US seismologists have gradually suspected that the interior of the country is more likely to experience earth tremors than the typical spots on the west coast fault lines and they are mainly human induced earthquakes.
The U.S. Geological Survey accepts that gas and oil drilling is setting off hundreds of earthquakes. Most of these are too small to cause damage and many are difficult to detect because of their small scale
However, the study of this human-induced activity must continue, as it is believed that they could deliver magnitudes as large as 7, which was big enough in 1989 to kill 64 in San Francisco.
As the questions about the effects of Fracking continue, the US fracking centre of Oklahoma has seen the frequency of magnitude 3 or larger quakes change from 1.5 per year to 2.5 per day! The fracking process involves the injection of chemicals and water into rocks that can trigger fault lines, which cause quakes.
The largest earthquake in Prague, Oklahoma was magnitude 5.6 and caused injuries along with the destruction of 14 homes. The cause of this is still up for debate in court but a paper published in Geology places the blame with the waste water disposal that is injected deep into rocks at the end of the fracking process.