Minnesota's Largest Earthquake
The largest earthquake in Minnesota caused minor damage to walls and foundations of basements in Stevens county around Morris. Also felt in Iowa, North Dakota, and South Dakota. The earthquake was felt over an area of approximately 315,000 square kilometers including northern Iowa, Minnesota, southeastern North Dakota, and eastern South Dakota. Maximum intensity was VI. This is the largest earthquake ever instrumentally located in the state of Minnesota.
The last strongly felt earthquake in the State was a shock that occurred on September 3, 1917 near Staples with a maximum intensity of VI.
Besides eyewitness accounts of earthquakes in Minnesota, geologists look at rock layers for evidence of these events. They can see that different layers do not always lay flat on top of one another. There are folds and breaks. The shifting of the earth (known as earthquakes) caused the layers to move.
Geologists can also see evidence of earthquakes in Minnesota with the Midcontinental rift. This rift, running from Minnesota to Kansas, is the result of the middle of the North American continent splitting apart. Rifting is the opposite of a mountain range forming. Instead of rock material being pushed up to form a mountain, rock material falls down when a wide split in the land is made. Molten material from deep within the earth rises up to fill in the gap.