Four Major Holocene Earthquakes on the Reelfoot Fault Recorded by Sackungen in the New Madrid Seismic Zone, USA

Abstract

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.

Seismic Hazard Analyses From Geologic and Geomorphic Data: Current and Future Challenges

“…Many intraplate faults show evidence for strong temporal clustering of earthquakes and very low recurrence rates (10 to 100 kyr) (D. Clark et al, 2008, 2012, 2015; Cox et al, 2006; Crone et al, 1997, Craig et al, 2016; 2003; Gold et al, 2019; Stahl et al, 2016; Vallage & Bollinger, 2019). One intraplate faulting record that clearly demonstrates this behavior is from the Cadell Fault, in southeastern Australia.…”

“…No consensus exists on theories that explains intraplate earthquake occurrence and clustering (e.g., D. Clark et al, 2008Clark et al, , 2012Clark et al, , 2015Cox et al, 2006;Craig et al, 2016;Crone et al, 1997;Gold et al, 2019), though several, nonexclusive candidates exist. Calais et al (2016) argue that relatively simple models that can explain earthquake occurrence at plate boundaries, that is, models based on elastic rebound theory, are not applicable to intraplate regions and do not explain earthquake clustering occurring in these regions.…”

Quaternary Reelfoot Fault Deformation in the Obion River Valley, Tennessee, USA

“…Deformation rates of the Deweyville terrace are based on the observations that the Deweyville terrace surface postdates Peoria Loess deposition (e.g., preserved scroll bars, coring data presented in Van Arsdale et al., [1999]). Using the latest Peoria Loess age of 11 ka (Gold et al., 2019), the minimum apparent vertical deformation rate on the Deweyville terrace is ∼0.1 mm/yr. Paleoseismic records on the Reelfoot fault previously recognized earthquakes as early as ∼4 ka (Gold et al., 2019); therefore, this study significantly lengthens the paleoseismic record of fault slip on the southern section of the Reelfoot fault.…”

“…Previous identification of Quaternary surface deformation along the Reelfoot fault is limited to the northern section of the fault, but preservation is complicated by the migrating Mississippi River. The 1812 earthquake on the Reelfoot fault generated a broad, monoclinal scarp that, together with footwall subsidence, dammed the Reelfoot River, flooded the lowlands upstream, and created Reelfoot Lake (Figure 2) (Fuller, 1912;Russ, 1982;Stahle et al, 1992). The fold scarp bounding Reelfoot Lake is typically considered the southernmost extent of surface deformation from the 1812 event on the Reelfoot fault, although the fold scarp may have extended southeast to the bluff margin and has subsequently been eroded (Greenwood et al, 2016).…”

“…The blind Reelfoot reverse fault was one source of the 1811-1812 New Madrid earthquake sequence and is one of the few faults east of the Rocky Mountains with documented Holocene surface expression (Fisk, 1944;Fuller, 1912;Mueller & Pujol, 2001;Russ, 1979Russ, , 1982Van Arsdale et al, 1995). A key outstanding question for NMSZ hazard models is how far the Reelfoot fault extends to the south.…”