Hydraulic fracturing, commonly called fracking, is a way to extract natural gas from shale rock, by using a modern process to inject a high-pressure water mixture at the rock to release the gas inside. By all accounts it has been an environmental boon, responsible for causing energy emissions from coal to plummet back to early 1980s levels without causing energy prices to rise and harm poor people.
But two employees of a software development company and a Department of the Interior member say fracking is causing earthquakes, they just weren't felt by the public. Micro-earthquakes are quite common, they occurred millions of years before fracking did, but now sensors can detect them. Nearly 400 small earthquakes occurred between Oct. 1st and Dec. 13th, 2013, including 10 "positive" magnitude earthquake, which ranged from magnitude 1.7 to 2.2 between Oct. 2 and 19th. Hydraulic fracturing can create small earthquakes, of a magnitude in the range of negative 3 (−3) to negative 1 (-1), just like conventional drilling always has.
The positive magnitude ones coincided with hydraulic fracturing operations at nearby wells. The earthquakes were along an east-west trending fault that lies in the basement formation approximately two miles deep and directly below the three horizontal gas wells. The EarthScope Transportable Array Network Facility identified the first earthquakes on Oct. 2, 2013, locating them south of Clendening Lake near the town of Uhrichsville, Ohio. A subsequent analysis identified 190 earthquakes during a 39-hour period on Oct. 1 and 2, a few hours after hydraulic fracturing began on one of the wells.
The micro-seismicity varied, corresponding with the fracturing activity at the wells, they say. The timing of the earthquakes, along with their tight linear clustering and similar waveform signals, suggest a unique source for the cause of the earthquakes -- the hydraulic fracturing operation. The fracturing likely triggered slip on a pre-existing fault, though one that is located below the formation expected to confine the fracturing, according to the authors.
Glenda Besana-Ostman, with the U.S. Bureau of Reclamation, which manages government dams and canals, has said before that fracking is causing earthquakes and is co-author on this paper in Seismological Research Letters, an in-house publication of the Seismological Society of America.
"Hydraulic fracturing has the potential to trigger earthquakes, and in this case, small ones that could not be felt, however the earthquakes were three orders of magnitude larger than normally expected," said Paul Friberg, a seismologist with Instrumental Software Technologies, Inc. (ISTI) and co-author of the study. "As hydraulic fracturing operations explore new regions, more seismic monitoring will be needed since many faults remain unmapped."
Conveniently, ISTI provides geophysical support for seismic monitoring.