Pumping wastewater from shale gas operations deep underground was the likely cause of minor earthquakes recorded recently in Ohio, scientists said. A 2.7-magnitude earthquake rocked Ohio on Christmas Eve, followed by a 4.0-magnitude quake on New Year\'s Eve. Ohio authorities called on scientists at Columbia University\'s Lamont-Doherty Earth Observatory to conduct seismic studies of an area near Youngstown, Ohio, after nine small earthquakes were recorded last year. All of the quakes were recorded within a 5-mile radius of a wastewater injection well run by Northstar Disposal Services, Scientific American reports. Scientists with the Earth Observatory said the holiday quakes were triggered by operations tied to shale gas work in the area. John Armbruster, a lead scientist at the observatory, said the two quakes were centered within a half-mile of the injection well. Armbruster\'s team said the quakes were triggered by wastewater from shale gas operations that acted as a lubricant at a fault located about 1 mile underground. Ohio lawmakers called on shale operators to stop working in the region during an investigation into the quakes. Most criticism of shale gas has focused on the chemicals used in the process. A similar quake was associated with shale operations in Great Britain last year.