The New Madrid seismic zone of the Central United States - Intraplate Earthquakes - page 177

2008 ) . The major faults in the NMSZ are the southeastern Reelfoot Rift margin faults (Chiu
et al ., 1997 ) , the Axial fault, the New Madrid North fault (northwest Reelfoot Rift margin),
and the Reelfoot fault. The Reelfoot fault consists of two distinct segments: the Reelfoot
South fault is a left stepover linking the southeastern Reelfoot Rift margin and the Axial
fault, whereas the Reelfoot North fault is a left stepover linking the Axial fault with the
New Madrid North fault (northwestern Reelfoot Rift margin). Northeast of New Madrid,
Missouri, the northwestern Reelfoot Rift margin has 36 m of Quaternary displacement on
the Charleston uplift ( Figure 7.2 ) (Pryne et al ., 2013 ) .
The Commerce Geophysical Lineament is a very long basement feature ( Figure 7.2 ) that
may be an outlier fault of the Reelfoot Rift (Langenheim and Hildenbrand, 1997 ; Clendenin
and Diehl, 1999 ; Van Arsdale and Cupples, in press). Faulting in the Thebes Gap area of
Missouri (Harrison et al ., 1999 ) and Illinois (Nelson et al ., 1997 ) reveals that at least
this portion of the Commerce Geophysical Lineament (Commerce fault) is predominantly
a right-lateral strike-slip fault that has been active throughout the Phanerozoic and has
Quaternary movement. In the Western Lowlands (west of Crowley's Ridge) southwest
of Thebes Gap, Vaughn ( 1994 ) has identified four paleoliquefaction deposits (23,000-
17,000 yr BP, 13,430-9,000 yr BP, AD 240-1020, and AD 1440-1540) that may be due
to prehistoric earthquakes on a north-northwest-trending fault underlying the St. Francis
River ( Figure 7.2 ) .
Research also indicates Quaternary faulting east of the NMSZ (Parrish and Van Arsdale,
2004 ) . Cox et al . ( 2001a ) present evidence for Quaternary ground tilting based on analysis
of drainage-basin asymmetry that they attribute to basement block tilting in southwestern
Kentucky, western Tennessee, and northwestern Mississippi. Subsurface mapping of the
Upland Complex in western Kentucky and Tennessee reveals Quaternary east-west normal
faulting (Van Arsdale and Cupples, in press). Faulting has also been mapped south of
Memphis along the Big Creek fault zone (Spitz and Schumm, 1997 ; Harris and Sorrells,
2006 ; Harris, 2009 ) , immediately west of Memphis along the Meeman-Shelby fault (Hao
et al ., 2013 ) , and beneath Memphis that is Quaternary in age (Velasco et al ., 2005 ; Martin,
2008 ; Van Arsdale et al ., 2012 ) .
Immediately north of New Madrid, Missouri, is Sikeston Ridge ( Figure 7.1 ) , which
has been interpreted to be an erosional remnant of Pleistocene ancestral Mississippi River
incision. Although there is no evidence of surface faulting along the margins of Sikeston
Ridge, it is possible that Sikeston Ridge is an erosionally modified horst (Sexton, 1992 ;
Csontos, 2007 ) .
Regionally, we see other examples of compressional stepover zones within the Reelfoot
Rift (Csontos et al ., 2008 ) . The southern portion of Crowley's Ridge is a fault-bounded
block that has been interpreted to be a compressional stepover between the southeastern and
northwestern Reelfoot Rift margins ( Figure 7.2 ) . A stepover origin has also been proposed
for the sub-alluvial Joiner Ridge and its northwestern surface continuation of the Manila
High (Odum et al ., 2010 ) .
The Reelfoot fault hanging wall horst, Joiner Ridge, the southern portion of Crowley's
Ridge, and possibly Sikeston Ridge are nearly parallel uplifted blocks ( Figures 7.1 and