The Oklahoma earthquake swarms are an ongoing series of human activity-induced earthquakes affecting central Oklahoma southern Kansas, northern Texas since 2009. Beginning in 2009, the frequency of earthquakes in the U.S. state of Oklahoma rapidly increased from an average of fewer than two 3.0+ magnitude earthquakes per year since 1978 to hundreds each year in the 2014–17 period. Thousands of earthquakes have occurred in Oklahoma and surrounding areas in southern Kansas and North Texas since 2009. Scientific studies attribute the rise in earthquakes to the disposal of wastewater produced during oil extraction that has been injected more deeply into the ground.Fracking-Linked Earthquakes May Strike Far from Wells, Live Science, Becky Oskin, May 2, 2014. Retrieved 19 January 2016. Two most notable cases include water injection, geothermal-induced earthquakes in areas previously without any seismic activity - in Pohang, South Korea and St. Gallen, Switzerland.
Two of the most significant earthquakes in these swarms were the November 5, 2011 Prague earthquake east of the Oklahoma City area and the September 3, 2016 earthquake near Pawnee, north of Prague. The 2011 Prague earthquake, at reported magnitude 5.6, was at the time the strongest recorded earthquake in the history of Oklahoma. The 2016 earthquake was initially reported to be an identical 5.6 magnitude,Wilmoth, Adam. "Saturday's 5.6 magnitude earthquake ties record in Oklahoma," The Oklahoman, September 4, 2016. Accessed September 7, 2016. but this was later upgraded to 5.8, making it the strongest earthquake on record.Wilmoth, Adam. "Pawnee earthquake upgraded to magnitude 5.8," The Oklahoman, September 7, 2016. Accessed September 7, 2016. Simultaneously, the USGS upgraded the magnitude of the Prague earthquake to 5.7. Numerous seismologists had advised local residents of an even greater risk of earthquakes in 2014, by which time the number of earthquakes had increased to a dangerously high level. In response to the major increase in earthquakes in the Central United States, the United States Geological Survey (USGS) began developing a new seismic hazard model to account for risk associated with induced seismicity. By June 26, 2014, no fewer than six individual earthquake sequences in Oklahoma had been identified and named by the Oklahoma Geological Survey (OGS). Other swarms have been observed in south-central Kansas and North Texas.
In March 2013, a peer-reviewed paper published by a research team led by seismologist Katie Keranen at the University of Oklahoma in the scientific journal Geology reported that "the volume of fluid injected into the subsurface related to the production of unconventional resources continues to rise" and that there was a link between the "zone of injection and the seismicity" potentially triggering the Prague earthquake.via EBSCO On March 28, 2016 the USGS released the USGS National Seismic Hazard Map which concluded that the primary cause of the earthquake in Oklahoma in 2011 was pressure on fault lines from cumulative effects of injecting oil drilling wastewater under high pressure into the underground. Although the 2011 earthquake was the largest on record until that time, the USGS reported that the central and eastern U.S. (CEUS) had undergone the most dramatic increase in seismic activity in the United States since 2009 with an average of 318 earthquakes of magnitude 3.0 a year up from 24 a year from 1973 to 2008. In 2015 there were 1,010 earthquakes in the CEUS region. By mid-March 2016, there were already 226 earthquakes of magnitude 3.0 and larger in the CEUS.
Background The first earthquake known to have occurred within the boundaries of Oklahoma since the state was established occurred in September 1918 when a series of shocks was felt in El Reno, Oklahoma, the strongest of which was an estimated intensity V on September 10. On September 27, 1929, another tremor of intensity VI was centered in the same area and was felt in central and western Oklahoma; minor damage occurred in nearby areas and one chimney fell. The total affected area was approximately .
A magnitude 5.5 earthquake had occurred near El Reno on April 9, 1952 at 10:29 a.m. CST (16:29 UTC). At the time, it was the strongest earthquake ever recorded in Oklahoma. Most of Oklahoma was affected, as were parts of Arkansas, Iowa, Kansas, Missouri, Nebraska, and Texas. Damage was not extensive, but local residents were alarmed, and several thousands of dollars in damage occurred. Chimneys were toppled, walls were cracked, windows were broken, and bricks were loosened from buildings. In Oklahoma City, a crack measuring was found in the State Capitol following the earthquake. The earthquake, which occurred along the Nemaha Fault, had a maximum intensity of VII near the epicenter.
Scattered earthquakes occurred in Oklahoma between 1952 and 1969 with intensities as high as VII. Between 1978 and 2008, the average long-term rate of earthquakes was approximately two earthquakes of magnitude 3.0 or greater per year. However, in 2009, this number jumped to 20 with the beginning of several swarms of earthquakes in Oklahoma. Research suggests that most of the significant earthquakes in Oklahoma since the 1930s may have been induced by oil production activities, primarily waste-water disposal.
Earthquakes 2009–2010 The average number of earthquakes between 1978 and 1999 was 1.6 earthquakes of magnitude 3.0 or higher per year. This average dropped even lower between 2000 and 2008, with no year ever having more than three earthquakes of greater than or equal to magnitude 3.0 during the period. However, totals well above the 1978–2008 averages were recorded in 2009, with 20 earthquakes with magnitudes of at least 3.0 recorded. By the end of the year, Oklahoma County had seen its most active earthquake year since 1889, as recorded by the Oklahoma Geological Survey.
