Coseismic Sackungen in the New Madrid Seismic Zone, USA

High‐resolution lidar reveals newly recognized evidence of strong shaking in the New Madrid seismic zone in the central United States. We mapped concentrations of sackungen (ridgetop spreading features) on bluffs along the eastern Mississippi River valley in northwestern Tennessee that likely form or are reactivated during large earthquakes. These sackungen are concentrated on the hanging wall of the Reelfoot reverse fault and show a preferential orientation indicating ground failure normal to fault strike. These observations suggest that the sackungen record one or more earthquakes on the southern Reelfoot fault since the deposition of the ~30‐ to 11‐ka Peoria Loess and potentially constrain the minimum intensity of near‐fault ground motion. This study demonstrates that sackungen can be used to infer fault source and mechanism and, in combination with field‐based techniques, improve paleoseismic records and seismic hazard models. Plain Language Summary High‐detail digital elevation maps reveal new evidence of strong shaking from earthquakes in the New Madrid seismic zone in the central United States. We mapped ridgetop spreading and sagging on bluffs in northwestern Tennessee that likely form during large earthquakes. These spreading features are located near the compressional Reelfoot fault, are concentrated on the surface above the fault plane, and more commonly spread perpendicular to the fault. These observations suggest that these features record one or more earthquakes on the southern Reelfoot fault since the deposition of the underlying silt ~30,000–11,000 years ago. The shaking features also provide constraints on the intensity of ground shaking near the Reelfoot fault. This study demonstrates that ridgetop spreading features can be used to infer which fault generated past earthquakes and the type of movement that occurred on the fault, and, in combination with other research techniques, expand the record of past earthquakes and lead to improved seismic hazard models. Key Points Sackungen (ridgetop spreading features) are identified in the New Madrid seismic zone with new airborne lidar The sackung distribution and orientations suggest formation and/or reactivation during earthquakes on the Reelfoot fault Sackung orientations could be used to infer the source fault for past earthquakes here and elsewhere