Department of Geology
University of Kentucky
Lexington, Kentucky 40506
The purpose of this paper is to present a summary of the information obtained to date about the Mississippi river valley earthquake sequence of 1811-1812. The sequence of earthquakes that began at 02:15 A.M. local time on December 16, 1811, in what is present day NE Arkansas and SE Missouri, is the most significant seismic event to have occurred in central or eastern North America in historical times. The importance of this sequence has long been recognized in seismic risk analysis in central United States, and more recently, in the context of intra-plate tectonics. Several papers have been written on the 1811-1812 earthquakes--notable ones being the newspaper compilations by an anonymous author (1812) and Mitchill (1815), the observations and summary of effects of the earthquakes in the Ohio river valley by Drake (1815), the investigation of the meizoseismal area by Fuller (1812), and the body-wave magnitude scaling of the events by Nuttli (1973). Sources of information used by the authors cited, as well as additional sources of information not used by them, form the basis of this paper.
Modified Mercalli (MM) intensities based on accounts of the Mississippi river valley earthquakes of December 16, 1811, at 02:15 A.M. and 08:15 A.M., January 23, 1812, at 09:00 A.M., and February 07, 1812, at 03:45 A.M., are summarized in Table 1. Documentation to support the assigned intensity values listed in the table is given in Street (1980). The abbreviations F, NF and Insuf. used in the table stand for "felt", "not felt", and "insufficient information" respectively. Tabulated in the last column of the table under the heading of "General" are intensity values assigned to localities based on accounts that describe the effects of the earthquakes, but without reference to a specific date. Figures 1 thru 4 illustrate the geographical distribution of the intensity values for the four events summarized in Table 1, while Figure 5 illustrates the distribution of the MM intensity versus epicentral distances for the events. Points plotted along the bottom of the graphs in Figure 5 represent the "not felt" reports, while points plotted at the intensity II MM level represent the "felt" reports in Table 1.
Using the distribution of the MM intensities of the most thoroughly documented Mississippi river valley event--the 02:15 A.M. December 16, 1811, earthquake--and least squares, the following spatial attenuation of intensity relationship is determined:
where I is the averaged intensity at a distance R kilometers with a standard deviation of +/-1.75.
Figure 6 compares Equation (1) with the spatial attenuation of intensity curves by Howell and Schultz (1975), and by Gupta and Nuttli (1976); the latter two curves are scaled on the assumption that the 02:15 A.M. December 16, 1811, earthquake is an epicentral intensity XI MM event as suggested by Nuttli (1979). The three curves are similar in their attenuation of intensities, but differ in the level of predicted intensity at a distance R. This difference is due to the use of averaged intensity observed at distance R as done in this study, versus the use of the averaged epicentral distance to the various isoseismal contour levels as done by Howell and Schultz, and Gupta and Nuttli.
Documentation for the three events other than the 02:15 A.M. December 16, 1811, event in Table 1 is less complete, and regression analysis of the type used to derive Equation (1) results in unrealistic coefficients. Therefore to scale the intensity data as a function of R for the other three events, the coefficients of the R and log10R terms in Equation (1) were arbitrarily used. And with respect to the 02:15 A.M. December 16, 1811, event, the constant term in Equation (1) which includes the epicentral intensity, becomes 13.65 for the 08:15 A.M. December 16, 1811, event, 14.06 for the January 23, 1812, event, and 14.55 for the February 07, 1812, event.
Body-wave magnitudes can be estimated for the earthquakes by the technique developed by Nuttli (1973). Given the 7.2 mb body-wave magnitude calculated by Nuttli (1973) for the 02:15 A.M. December 16, 1811, event and the spatial attenuation of intensities for the four events, it is not difficult to show magnitudes of 7.0 for the 08:15 A.M. December 16, 1811, event, 7.1 for the January 23, 1812, event, and 7.3 for the February 07. 1812, event.
In conclusion, the purpose of this paper has been to further the documentation and understanding of the 1811-1812 Mississippi river valley earthquake sequence. The intensity levels and mbLg magnitudes for the January 23, 1812. and February 07, 1812, event have been more rigorously derived than heretofore published, and a fourth event, the 08:15 A.M. December 16, 1811, event has been shown to be a major event in this important earthquake sequence.
I wish to thank Otto Nuttli and Jim Zollweg for reviewing the material on which this paper was based and for their helpful suggestions.
This study was supported in part by the U.S. National Science Foundation under Grant PFR-7819765.
|Figure 1||Figure 2||Figure 3||Figure 4|
|Figure 5.1||Figure 5.2||Figure 6|
|- Ft. St. Stephens||V|
|- Ft. Stoddard||F|
|DISTRICT OF COLUMBIA|
Anonymous (1812). Account of the earthquakes which occurred in the United States, North America on the 16th of December, 1811, the 23d of January. and the 7th of February, 1812, Smith, Philadelphia, Pennsylvania.
Drake, D. (1815). Natural and statistical view, a picture of Cincinnati and the Miami country, illustrated by maps, with an appendix, containing observations on the late earthquakes, the aurora borealis, and the south-west wind, Cincinnati, Ohio.
Fuller, M. L. (1912). "The New Madrid earthquakes", U.S. Geological Survey Bulletin, 494, Washington, D.C.
Gupta, I. N. and 0. W. Nuttli (1976). "Spatial attenuation of intensities for central U.S. earthquakes", Bull. Seism. Soc. Am., 66, 743-751.
Howell, B. F. and T. R. Schultz (1975). "Attenuation of Modified Mercalli intensity with distance from the epicenter", Bull. Seism. Soc. Am., 65, 651-665.
Mitchill, S. L. (1815). A detailed narrative of the earthquakes which occurred on the 16th day of December, 1811, and agitated the parts of North America that lie between the Atlantic ocean and Louisiana; and also a particular account of other quakings of the earth occasionally felt from that time to the 23rd and 30th of January, and the 7th and 16th of February, 1812, and subsequently to the 18th of December, 1813, and which shook the country from Detroit and the Lakes to New Orleans and the Gulf of Mexico, Trans. Literary Phil. Soc., Vol. I, New York, New York.
Nuttli, 0. W. (1973). "The Mississippi valley earthquakes of 1811 and 1812: intensities, ground motion and magnitudes", Bull. Seism. Soc. Am., 63, 227-248.
Nuttli, 0. W. (1979). "Seismicity of the central United States", Geo. Soc. Am., Reviews in Engineering Geology, Vol. IV, 67-93.
Street, R. (1980). A compilation of accounts describing the Mississippi valley earthquakes of 1811-1812: Part I, Dept. of Geology, University of Kentucky, Lexington, KY, 247 p.