75 Years Ago, Milwaukee Experienced the Most Severe Earthquake in Wisconsin History

In 1947, a historic earthquake struck southeast Wisconsin – but only for a split second.

It felt like a bomb went off. Dishes rattled in their cupboards, furniture shook, and people ran outside their homes and offices to get a view of what was happening from the street. But by the time anyone could catch their breath, Wisconsin’s biggest earthquake on record was over. 

At 3:27 p.m. on May 6, 1947, the earthquake jolted the southeastern part of the state for less than a second. “Our house shook like a leaf,” one Milwaukee resident told the Milwaukee Sentinel. Switchboards were jammed with frantic inquiries – was it an explosion? A weatherman working at the weather bureau told the Milwaukee Journal that the sensation didn’t seem deep enough to be an earthquake, and rather that it “felt as if one of the elevators fell down.” 

But the record was quickly set straight by the Rev. Joseph Carroll, a physics professor at Marquette University who had his eye on the university’s seismograph. However, the device was not able to get an accurate reading of the earthquake’s  magnitude. “Let me put it this way,” Carroll told the Journal that day, “The pens on the seismograph moved very slowly for the first 10th of a second. Then, in the second 10th of a second, both pens jumped completely off the paper record, putting the machine out of operation.”


 

FREE FINANCIAL ADVICE

Tune in for our next Women & Wealth webinar on Wednesday at noon. We’re talking about navigating your finances through life transitions. 


The experiences of local residents largely shape the memory of the 1947 earthquake today. Besides capturing a magnitude level on the Richter scale – which is determined by the readings on seismographs – scientists also gather accounts from people who experienced the earthquake to determine its intensity.

“Whenever there’s a big earthquake, people call in and say, well, this happened or this happened … my dishes fell, my house is leveled, whatever it is,” explains Brett Ketter, a seismologist at UW-Milwaukee. Those “felt reports” help seismologists piece together how the event happened, even without a clear reading.

The anomaly of the 1947 earthquake is that its epicenter was in seismically sleepy Wisconsin. “We’re nowhere near an active plate boundary – the one off to the east is in the middle of the Atlantic and the one off to the west is in California,” Ketter explains. There are active fault zones in Indiana, and quakes have radiated from there. But simply put, Wisconsin is “almost completely aseismic,” says Ketter.

Seismologists have ideas but no firm conclusions as to why the 1947 earthquake happened. A 2021 report in the journal Seismological Research Letters estimates that the earthquake was shallow, which is what caused it to jolt the region with such force. It likely had a 3.8 magnitude, which is categorized as minor. Pressure buildup on the plate beneath Wisconsin’s surface, potentially from water level changes in Lake Michigan, caused the ground to suddenly shake. 

Regardless of the cause, it’s highly unlikely that the event was caused by human activity, like an explosion. It has the hallmarks of a true earthquake, even without a clear seismic reading. “It’s too bad; I would love to have seen that record,” Ketter says. “Heck, I’d probably get [it] tattooed.


 

This story is part of Milwaukee Magazine‘s May issue.

Find it on newsstands or buy a copy at milwaukeemag.com/shop

Be the first to get every new issue. Subscribe.

Comments

comments