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patterns as well as overall population figures. The population of the United States
was approximately 7,000,000 in 1811, with sizable numbers in the states of Ten-
nessee, Kentucky, and the region including the present-day states of Missouri and
Louisiana. The 1810 Census gives the population for several districts for which
felt reports are considered, including the District of St. Louis (population 5667),
Cincinnati (2540), New Orleans (24,552), Louisville (1357), and New Madrid
(2103). By 1811 some towns had grown beyond simple frontier villages, with solidly
constructed houses appearing by the turn of the century. The oldest brick building
west of the Mississippi was built in the town of Ste. Genevieve in 1804; this town
is along the Mississippi River valley north of New Madrid. This house and approx-
imately 50 others that predate the New Madrid sequence, are still standing today.
Although the New Madrid earthquakes were likely felt by hundreds of thousands
of people, spatial sampling of the intensity field was far from uniform. Especially
throughout the mid-continent, early American settlements clustered in proximity to
major river valleys. Significant amplification of shaking is expected at such sites,
and was in fact explicitly documented by several eye-witnesses to the New Madrid
earthquakes. As discussed at length by Hough et al. (2000), while every macroseis-
mic data set will include some effects that reflect sediment-induced amplification
effects, special care is necessary when interpreting 1811-1812 intensities because
of the especially biased nature of the data set.
In contrast, by 1880 the population of the United States had grown to over 50
million, and settlement patterns had changed dramatically, largely due to the de-
velopment of the U.S. railroad system. Railroad construction began in the U.S. in
the late 1820s and the first commercial lines began in the early 1830s. In 1838 the
railroads were designated as “post roads” by the U.S. Post Office; from this time
onward the railroads were used to move U.S. mail. This provided further impetus for
development of the rail system to the mid-continent and the West. As a consequence
of these developments, as well as the growing overall population, settlement became
more uniform throughout the former frontier regions. By the 1920s, early settlers
had also begun to recognize the pitfalls associated with life on the immediate river
banks, which included poor drainage, floods, and disease. The very earliest settle-
ments of the late 1700s and very early 1800s often were on fluvial sites, immediately
adjacent to rivers. New Madrid was built so close to the river bank that even before
the earthquakes, parts of the town regularly gave way under the continued assault
of river currents (Penick, 1981). By the time the Charleston earthquake occurred,
settlements had migrated inland, away from waterways.
Given the disparate size and distribution of the populations in 1811-1812 versus
1886, it is appropriate to consider the intensity distributions in more detail. As a
simple experiment, I winnow the 1886 intensity distribution down to only those
locations that are within 10 km of a point location for which an intensity is available
for NM1 (Figs. 6 and 7). Although one would ideally like use only the precise set
of locations for which an intensity value is available for NM1, in fact the locations
of early intensity observations are rarely precisely known. Using a buffer of 10 km,
the list of winnowed values for Charleston is about the same size as the number
available for NM1. In effect, this provides an indication of what the Charleston
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