As the readers here know, what happened in Michigan was not an earthquake, but what some people in Canada call a 'Frost Quake'. That's because it mostly happens in winter, when the frost causes the delamination of the highly stressed surface layers. Although freezing probably helps weaken the lower layers, these things happen any time of the year.
This picture shows a granite layer, but I see it mostly in limestone. They are quite a thump if you are near them when they let loose.