A contribution to the seismic history of Missouri*

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Abstract
The status of Missouri as a state which contains active seismic areas has been a subject for speculation ever since the New Madrid earthquakes of 1811 and 1812. Local seismic research, however, was slow in starting, owing principally to the lack of available instruments to supply data sufficiently accurate for detailed work. Two events which gave great impetus to the progress of Missouri earthquake study were, first, the installation of the seismograph at St. Louis University in 1909, and second, the inauguration of the definite regional study plan which was proposed by Father Macelwane in 1925. The various stages in the development of regional earthquake study in Missouri have influenced the availability of data on the historical sequence of Missouri earthquakes. This paper, which is offered as a contribution to the seismic history of Missouri, reflects somewhat the growth of interest in local tremors. This growth, as shown by the increase in sources of data in the more recent years, is emphasized in order to avoid the misleading interpretation that the seismicity of Missouri is increasing. It is shown that although tabulation of the earthquakes, recorded by years, showed an increase in the yearly average from 0.6 in 1911 to 4.0 for the years 1930-1939, the latter figure seems the more nearly correct, and the former may be somewhat low owing to the incomplete data for the first half century following the New Madrid disaster. The earthquakes which have been felt in Missouri or which may possibly have been felt are listed by years, together with as many of the pertinent details as are available or space permits. By an examination of this list of shocks it can be seen that most of the earthquakes which have been felt in Missouri originate in more or less definite seismic districts. Six such districts are suggested for Missouri and they are called because of their locations the New Madrid, St. Marys, St. Louis, Hannibal, Springfield, and Northwestern Missouri seismic districts. Some of the earthquakes which have been felt in Missouri have apparently originated from seismic areas outside of the state boundaries. Four of these out-of-state areas are recognized, namely, the Centralia and Harrisburg districts in Illinois, the Anna, Ohio, region, and the Kansas-Nebraska Nemaha belt. It is shown that nearly 85 per cent of all the seismic activity of Missouri origin comes from two seismic areas: about 60 per cent from the New Madrid area, and about 25 per cent from the St. Marys fault region. A tabulation of the earthquakes by intensities indicates that most of the earthquakes of strong intensities also seem to come from the southeastern Mossouri area although only about 7 ½ per cent of the total of earthquakes recorded since 1816 have been strong enough to endanger life.

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