Large 19th Century Earthquakes in Eastern/Central North America: A Comparative Analysis - Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes - page 351

Fig. 7 Same as Fig. 3, but generated using only the winnowed Charleston data set shown in Fig. 6.
Intensity values for New Madrid earthquake are shifted upwards by 0.1 units for clarity
flood in the late 1700s resulted in substantial erosion of the river bank upon which
the town had originally been built (Brackenridge, 1817). According to a historian
whose father lived in Ste. Genevieve at the time of the earthquakes, many shocks
were felt in the town but they caused no damage (Rozier, 1890). This indicates MMI
values no higher than V for any of the events. Ste. Genevieve provides a further
illustration of the biases that can be associated with early archival records: the fact
that dramatic effects are more likely to be documented than less dramatic effects.
No account of the earthquakes from Ste. Genevieve is included in the compilation
of Street (1984). The brief account in Rozier (1890) was discovered by the author
following a focused archival search (Hough, 2004).
The accounts from Ste. Genevieve and Cincinnati thus suggest maximum cred-
ible MMI values of V and IV for hard-rock sites at distances of 160 and 560 km,
respectively. Considering the distribution of MMI values estimated by Bollinger
(1977), presumably at a given distance range, the low values provide an indication
of intensities at hard-rock sites (Fig. 8). At a distance range of 100-199 km, MMI
values range from a high of IX to a low of V, with just a single assignment of IV.
At a distance range of 500-599 km, values range from VIII to II-III, with just 7
values of II-III versus 19 for MMI IV. I thus suggest that V represents an estimate of
intensities at hard-rock sites at distances of 100-200 km, and an intensity of III-IV
for distances of 500-600 km. In both cases the estimated hard-rock intensities are
comparable to those available for the New Madrid events.
One can also consider the maximum distance at which NM1 and the Charleston
earthquake caused damage. As discussed by Bollinger (1977), the Charleston earth-
quake caused plaster to fall from walls in Chicago, Illinois, and Valparaiso, Indiana,