Geomorphic Evidence Of Deformation In The Northern Part Of The New Madrid Seismic Zone PDF Download

From interpretation of historical aerial photography and LiDAR imagery of northeast Arkansas, we identified a northeast-striking topographic lineament coincident with the trend of modern seismicity along the Axial Fault (AF) in the New Madrid Seismic Zone (NMSZ) (Fig. 1). The linear ridge extends 7.0 km across the landscape, is approximately 1 – 2 m higher than the topography to the east and west, and has en echelon trend segments. The anomalous topography appears to crosscut scroll bars, meander loops, and other geomorphic features along this portion of the Mississippi floodplain. This study sought to determine whether the lineament was of depositional or tectonic origin. We collected geophysical data including electrical resistivity (ERT), ground penetrating radar (GPR), magnetics, and seismic refraction across the ridge at three locations in order to image the subsurface of the structure of the ridge. ERT data show an abrupt discontinuity between higher and lower resistivity at depth beneath the western margin of the ridge suggesting a possible fault. Paleoseismic trenches excavated across the western side of the ridge revealed both a large, linear graben and a large linear sand blow with multiple sand units. The graben is 6.5 m wide and 1.0 m deep, and is filled with an organic-rich clay plug with many fractures along which root casts have formed and sand dikes have intruded. The liquefaction features include a main 1.8-m-wide, feeder dike that crosscuts a paleosol, several subsidiary dikes, and an overlying and related compound sand blow. These data suggest that the linear ridge graben pair and the parallel sand blow features may either be evidence for an active fault or be related to earthquake – induced lateral spreading and liquefaction. It is possible that the two features may both reveal and mask the presence of an active fault.