Iowa, though not typically associated with seismic activity, has experienced its fair share of earthquakes, shedding light on the region’s geological landscape and potential threats. Let’s delve into the history of notable earthquakes in Iowa and what they reveal about the state’s seismic vulnerability.
The 1867 Waverly Earthquake:
In April 1867, Iowa experienced its most severe earthquake, known as the Waverly earthquake. This event, with an estimated magnitude of 5.5, struck Waverly in Bremer County, northeastern Iowa, around 9:30 a.m. The tremors extended beyond Iowa, reaching neighboring states like Minnesota, Wisconsin, Illinois, Missouri, and Nebraska. Despite Iowa’s unfamiliarity with seismic events, this earthquake left its mark, causing significant damage by cracking houses, chimneys, and windows.
Particularly noteworthy was the creation of a 12-mile-long, 4-foot-wide fissure near the Cedar River, accompanied by rumbling sounds and flashes of light. This seismic event likely resulted from the reactivation of an ancient fault beneath Iowa’s sedimentary layers, possibly triggered by glacier loading during the Ice Age or regional tectonic forces associated with the New Madrid seismic zone in Missouri. The Waverly earthquake underscored Iowa’s susceptibility to seismic activity, hinting at the potential for future earthquakes.
The 1909 Colfax Earthquake:
On September 3, 1909, central Iowa experienced the Colfax earthquake, striking near Colfax in Jasper County around 5:40 a.m. With a magnitude of 5.1, its impact spanned approximately 200,000 square miles, affecting states such as Iowa, Minnesota, Wisconsin, Illinois, Missouri, Kansas, Nebraska, and South Dakota. While causing modest damage, including plaster and masonry fractures, and rattling windows and dishes, the earthquake also triggered landslides and sand boils along the Des Moines River.
Fault movements within Iowa’s Paleozoic sedimentary rocks likely caused this earthquake, influenced by various factors such as regional tectonic stresses or local activities like groundwater extraction or coal mining. The Colfax earthquake highlighted Iowa’s sensitivity to moderate seismic events, raising awareness of potential hidden faults within the region.
The 1984 Perry Earthquake:
The most recent widely felt earthquake in Iowa occurred on October 7, 1984, near Perry in Dallas County, registering a magnitude of 4.5. Tremors from this event spread across about 400,000 square miles, affecting multiple states. While not resulting in significant damage, it did evoke fear among residents and caused objects to sway or topple.
Seismometers nationwide recorded the earthquake waves, suggesting fault movement within Iowa’s Precambrian basement rocks. Regional tectonic forces or local activities like groundwater removal or oil and gas development could have contributed to this seismic event. The 1984 Perry earthquake underscored Iowa’s ongoing seismic activity and the potential for more substantial earthquakes in the future.
Conclusion:
In summary, although not commonly associated with earthquakes, Iowa has a history of significant seismic events, including the Waverly earthquake of 1867, the Colfax earthquake of 1909, and the Perry earthquake of 1984. These occurrences, stemming from fault movements beneath Iowa’s geological layers, underscore the state’s susceptibility to seismic activity and emphasize the importance of understanding and preparing for future earthquakes.