of their treads. Our results reveal a subtle 4 m-deep, 40 km-wide, 180 km-long, topographic trough parallel to the Bootheel fault. We interpret this trough as a subtle syncline in the northwestern block of the Bootheel fault that developed in response to Late Pleistocene down-on-the-northwest fault movement.

Second, a prominent topographic lineament is adjacent and parallel to the southeastern margin of the Reelfoot Rift. Previous paleoseismological studies suggest the southern segment of the lineament corresponds to steeply dipping strike-slip faults active in Late Pleistocene and Holocene, but the northern segment has not been rigorously investigated. A hypsometric analysis was performed along the northern segment order to assess whether any surface deformation related to faulting might have occurred along the lineament, and electrical resistivity tomography was used to image subsurface features. When combined, results from these analyses strongly suggest Late Pleistocene faulting is responsible for creating the northern segment of the rift margin lineament.