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:
- there are oil extraction sites that use fracking but don't produce much wastewater, and don't contribute much (or at all) to the earthquake cluster.
- there are oil extraction sites that don't use fracking and produce a lot of wastewater, that are major contributors to the earthquake cluster.
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.
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.
And Myths and Facts on Wastewater Injection, Hydraulic Fracturing, Enhanced Oil Recovery, and Induced Seismicity:
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).