An earthquake on May 6, 1947, apparently centered just south of Milwaukee near the shore of Lake Michigan, caused only minor damage. There were no reports of injuries. The 4:25 a.m. CDT tremor shook buildings and rattled windows in many communities in a 7770 square kilometer area of southeastern Wisconsin. There were a few reports of broken windows at Kenosha (MM V), and residents of other communities reported that dishes and glasses had fallen from shelves. Some frightened Milwaukee residents ran into the streets in the belief there had been a serious explosion. The shock was felt in a 160 kilometer wide strip from Sheboygan to the Wisconsin - Illinois border and extended from the lakeshore to Waukesha, 40 kilometers inland.
Moderate shaking was reported at many places in Wisconsin from the strong earthquake centered near Charleston, South Carolina, on August 31, 1886. Intensity at Beloit, Janesville, and Milwaukee was estimated at V. A May 26, 1909, earthquake damaged many chimneys at Aurora, Illinois, and cause MM VII effects over a considerable area from Bloomington, Illinois, to Platteville, Wisconsin. Two more moderate shocks affected the same area on January 2, 1912. The first tremor was MM VI at Aurora, Freeport, Morris, and Yorkville, Illinois, and was followed by a lighter shock. Felt reports were received from Madison and Milwaukee.
An earthquake centered in eastern Missouri on April 9, 1919, affected a broad area from Wisconsin to Mississippi and from Kansas to Ohio, approximately 320,000 square kilometers. In the epicentral region between St. Louis and New Madrid, windows were broken and plaster cracked. Two shocks of short duration were reported felt at Madison (MM II).
Scattered felt reports in Wisconsin were noted from a major earthquake in the St. Lawrence River region near La Malbaie, Quebec, Canada, on February 28, 1925. The magnitude (M) 7.0 shock was felt over an area of approximately 5,000,000 square kilometers. Intensity at La Crosse and Milwaukee was estimated at III. Another strong Canadian earthquake (M=6 1/4) affected a large area of the northeastern and north-central United States on November 1, 1935. The 2,500,000 square kilometer felt area included most of eastern Wisconsin (MM I - III) and scattered points elsewhere in the State.
Two strong earthquakes near Anna, Ohio, on March 2 and 8, 1937, caused damage to buildings in the epicentral area and were reported felt over a six State region. The second shock was perhaps slightly stronger and more widespread than that of March 2, but the difference was not great. Both earthquakes were felt at Milwaukee; the latter tremor was also reported felt at Madison.
On November 23, 1939, a shock in southern Illinois having maximum intensity just short of damage (MM V) caused slight disturbances over an unusually large area (390,000 square kilometers). The intensity at Janesville, Wisconsin, was I - III. Medford, Milwaukee, and Racine felt minor vibrations from a moderate earthquake in south-central Michigan on August 9, 1947. Broken windows and considerable plaster and chimney damage were observed over a 30 kilometer radius from the epicenter, located near Coldwater, Michigan. The total felt area covered approximately 130,000 square kilometers and included portions of Illinois, Indiana, and Ohio.
The strongest earthquake in the central United States in 74 years occurred on November 9, 1968, in south-central Illinois. The shock was felt over an area of approximately 1,500,000 square kilometers, including all or portions of 23 States and southern Ontario, Canada. Measured at magnitude 5.3, maximum intensity reached VII in Illinois, Indiana, Kentucky, and Missouri. MM V was reported from Jefferson and Kenosha, Wisconsin, and MM I - IV, at Baraboo. LaCrosse, Milwaukee, Port Washington, Portage, Prairie Du Chien, and Sheboygan. Press reports indicated that the shock was also felt at Beloit, Janesville, and Madison.
Another earthquake in Illinois, about 500 kilometers north of the 1968 epicenter, caused slight damage at several places in Illinois, Indiana, Iowa, and Wisconsin. The September 14, 1972, tremor (M=3.7) was felt over 650,000 square kilometers, including Michigan, Minnesota, Missouri, Ohio, and the four States mentioned above. Cracked plaster (MM V) was noted at Kewaskum, Milton, Nashotah, and Zenda, Wisconsin. A report from Browntown noted that water pipes leaked after the shock.
Felt reports (MM I - III) were received from Kansasville, Mount Hope, and Trevor, Wisconsin, following a magnitude 4 3/4 earthquake on April 3, 1974, centered near the 1968 epicenter in southern Illinois. Within 1 hour or so, a number of tornadoes passed through the area affected by the earthquake. It is possible some of the reports confused the effects caused by the earthquake and those caused by the tornadoes.
Abridged from Earthquake Information Bulletin, Volume 10, Number 3, May - June 1978, by Carl A. von Hake.
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