Swarms of earthquakes are occurring in areas not known for them, but where fracking is common. Hurm, we think, does Fracking cause earthquakes? It seems that injecting the produced water underground, as is common, can lubricate geologic faults, triggering an earthquake.
Oklahoma and southern Kansas, an area that's otherwise geologically quiet, have been subjected to routine earthquakes over the last several years. The same is happening in Ohio. In Oklahoma, the earthquakes began in 2009 and have been steadily increasing since. [USGS1] It's been discovered that Oklahoma had "hidden faults beneath the surface ready to pop". Fracking operations, and the disposal of produced water by underground injection, have lubricated those faults into activity. Another series of earthquakes in north Texas is causing the USGS to consider upgrading the earthquake risk in that area. [DallasNews] [NatGeographic] [USGS2] [USGS3] [Cleantechnica1] [TheVerge1] [Time1] [NatGeographic2] [ScienceDaily1] [CAFrackFacts] [TheTyee] [FAS1] [CNBC1] [FuelFix1] [ThinkProgress1]
USGS scientists have determined that large areas in the U.S. which formerly had few, or no, earthquakes are now seeing a "remarkable increase in earthquake activity". This is not the result of natural processes, says the USGS. [USGS4]
Instead, the increased seismicity is due to fluid injection associated with new technologies that enable the extraction of oil and gas from previously unproductive reservoirs. These modern extraction techniques result in large quantities of wastewater produced along with the oil and gas. The disposal of this wastewater by deep injection occasionally results in earthquakes that are large enough to be felt, and sometimes damaging. Deep injection of wastewater is the primary cause of the dramatic rise in detected earthquakes and the corresponding increase in seismic hazard in the central U.S.
Not all areas with fracking operations have earthquake activity. For example, North Dakota has lots and lots and lots of fracking operations but very few earthquakes. It's thought that for fracking to induce earthquakes, the injected water must find its way to a fault. Hence, if there's no geologic fault the fracking operations won't induce earthquakes.