Rachel Maddow on her show tonight showed a statistic that in 2011 when Pruitt became attorney general of Oklahoma, there were 34 earthquakes stronger than 3.0 on the Richter scale, and that grew to over 600 due to and that was later linked to fracking (injection of waste water).
Is it true that fracking (waste water injection) has caused significant increase of strong earthquakes (3.0 and higher) over the last, let's say 7 years, in Oklahoma.
There is induced seismicity in Oklahoma. There were 623 earthquakes above magnitude 3.0 in 2016. Some of these have been much stronger than 3.0, including a 5.8 magnitude earthquake in September 2016.
The induced earthquakes appear to have begun around 2009, and the problem has grown since then:
However, according to the US Geological Survey and other geologists, Oklahoma's induced seismicity is mainly caused by wastewater injection, not by fracking. The distinction is important because:
The distinction also matters because wastewater can be disposed of in a different state than the one in which the oil was extracted (see e.g. this, this), which raises a whole bunch of new issues for policymakers and legislators.
Per USGS:
Oklahoma now has more earthquakes on a regular basis than California. Are they due to fracking?
In a few cases, yes, but in most cases no. The majority of the earthquakes in Oklahoma since 2011 occur in areas where oil is being produced by pumping massive volumes of water out of naturally fractured formations to extract much smaller volumes of oil. Most of the wells used to access the oil are completed without being fracked. The natural formation water that comes to the surface with the oil is too saline to be released into the environment. Disposal by injection into deep formations is currently the most common method of disposal. Injecting large volumes of water into the deep sedimentary formations raises the pore pressure over large areas that can induce earthquakes.
Hydraulic fracturing does not play a key role in the increase in that (1) hydraulic fracturing does not typically induce felt earthquakes; (2) in Oklahoma, the location of the largest increase in seismicity, spent hydraulic fracturing fluid does not represent a large percentage of the fluids comprising disposed wastewater; and (3) oil produced from many fields with large volumes of produced water did not involve any hydraulic fracturing.
Sites that use the same method of oil extraction may produce different amounts of wastewater due to geological differences. For example, in Oklahoma:
the Bakken formation is also hydraulically fractured, but requires less wastewater disposal, has seen few to no induced earthquakes.
Almost every method of oil extraction produces some wastewater:
Most wastewater currently disposed of across the nation is generated and produced in the process of oil and gas extraction. As discussed above, saltwater is produced as a byproduct during the extraction process. This wastewater is found at nearly every oil and gas extraction well.
and in Oklahoma in particular, produced water is a major issue:
In many locations, wastewater has little or nothing to do with hydraulic fracturing. In Oklahoma, less than 10% of the water injected into wastewater disposal wells is used hydraulic fracturing fluid. Most of the wastewater in Oklahoma is saltwater that comes up along with oil during the extraction process.
And the USGS explains why:
Wastewater disposal wells typically operate for longer durations and inject much more fluid than hydraulic fracturing, making them more likely to induce earthquakes. Enhanced oil recovery injects fluid into rock layers where oil and gas have already been extracted, while wastewater injection often occurs in never-before-touched rocks. Therefore, wastewater injection can raise pressure levels more than enhanced oil recovery, and thus increases the likelihood of induced earthquakes.
This USGS Myths and Misconceptions page explains some of the differences between fracking and wastewater injection, and why wastewater injection and not fracking is the cause of most of the recent induced earthquakes in the central United States. You may also be interested in the video What's Behind the Earthquakes in Oklahoma? by Stanford geophysicist Mark Zoback (spoiler alert: it's wastewater injection, not fracking).
This answer is slightly tangential (as it's specific to Texas and not Oklahoma; which the cited research specifically noted as being geologically different). The main conclusion seems similar to @ff542's answer; in that yes there was increased amount of earthquakes but no the increase isn't attributable to fracking (but to fluid disposal in Class II disposal wells).
The Academy of Medicine, Engineering and Science of Texas (TAMEST) 2017 pre-publication study "ENVIRONMENTAL AND COMMUNITY IMPACTS OF SHALE DEVELOPMENT IN TEXAS" says in chapter on earthquakes:
- There has been an increase in the rate of recorded seismicity in Texas over the last several years. Between 1975 and 2008 there were, on average, one to two earthquakes per year of magnitude greater than M3.0. Between 2008 and 2016, the rate increased to about 12 to 15 earthquakes per year on average.
- Under certain unique geologic conditions, faults that are at or near critical stress may slip and produce an earthquake if nearby fluid injection alters the effective subsurface stresses acting on a fault.
- Mechanisms of both natural and induced earthquakes in Texas are not completely understood, and building physically-complete models to study them requires the integration of data that always will have irreducible uncertainties.
- To date, potentially induced earthquakes in Texas, felt at the surface, have been associated with fluid disposal in Class II disposal wells, not with the hydraulic fracturing process.
- The TexNet goals address an integrated research portfolio that considers seismicity analysis, geologic characterization, fluid-flow modeling, and geomechanical analysis.
