Fracking and tremors

Fracking is known to cause very slight tremors when the fluid is injected into shale rock under high pressure. Drilling companies often send sensitive instruments called geophones into the drill holes to analyze the tiny tremors because they indicate whether the rock is fracturing as expected.

Quakes reported in Ohio, Oklahoma, and Arkansas in 2011 and 2012 were associated with wastewater injection wells (not fracking per se). The water first used in fracturing rock is retrieved and pumped into the injection wells. At more than 9,000 feet deep, the water is under high pressure that can build up over months or years; this pressure can cause earthquakes.

The 2011 earthquakes near UK's Blackpool were later linked to the hydraulic fracturing process itself. The quakes were thought to be caused the same way that quakes could be set off from disposal wells — by migration of the fluid into rock formations below the shale. Seismologists say that these deeper, older rocks, collectively referred to as the "basement," are littered with faults that, although under stress, have reached equilibrium over hundreds of millions of years.

Regulations
Regulations for injection wells (such as wells used for disposing fracking wastewater) are designed around protecting aquifers, not seismic risk. The federal Environmental Protection Agency, which regulates oil- and gas-related disposal wells unless its cedes its authority to the states, has no seismic requirements for its disposal wells. Drilling and disposal companies do not usually know where faults in deeper, older rocks beneath shale (the "basement") exist, as seismic surveys are costly, and states do not require them for oil or gas wells (although larger companies routinely conduct seismic tests as part of exploration).

According to E&E, oil and gas producers are exempt from a federal environmental law designed to prevent industrial waste injection wells from triggering earthquakes, although in 2012 the EPA began drafting suggestions for state regulators to minimize earthquakes caused by waste injection.

In July 2013 the EPA stated that operators should 'not operate' quake-linked disposal wells. It was reported that "EPA's examination of man-made earthquakes was undertaken by a technical working group of EPA and state officials in 2011. It has been shepherded by the staff of the agency's South Central Region, also called Region 6. The region has been caught in some of the fiercest debates about federal versus state regulation."

UK
On April 1 and May 27, 2011, two earthquakes with magnitudes 2.3 ML and 1.5 ML were detected in the Blackpool area in North West England. The seismic activity was immediately suspected to be linked to hydraulic fracture injections at the Preese Hall well, which was later confirmed by a study carried out by the operator, UK's Cuadrilla Resources. Cuadrilla concluded that the activity was caused by fluid injection into an adjacent fault zone during fracking.

In May 2011, Cuadrilla was forced to halt operations, leading to a temporary ban on fracking.

In April 2012, a UK government report recommended UK exploration of shale gas. The experts published the 2012 findings after reviewing a series of post-earthquake studies published by Cuadrilla Resources. The 2012 expert report suggested tighter rules on seismic monitoring and drilling surveys.

British Colombia
A 2012 report by the British Columbia Oil & Gas Commission, "Investigation of Observed Seismicity in the Horn River Basin," suggests tremors caused by fracking. According to the report, earthquake monitoring equipment in northern British Columbia, Canada, recorded 216 small earthquakes clustered in a small area around an ongoing fracking project in the northern end of the province. Of those earthquakes, 19 of them were rated between 2 and 3 on the Richter magnitude scale.

Focusing in on a subset of the earthquakes, the report states that:


 * "Eighteen [local] magnitude 1.9 to 3.0 events were selected from dense array microseismic plots. These events were selected because they were located adjacent to hydraulic fracturing stages and could be connected to a single stage fluid injection with some confidence. Evidence strongly suggests that all events were triggered by fluid injection at adjacent stages."

According to the Smithsonian, the report "found that eight of those earthquakes happened while the fracking was ongoing and that all eighteen happened within 24 hours of the fracking injections. The fracking-induced earthquakes happened when the fluid injection caused pre-existing faults within the Earth to slip. The strength of the earthquakes got bigger or smaller the closer or further the fracking was from the fault."

Ohio
In January 2012, Ohio regulators asked D&L Energy, a company that carries out fracking near Youngstown, to stop re-injecting waste water from hydraulic fracturing while an investigation was opened up into the cause of 12 earthquakes in the area (including a 4.0-magnitude quake on New Year’s Eve)--an area not considered seismically active. The site is at the bottom of a 9,200-foot-deep injection disposal well. Geological experts say the reinjected brine water could find its way into subterranean faults and force parts of the planet to separate, causing tremors. The earthquakes started in March 2011, about the same period that the major injection activities started.

On March 9, 2012, Ohio oil and gas regulators issued a preliminary report “on the relationship between the Northstar 1 Class II disposal well and 12 Youngstown area earthquakes.” The report found "a number of co-occurring circumstances strongly indicating the Youngstown area earthquakes were induced." In response, Ohio regulators said new safeguards would be added to Ohio’s existing disposal well regulatory framework, including prohibiting any new wells to be drilled into the Precambrian basement rock formation; mandating that operators submit extensive geological data before drilling; and implementing state-of-the-art pressure and volume monitoring devices including automatic shut-off switches and electronic data recorders.

In 2013, the Journal of Geophysical Research paper, "Induced seismicity associated with fluid injection into a deep well in Youngstown, Ohio," concluded that "the recent earthquakes in Youngstown, Ohio were induced by the fluid injection at a deep injection" and that the data "may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped."

