Geoscience Reference
In-Depth Information
Figure 7.2 Reelfoot Rift faults and numbered locations of documented Quaternary faulting and liq-
Right-lateral shear across the Reelfoot Rift is responsible for the New Madrid seismic zone earth-
quakes, which occur along the Axial (northeast of number 16), Reelfoot South, and Reelfoot North
faults. Quaternary right-lateral shear on the rift faults is also causing uplift of the Lake County
uplift/Reelfoot North fault (RFN), Joiner Ridge (JR), Charleston Uplift, the southern portion of
Crowley's Ridge, and possibly the Meeman-Shelby fault. WRFZ, White River fault zone; BMTZ,
Bolivar Mansfield tectonic zone; OFZ, Osceola fault zone; CMTZ, Central Missouri tectonic zone;
GRTZ, Grand River tectonic zone; EM, Southeastern Reelfoot Rift margin faults; WM, Northwestern
Reelfoot Rift margin fault; AF, Axial fault (Cottonwood Grove fault); NMN, New Madrid North
fault; RFS, Reelfoot South fault; MS, Meeman-Shelby fault zone; CG, Commerce Geophysical linea-
ment/fault; BC, Big Creek/Ellendale fault; B, Bootheel fault; R, Risco fault (defined by seismicity);
M, Memphis, Tennessee; LR, Little Rock, Arkansas; NM, New Madrid, Missouri; C, Cairo, Illinois.
7.2 Geological history of the New Madrid seismic zone region
7.2.1 Precambrian
The NMSZ earthquakes are occurring beneath the flood plain of the central Mississippi
River valley. To more fully understand this area it is instructive to review the regional
geology and its history.
The Earth's crust beneath the Mississippi River valley has an average thickness of
