The Polar Vortex Might Be Causing 'Frost Quakes' in Chicago

It might be cold enough in Chicago right now to make the ground shake.Local news station WGN reported today (Jan. 30) that its viewers had heard "frost quakes" in the city overnight. And though the reports in Chicago are still unconfirmed, frost quakes are indeed a real thing.Frost quakes, or "cryoseisms," occur when water trapped underground freezes suddenly as the temperature drops, causing it to expand. (Water expands as it freezes.) All that rapidly expanding water underground can split rock