On June 30, 1947 (04h23m53s.1G.C.T.), an earthquake occurred in the Mississippi Valley near the confluence of the Meramec and Mississippi rivers a few miles south of St. Louis, Missouri. The shock reached a maximum intensity of VI (Modified Mercalli) and caused minor damage in a region about St. Louis. This earthquake occurred at a time when the Mississippi River at St. Louis was reaching the crest of one of the largest floods in history, a fact which partly accounted for the high degree of nervous reaction produced by the tremor, and which also provoked the question, “Did the flood trigger the earthquake?”

This paper reports the limited data on this earthquake and discusses the possible relations of the determined epicenter to previous local seismic activity and to geologic structure.

The conclusions reached in the paper are: (1) The earthquake originated in a basement zone of transitional structure which lies between the major regional tectonic elements. (2) There seems to be a genetic relation between this earthquake and epicenters which have been located along the Ste. Genevieve fault, on the Duquoin flexure, and on the northeastern Ozark flank. (3) The question, “Did the flood trigger the earthquake?” cannot be answered.

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