Most of the faults in Minnesota are at least a few hundreds of millions of years old, and are not very active. Just like the fault system that has triggered the recent quakes in and around Illinois, they are many things about them that aren't well understood. It is thought they are part of a failed rift system from when the North American tectonic plate began to split apart, and the faults remaining from that long inactive process still allow stress from the tectonic forces pushing the entire plate westward to trigger quakes at the interior of the plate where these faults weaken it, instead of just at the margins as is typical.
Minnesota has one of the lowest occurrence levels of earthquakes in the United States, but a total of 19 small to moderate earthquakes have been documented since 1860
University of Minnesota estimated average recurrence rates for Minnesota earthquakes as follows:
Magnitude 4 — 10 years
Magnitude 4.5 — 30 years
Magnitude 5 — 89 years
Magnitude 5.5 — 266 years
If earthquakes larger than magnitude 5.5 can occur in Minnesota, it is likely that their rate of recurrence would be many hundreds or perhaps thousands of years.