Many geologists now believe the largest New Madrid quakes of 1811-12 were high 7 magnitude instead of 8's. See Magnitude - replaces Richter scale. Explains differences, and Mercalli intensity scale.
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Table 1.
Catalog of destructive earthquakes in the NewMadrid zone [
U.S. Geological Survey,
1990]
Date
Latitude
Longitude
Magnitude
Intensity
Location
December 16, 1811
36
90
8.2
11
NewMadrid
December 16, 1811
36
90
7.8
11
The same
January 23 , 1812
36.3
89.6
8.1
10{11
The same
February 7, 1811
36.5
89.6
8.3
11{12
The same
June 9, 1838
38.5
89
5.1
7{8
S. Illinois
January 4, 1843
35.5
90.5
6.4
8
Marked tree
October 8, 1857
38.7
89.2
5.1
7
S. Illinois
August 17, 1865
35.5
90.5
5.2
7
Marked tree
September 27, 1891
38.3
88.5
5.5
7
S. Illinois
April 12, 1895
37.0
89.4
6.8
9
Charleston
April 29, 1899
38.8
87.0
4.3
7
Vinsan
November 4, 1903
36.9
89.3
5.0
7
Missouri
August 21, 1905
36.8
89.6
4.9
7
Mississippi
May 26, 1909
42.5
89.0
5.2
7
Illinois
July 19, 1909
40.2
90.0
4.3
7
The same
September 27, 1909
39.5
87.4
4.7
7
Indiana
April 9, 1917
38.1
90.2
4.9
6{7
Missouri
November 27, 1922
37.5
88.5
4.4
6{7
Illinois
October 28, 1923
35.5
90.4
4.3
7
Marked tree
April 27, 1925
38.3
87.6
4.9
7
Indiana
May 7, 1927
35.7
90.6
4.8
7
Arkansas
December 16, 1931
34.1
89.8
4.1
6{7
Mississippi
February 2, 1962
36.6
89.7
4.2
6
NewMadrid
March 3, 1963
36.7
90.0
4.7
6
S. Missouri
October 21, 1965
37.8
91.1
4.6
6
N. Missouri
November 9, 1968
38.0
88.5
5.4
7
Illinois
January 1, 1969
34.8
92.6
4.3
6
Arkansas
November 17, 1970
35.9
89.9
4.1
6
Blytheville
September 15, 1972
41.6
89.4
4.1
6
Illinois
March 25, 1976
35.6
90.5
4.6
6
Arkansas
January 21, 1982
35.2
92.2
4.4
6
The same
June 10, 1987
38.7
88.0
5.0
6
Illinois
Note: Intensity of earthquakes is given according to the Mercalli scale.