Unprecedented cold weather may have triggered "Frost quakes" in Chicago

Freezing cold in Chicago may have caused shaking related to cracking action in frozen ground.

The polar vortex that has descended on the United States has provoked freezing temperatures in Chicago. This phenomenon could be associated with the so-called "frost quakes."

"Frost quakes" or cryoseisms, despite having similar effects, are not related to typical earthquakes that are caused due to faults' displacement. They are provoked as a result of water freezing near the surface of the earth due to the presence of cold air above. In an extreme freezing environment, water may also freeze deeper in the ground. Freezing causes water to expand putting stress in the surrounding soil or rock-mass ultimately causing severe cracking. This cracking can sometimes cause a sudden but localized shaking.

At least 3 conditions must be satisfied for a frost quake to occur:

1. The ground must be saturated
2. No snow must be on the ground as it will prevent the underground water from freezing and
3. The temperature must drop enough to freeze the earth

According to Brent Hewett, a meteorologist at the NWS office in the Twin Cities region of Minnesota, cryoseisms have not occurred in the region because there is snow in the ground (condition 2 not satisfied).

On January 30, 2019, people in Chicago reported hearing loud noises and have "observed actual rivets in the ground after hearing the loud boom of a frost quake." The problem is that frost quakes cannot be verified. The induced cracks are not big enough and therefore difficult to be tracked down. Moreover, even if one crack is found it cannot be proven that it is associated with a cryoseism.

Charles Mott, a meteorologist at the National Weather Service (NWS) office working in Chicago stated that he hasn't noticed any frost quakes in recent days but it is possible that they have occurred.