Pennsylvania has over 19,300 shale gas wells, but no recorded seismic activity, according to Pittsburgh Tribune-Review. There’s a stark contrast between Pennsylvania and Ohio, where dozens of small earthquakes have occurred.

What makes Pennsylvania different is the state’s geologic make up. Salina, which is a thick layer of salt, keeps drilling from creating fault lines along the earth’s crust in Pennsylvania. The salina becomes thinner to the west of the Pennsylvania.

The most likely culprit for the quakes are wastewater wells. Ohio has 203 wells. 18 wastewater wells are being drilled in Ohio, while Pennsylvania only has seven total brine wells. In Ohio, wastewater wells are dug to depths of up to 10,000 feet, while in Pennsylvania, wells are dug to about 4,600 feet.

Via: Pittsburgh Tribune-Review > Pa. spared earthquakes from deep-shale drilling