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Three sequences of well‐documented, major ~M7+ earthquakes (1811–1812, ~1450, and ~900 CE) in the New Madrid seismic zone, USA, contribute significantly to seismic hazard in the region. However, it is unknown whether this <550‐year recurrence interval has been constant throughout the Holocene given limited geomorphic evidence of prior earthquakes. We extend the record of paleoearthquakes along the Reelfoot fault via investigation of ridgetop gravitational failure features, interpreted as sackungen. The sackungen occur in bluffs along the eastern margin of the Mississippi River floodplain and are concentrated near (<15 km) the southwest dipping Reelfoot reverse fault. A paleoseismic trench excavated across sackungen at the Paw Paw site exposed four packages of colluvial sediment that postdate 30‐ to 11‐ka Peoria Loess. We interpret the colluvial packages to have been deposited following episodic failure of the sackungen as a result of strong ground motions from the following sequence of earthquakes: event 4, 1640 ± 1730 BCE; event 3, 270 ± 670 CE; event 2, 1430 ± 380 CE; and event 1, 1810 ± 50 CE (2 sigma). Event timing corresponds to previously documented earthquakes and represents the longest archive of paleoearthquakes on the Reelfoot fault. If the trenched sackungen record all major Reelfoot fault earthquakes, our observations in combination with prior investigations indicate a period of quiescence from at least 11 to 4.4 ka, followed by four major seismic events culminating in the 1811–1812 CE sequence. This clustered earthquake recurrence pattern helps place bounds on seismic hazard and geodynamic models in the New Madrid seismic zone. Key Points: Paleoseismic trench investigation of sackungen extends the paleoearthquake record of the Reelfoot fault, New Madrid seismic zoneThis study documents evidence for four prehistoric earthquakes since 11 ka, likely on the Reelfoot faultLongest earthquake record determined for Reelfoot fault indicates clustered earthquake recurrence [ABSTRACT FROM AUTHOR]

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 lidarThe sackung distribution and orientations suggest formation and/or reactivation during earthquakes on the Reelfoot faultSackung orientations could be used to infer the source fault for past earthquakes here and elsewhere [ABSTRACT FROM AUTHOR]

The 72-km-long Teton normal fault bounds the eastern base of the Teton Range in northwestern Wyoming, USA. Although geomorphic surfaces along the fault record latest Pleistocene to Holocene fault movement, the postglacial earthquake history of the fault has remained enigmatic. We excavated a paleoseismic trench at the Buffalo Bowl site along the southernmost part of the fault to determine its Holocene rupture history and slip rate. At the site, 6.3 m of displacement postdates an early Holocene (ca. 10.5 ka) alluvial-fan surface. We document evidence of three surface-faulting earthquakes based on packages of scarp-derived colluvium that postdate the alluvial-fan units. Bayesian modeling of radiocarbon and luminescence ages yields earthquake times of ca. 9.9 ka, ca. 7.1 ka, and ca. 4.6 ka, forming the longest, most complete paleoseismic record of the Teton fault. We integrate these data with a displaced deglacial surface 4 km NE at Granite Canyon to calculate a postglacial to mid-Holocene (14.4-4.6 ka) slip rate of 1.1 mm/yr. Our analysis also suggests that the postglacial to early Holocene (14.4-9.9 ka) slip rate exceeds the Holocene (9.9-4.6 ka) rate by a factor of 2 (maximum of 3); however, a uniform rate for the fault is possible considering the 95% slip-rate errors. The 5 k.y. elapsed time since the last rupture of the southernmost Teton fault implies a current slip deficit of 4-5 m, which is possibly explained by spatially/temporally incomplete paleoseismic data, irregular earthquake recurrence, and/or variable per-event displacement. Our study emphasizes the importance of minimizing slip-rate uncertainties by integrating paleoseismic and geomorphic data sets and capturing multiple earthquake cycles. [ABSTRACT FROM AUTHOR]