In all of recorded history, the Milwaukee area has been at the epicenter of an earthquake only once. This was on May 6, 1947 and luckily was only a short 4.0 magnitude quake, lasting only about 40 seconds. Although no major damage to infrastructure or buildings were reported, several downtown buildings were evacuated by frightened workers.
The sudden jolt threw the pens off of the two seismographs at the Marquette University physics department. The Rev. Joseph Carroll was at the time the head of the Physics Department at the university and it had the only seismographs in the area.
The Milwaukee Sentinel from May 7, 1947 reported:
Mayor Bohn called to see if the City Hall should be evacuated in case of another quake. Inspector Hubert Dax of the Police Department had the same question about the Safety Building.
Both were reassured by Father Carroll, who pointed out that Milwaukee “might not have another quake for 100 years.” He explained:
“The tilt of the rock of the lake shore, which probably caused the quake, will almost certainly not occur in the near future and may never occur again.”
A later quote gave a more interesting history of Wisconsin earthquakes showing how rare this event could be.
Yesterday’s quake is the only one on record in Wisconsin, Father Carroll added, and the only one even rumored in the state before the days of the seismograph was a light one in the 1750s.