Northern Extension of the Tennessee Reelfoot Scarp Into Kentucky and Missouri

Abstract

T he Reelfoot scarp in northwestern Tennessee is the surface expression of an east-verging fault propagation fold that overlies a southwest-dipping reverse fault. This fault is responsible for much of the current New Madrid seismicity and was probably the origin of the February 7, 1812, M 8.0 earthquake. Tectonic scarps in the Kentucky bend of the Mississippi River and at New Madrid, Missouri, appear to be a northwestern continuation of the Reelfoot scarp. Cores collected across the scarp in Kentucky where the topographic relief is 2.2 m reveal that the structural relief on a distinct subsurface fluvial sand bed is 4 m. One kilometer to the north the topographic relief is 3 m and structural relief is 4 m. Similarly, the scarp at New Madrid, Missouri, has 2 m of topographic and structural relief. These core data are compatible with trench observations to the south where the fold structure is reflected by the surface topography. This northern extension of the Reelfoot scarp into Kentucky and Missouri suggests a m a p p e d length of 32 km, nearly three times its previously defined length of 11 km. This 32 km length is more consistent with, but still too short for, rupture during a M 7.8 or M 8.0 earthquake. Coring data and microearthquake distribution suggest that the Reelfoot fault/scarp may continue southeast of its presently m a p p e d terminus.

AP- and SH-wave Seismic Reflection Investigation of the Kentucky Bend Scarp in the New Madrid Seismic Zone

“…The broad zones of deformation seen on the eastern (stations 36 to 123) flank of the fault F1A' is interpreted to represent compressional accommodation in response to the primary uplift on FIA" and F1B'. mately N30~ which is consistent with the attitude depicted by VanArsdale et al (1995). The fault projection is spatially consistent with the contemporary seismicity of the area, as well as historic accounts of waterfalls (Street and Green, 1984) upstream and downstream of New Madrid, Missouri, after the Feb. 7, 1812, event: corroborating evidence that the KBFS is a surface expression of that event.…”

“…The area lies within the broad structural framework of the Reelfoot rift and locally within the Lake County uplift (LCU), an active elongated topographic bulge that is believed to be associated with the contemporary seismicity in the central NMSZ (Russ, 1982). Specifically, the scarp is developed in Middle to Late Holocene sediments and is marked by oblique fluvial point bars, which suggests an origin not associated with fluvial erosion (VanArsdale et al, 1995). Figure 2 shows P-and SHwave walkaway profiles, the associated velocity/depth model, and the near-surface stratigraphy as observed from a 99 m borehole at the University of Kentucky's vertical strongmotion seismic array, VSAB.…”

Hammer-impact SH-wave seismic reflection methods in neotectonic investigations: General observations and case histories from the Mississippi Embayment, U.S.A.

“…11) across the New Madrid scarp shows a west-dipping reverse fault (located east of the scarp) that propagates upward from Tertiary (>40 m deep) to Quaternary sediments. This structural setting is almost identical to that imaged on the Reelfoot fault in west Tennessee (Sexton and Jones, 1986) where scarp topography and near-surface folding/extensional faulting (Kelson et al, 1996;van Arsdale et al, 1995) mimics folding and extensional faulting in the hanging-wall of the reverse fault. This is the first seismic image that clearly shows the continuation of the Reelfoot fault into Quaternary sediments, displaying the relationship between scarp topography and near-surface folding in the hangingwall of the Reelfoot fault.…”

“…1 for location), was shot across a topographic scarp that has been recognized as the northwest extension of the Reelfoot scarp (van Arsdale et al, 1995), last active during the M=8, February 7, 1812 New Madrid earthquake (Kelson et al, 1996). Based on shallow coring and paleoseismologic trenching, the Reelfoot scarp has been interpreted as a fault propagation fold above the west-dipping Reel- foot reverse fault.…”

A Two-Dimensional Numerical Model for Current Seismicity in the New Madrid Seismic Zone

“…An exception are the earthquakes that collectively define the New Madrid seismic zone (NMSZ), a subject of several recent investigations. These include tectonic and geological studies (Van Arsdale et al, 1995, 1999Johnston and Schweig, 1996;Van Arsdale et al, 1998;Guccione et al, 2000;Cox et al, 2001), potential field analyses (Hildenbrand, 1985;Rhea and Wheeler, 1994;Hildenbrand and Hendricks, 1995;Hildenbrand et al, 1996;Hildenbrand et al, 2001), seismicity evaluation (Chiu et al, 1992), estimates of the magnitudes of the 1811-1812 earthquake sequence (Johnston, 1996;Hough et al, 2000), paleoseismological investigations (Schweig and Ellis, 1994;Schweig and Tuttle, 1996;Tuttle et al, 1999;2002), seismic refraction studies Mooney et al, 1983), and geodetic studies (Liu et al, 1992;Snay et al, 1994;Weber et al, 1998;Neumann et al, 1999; Gan and Prescott, 2001). These studies have not only helped define the spatial extent, seismogenic features, and structural framework of the New Madrid seismic zone but have also refined the locations of seismicity, derived the recurrence rates of large earthquakes, and discovered evidence for neotectonic activity.…”