Geoscience Reference
In-Depth Information
Large 19th Century Earthquakes
in Eastern/Central North America:
A Comparative Analysis
S. E. Hough
Foreword For the understanding of seismogenesis as well as seismic hazard assess-
ment in the North American mid-continent, two historical events are of paramount
importance: the 1811-1812 New Madrid, central U.S,. sequence and the 1886
Charleston, South Carolina earthquake. Published estimates of magnitudes of the
four principal New Madrid earthquakes have ranged from M
7-8.75. In contrast,
published estimates of the magnitude of the Charleston earthquake have almost all
been within a range of Mw6.8-7.3. Upon cursory inspection, the macroseismic ef-
fects of the New Madrid mainshocks appear to be more severe at regional distances
than those of the Charleston mainshock. I compare the intensity distributions more
carefully, focusing on key indicators rather than the poorly constrained overall dis-
tribution of intensities. I conclude that the primary difference between the intensity
distributions of the Charleston and New Madrid earthquakes is that the former has
much better sampling, in particular of the low intensity field. These results sug-
gest that the largest New Madrid mainshocks were not substantially larger than the
Charleston earthquake.
1 Introduction
The earthquake sequence that struck the New Madrid region of the North American
mid-continent in 1811-1812 had remarkably far-reaching effects. By some accounts
the principal events in this sequence are among the largest—if not the largest—
earthquakes to have ever occurred in a so-called Stable Continental Region (SCR,
Johnston, 1996). Ground motions from the three principal events were felt by in-
dividuals as far away as Canada, New England, and at a number of locations
along the Atlantic coast (Mitchill, 1815; Bradbury, 1819; Fuller, 1912; Nuttli, 1973;
Penick, 1981; Street, 1984; Johnston, 1996). Contemporary accounts document
three principal mainshocks: approximately 0215 local time (LT) on 16 December
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