![]() (b) Map of the distribution of sackungen and nearby faults within the eastern Mississippi River bluffs. Teeth indicate dip direction of a reverse fault arrows indicate sense of fault slip. Earthquake locations from Bakun and Hopper ( 2004). ( 2013), Johnston and Schweig ( 1996), and Stephenson et al. (a) Overview of the New Madrid (NMSZ) seismic zone in the Mississippi River valley with faults modified from Hao et al. We demonstrate that sackungen in the NMSZ contribute to the paleoseismic record and provide fault source information for integration into seismic hazard analyses. ( 2018), which revealed episodic displacement on sackung failure surfaces with ages that coincide with dated paleoearthquakes (location in Figure 1b). This study parallels a sackung trenching investigation by Gold et al. Over time, the term sackung has been used to describe a broad class of morphological features such as ridgetop grabens, linear fissures, and antislope scarps having several origin processes including sudden generation or reactivation from earthquakes (Gutiérrez et al., 2008 Hart, 2003 Jibson et al., 2004 McCalpin, 1999 Ponti & Wells, 1991). The term “sackung” (plural “sackungen”) was first used to describe a process inferred as deep bedrock creep accommodating ridge sag or gravitational spreading in mountainous regions (Varnes, 1989 Zischinsky, 1966, 1969). We use lidar to identify and map newly identified coseismic shaking features (sackungen) in western Tennessee and evaluate characteristics that constrain source faults and near-fault ground motions. The availability of high-resolution airborne lidar provides an opportunity to evaluate evidence of shaking-related surface deformation in the NMSZ. Studies of secondary shaking effects, such as dated liquefaction features or landslides, place constraints on the timing and/or extent of strong shaking, but these features cannot pinpoint earthquake source faults or slip mechanisms (Jibson & Keefer, 1988 Tuttle et al., 2005, 2002). Seismic surveys can constrain deformation at depth but typically lack sufficient resolution and ages needed to constrain earthquake timing and recurrence (Greenwood et al., 2016 Hamilton & Zoback, 1982 Odum et al., 1998 Van Arsdale et al., 1999). ![]() Paleoseismic techniques such as fault trenching in the NMSZ are hindered by thick sediment that buries and obscures surface faulting (Kelson et al., 1992, 1996 Russ, 1979, 1982 Russ et al., 1978). Evidence regarding source faults, earthquake size, rupture length, and epicentral locations remains ambiguous. However, direct evidence of earthquakes in the NMSZ is poorly preserved due to climatic, anthropogenic, and geomorphic factors, such as erosion and deposition from the proximal Mississippi River and surface modification from farming. Most recently, the NMSZ produced three M > 7 earthquakes during the winter of 1811–1812 (Fuller, 1912 Nuttli, 1973) as well as at least three other strong shaking events since ~2350 BCE (e.g., Holbrook et al., 2006 Kelson et al., 1996 Tuttle et al., 2002 Tuttle et al., 2005). The New Madrid seismic zone (NMSZ) in the central United States has the highest seismic hazard east of the Rocky Mountains (Petersen et al., 2014), but this elevated hazard is largely inferred from damaging earthquakes within the NMSZ that predate modern seismic instrumentation. ![]() 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.ĭetailed records of past earthquakes are critical for seismic hazard models (e.g., Petersen et al., 2014). The shaking features also provide constraints on the intensity of ground shaking near the Reelfoot 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. 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. ![]() We mapped ridgetop spreading and sagging on bluffs in northwestern Tennessee that likely form during large earthquakes. High-detail digital elevation maps reveal new evidence of strong shaking from earthquakes in the New Madrid seismic zone in the central United States.
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