Geoscience Reference
In-Depth Information
7
The New Madrid seismic zone of the
Central United States
ROY VAN ARSDALE
Abstract
The central Mississippi River valley, within which the New Madrid seismic
zone (NMSZ) lies, has undergone a history of Precambrian microplate accre-
tion, Late Proterozoic Grenville orogenesis, Cambrian Reelfoot rifting, Late
Paleozoic Ouachita/Appalachian orogenesis, Cretaceous passage above the
Bermuda hotspot, and modest Cenozoic compression. Reelfoot Rift consists
of northwest-striking Proterozoic and the northeast-striking Cambrian faults,
which have undergone Neogene transpressive displacement that is apparently
driven by the N60
ES
Hmax
of eastern North America. NMSZ earth-
quakes are occurring along five reactivated Reelfoot Rift faults, three of which
are transpressive right-lateral strike-slip faults and two are reverse faults asso-
ciated with compressional stepovers between the strike-slip faults. A number of
models have been proposed for the NMSZ, but the model that best explains the
Holocene onset of the seismic zone is the Mississippi River valley denudation
model. In this model, Late Wisconsin entrenchment of the Mississippi River
reduced the vertical stress, which reduced the normal stress across the Reelfoot
Rift strike-slip faults and allowed them to slip. Quaternary displacement is not
restricted to the NMSZ faults and occurs on many of the Reelfoot Rift and its
outboard faults requiring an explanation for Quaternary faulting that encom-
passes a much larger area than the NMSZ. The denudation model appears to
explain the wide distribution of low-displacement Quaternary faulting in the
lower Mississippi River valley.
°
EtoN80
°
7.1 Introduction
The New Madrid seismic zone (NMSZ) is located in the central Mississippi River valley
within the states of Missouri, Tennessee, and Arkansas (
Figure 7.1
)
and is the most active
