The USGS is studying the data and looking at earthquakes that have happened in Oklahoma. While researchers can’t pinpoint a cause at this time, the Saturday 5.6 Earthquake near Pawnee has some similarities to the 2011 quake that shook up Prague.

When the ground shakes here, it no longer catches people by surprise. But the fact that it shook twice overnight seemed to add an exclamation point to the release, just a few hours earlier, of the USGS's new hazard map -- the first to include the risk from induced seismicity, and the first to officially lift Oklahoma into the same overall risk category as California and Alaska.