AIRBORNE LIDAR REVEALS COSEISMIC SACKUNGEN IN THE NEW MADRID SEISMIC ZONE (Invited Presentation)

Characterization of active intraplate faults in the U.S. and elsewhere poses several challenges due to low slip rates and infrequent earthquakes. In the New Madrid seismic zone, the paleoseismic record is further complicated by the humid climate, lateral migration of the Mississippi River, and anthropogenic modifications that erase evidence of surface deformation. Using bare-earth airborne lidar data, we identify and map ridgetop spreading features (sackungen) on low-relief bluffs and evaluate their relationship to the Reelfoot fault and other nearby structures. Sackungen typically occur in steep, high-relief terrain, but here are located within spatially extensive bluffs having only about 30-50 m of relief and simple, regionally homogenous geology. Sackungen occur within 15 km of the Reelfoot fault (with density decreasing with distance), are dominantly on the hanging wall, and are preferentially oriented parallel to fault strike. We interpret these sackungen to form and reactivate during large earthquakes on the Reelfoot fault due to strong coseismic shaking and static shear strain induced by fault deformation near the surface. Previous studies of coseismic ground failure in this area used aerial photography and field investigation to map large landslides triggered in the 1811-12 earthquake sequence and possibly an earlier earthquake, but these studies did not detect the sackungen, which are subtler landforms obscured by dense vegetation and disturbed by agricultural activity. In the New Madrid seismic zone, the investigation and analysis of sackungen provides an additional paleoseismic tool because sackungen can record episodic sedimentation resulting from earthquakes and potentially indicate fault orientation and slip type. This study demonstrates the importance of collecting and using high-resolution remote-sensing data in high and low slip settings over a broad spatial extent to evaluate both primary and secondary records of coseismic deformation. Similar sackung studies may be useful in places where established techniques, such as fault trenching, are difficult because of low slip rates, remote locations, or poor scarp preservation.