Earthquakes continued in 2010, with numerous earthquakes occurring in Central Oklahoma; among these is an earthquake which took place on October 13 in the vicinity of Norman. With a USGS-assigned magnitude of 4.4 Mw, it resulted in two fall-related injuries, and the USGS received felt reports from seven states. The year ended with an annual statewide total of 43 earthquakes of magnitude 3.0 or greater.
2011–2012
A rise in seismicity in Oklahoma was observed in 2011. Early on the morning of November 5, 2011, an earthquake with a magnitude of 4.8 struck an area east of Oklahoma City roughly centered between Sparks and Prague. At the time, it was the strongest earthquake associated with the rise in Oklahoma's seismicity. Less than a day later at 10:53 p.m., a 5.6 Mw earthquake occurred near the location of the preceding 4.8 magnitude earthquake, becoming the strongest earthquake observed with any of the swarms as well as the strongest earthquake in the history of Oklahoma. This also resulted in the reclassification of the magnitude 4.8 earthquake as a foreshock and the 5.6 magnitude earthquake as the mainshock. The earthquake received over 66,000 "Did You Feel It?" responses nationwide sent to the United States Geological Survey. It was believed that the earthquake had occurred along the Wilzetta Fault, also known as the Seminole Uplift. Following this earthquake, several portable seismograph stations were established by the USGS, OGS, and University of Oklahoma School of Geology and Geophysics to aid with detection of future earthquakes in the area. The 5.6 Mw mainshock was followed by a magnitude 4.8 aftershock slightly under two days later, and numerous other aftershocks occurred in the following months. Through the end of 2011, 64 earthquakes were recorded, nearly double the number recorded for 2010.
2012 saw a decrease in seismic activity in Oklahoma when compared to 2011, with a recorded annual total of 35 earthquakes magnitude 3.0 or greater, 29 fewer than recorded in the previous year.
2013–2014 On December 7, 2013, an earthquake occurred within the city limits of Oklahoma City in an area south of Lake Arcadia with a magnitude of 4.5 Mw. This was the strongest earthquake to occur in Oklahoma since the November 5, 2011 earthquake near the Prague–Sparks area east of Oklahoma City. For 2013, an estimated 109 earthquakes occurred according to the Oklahoma Geological Survey, a number substantially higher than in any previous year going back to 1978.
The 2014 total of 3.0+ magnitude earthquakes by May 2 was higher than the entire yearly total for 2013, at over 140 earthquakes. The number of earthquakes in Oklahoma increased by about 50% from October 2013 to May 2, 2014, prompting the United States Geological Survey to issue an uncommon "Earthquake Advisory" for Central Oklahoma warning of the elevated possibility of damaging, 5.5+ magnitude earthquakes. This was the first advisory in the United States ever issued east of the Rocky Mountains and remains effective.
On July 17, 2014, the United States Geological Survey released an updated map identifying seismic hazard for the continental United States. However, the earthquakes occurring in much of Oklahoma were not included in the creation of the map, for it is believed by the USGS that some degree of the earthquakes may have been induced by wastewater injection, and the map is meant to represent natural seismicity alone due to the unpredictable nature of earthquakes created by human industrial activities. Austin Holland of the OGS voiced concerns about the removal of the earthquakes in the map's creation, and he said "By removing them, we are underestimating the potential of serious seismic hazard in Oklahoma." William Ellsworth of the USGS responded by mentioning that the USGS was working on a new hazard model; "Everyone here thinks quakes, regardless of origin, need to be accounted for in our hazard model," he said.
The swarms, while initially located primarily further south, traveled northward from Central Oklahoma into Logan County in early 2014. Additional earthquake swarms initiated in north-central Oklahoma, including areas near Medford, Oklahoma. The latter swarms crossed into southern Kansas in 2013. Many earthquakes have also occurred in the southernmost part of Kansas since they began, with the most significant being a magnitude 4.9 earthquake on November 12, 2014, the strongest earthquake produced by the swarms since a magnitude 4.5 earthquake struck in Northeast Oklahoma City on December 7, 2013 almost a year earlier.
2015–2016
By the end of 2014, 567 earthquakes of at least magnitude 3.0 were recorded in Oklahoma, more than the number of 3.0+ magnitude earthquakes from the previous 30 years combined. In 2014, there were over twice as many earthquakes recorded in Oklahoma as in California, making Oklahoma the most seismically active state in the contiguous United States by a substantial margin. A review by EnergyWire examined earthquakes of greater than or equal to magnitude 3.0, and found that seismic activity in Oklahoma had been spreading northward into Kansas, which experienced a major jump in earthquakes from 2013 to 2014. As in southern Kansas, earthquakes increased in frequency in North Texas, with over 130 earthquakes occurring there from 2009 to early 2015.
For the first time, the United States Geological Survey decided it would include earthquakes believed to have connections to industrial activities in its National Seismic Hazard Map which sets standards for construction and insurance rates. According to USGS National Seismic Hazard Project head Mark Petersen, an updated version of the map would become available before the end of 2015. This marks a deviation from the past, with the USGS updating the National Seismic Hazard Map annually instead of every six years.