Oklahoma
Oklahoma has seen a sharp rise in the number of earthquakes in the last few years. In August 2011, the Oklahoma Geological Survey examined a cluster of earthquakes in Oklahoma and found "that shortly after hydraulic fracturing began small earthquakes started occurring, and more than 50 were identified, of which 43 were large enough to be located. Most of these earthquakes occurred within a 24 hour period after hydraulic fracturing operations had ceased."

On April 18, 2012, University of Memphis scientist Stephen Horton released his findings that a 5.7 quake in November 2011 was "possibly triggered" by injection wells near the fault that ruptured. Horton found that 63 percent of earthquakes have occurred within 10 kilometers (about 6 miles) of a deep injection well, compared to a 31 percent chance of a random, natural earthquake happening within 10 kilometers of a deep injection well. He did note that the correlation between the location of the quake centers and the wells was complicated by the fact that some of the nearby injection wells had been in operation for 10 years, and the amount of fluid being injected has reportedly been on the decline for the last five years.

A 2013 study published in Geology linked Oklahoma's 5.7 earthquake to underground injection of wastewater, saying a decades-long time lag between injection and tremors is possible. Geologists placed seismometers in the area after the initial quake and were able to track fault rupture areas, which showed close proximity to disposal wells. According to the researchers: "we interpret that a net fluid volume increase after 18 yr of injection lowered effective stress on reservoir-bounding faults. Significantly, this case indicates that decades-long lags between the commencement of fluid injection and the onset of induced earthquakes are possible."

Arkansas
In Arkansas, shortly after fracking wastewater disposal wells were sunk in the state, that portion of the state was shaken by hundreds of quakes, the largest of which reached magnitude 4.7. The State Oil and Gas Commission was concerned enough about a probable link between disposal wells and the earthquakes that in July 2011 it ordered that one well be shut down, and it placed a moratorium on new ones in an 1,100-square-mile area. Three other disposal wells closed voluntarily. While small earthquakes are still occurring in the area, their frequency has declined substantially.

An article in Science later explained that "data from the seismometer network... painted a detailed picture of exactly how the injected wastewater triggered the [Arkansas] quakes. It was injected into an aquifer 3 kilometers down, where it increased the pressure of groundwater in the rock’s pores and fractures. From there the increased pressure due to injection spread through a previously unknown buried fault into the underlying rock, triggering quakes on the fault as it went."

Texas
A 2012 study published in the journal Proceedings of the National Academy of Sciences analyzed 67 earthquakes recorded between November 2009 and September 2011 in a 43.5-mile (70 kilometers) grid covering northern Texas' Barnett Shale formation. The study found that all 24 of the earthquakes with the most reliably located epicenters originated within 2 miles (3.2 km) of one or more injection wells for wastewater disposal. The study was headed by associate director and senior research scientist Cliff Frohlich at the University of Texas at Austin's Institute for Geophysics.

Before a series of small quakes on Halloween 2008, the Dallas area had never recorded a magnitude-3 earthquake, according to Frohlich. USGS data shows that, since then, there has been at least one quake at or above a magnitude 3 every year except 2010. Frohlich said the intensification in seismic activity in the Dallas area came the year after ground just south of (and thousands of feet below) the Dallas airport began to be inundated with wastewater from hydraulic fracturing. The injection well has been out of use since September 2011, but though water is no longer being added, lingering pressure differences from wastewater injection could still be contributing to the lubrication of long-stuck faults, according to Frohlich.

Three unusual earthquakes shook a suburb west of Dallas on September 29 and 30, 2012. The first quake was a magnitude 3.4, hitting a few miles southeast of the Dallas-Fort Worth (DFW) International Airport. It was followed 4 minutes later by a 3.1-magnitude aftershock that originated nearby. A third, magnitude-2.1 quake struck 24 hours later, with an epicenter a couple miles east of the first. No injuries were reported. Frohlich believes they are connected to wastewater disposal.

1963: Baldwin Hills Reservoir
On December 14, 1963, water burst through the foundation and earth dam of the Baldwin Hills Reservoir, a hilltop water storage facility located in metropolitan Los Angeles. The contents of the reservoir, some 250 million gallons of treated water that had filled the 20-acre basin to a depth of 70 feet, emptied within hours onto the communities below the Baldwin Hills, inundating a square mile of residences with mud and debris, and damaging or destroying 277 homes. Geologists say the disaster occurred as a result of displacement along faults in the unconsolidated sediments that underlie the reservoir, cracking the floor lining. On the day after the failure, it was apparent that major offset had occurred along what was to become known as the "Reservoir fault," the west side of the fault having moved relatively downward with respect to the east side.

Following the discovery in 1970 by geologist Douglas Hamilton of faulting and surface seepage of oilfield waste brines along the fault which traversed the reservoir, Hamilton and co-author Richard Meehan concluded in a 1971 article published in Science that oilfield injection for waste disposal and improved/enhanced recovery of oil, a new technology at the time, was a significant cause of the failure, triggering movements on a fault traversing the reservoir even on the day of the failure. The California Department of Conservation (DOC) has referred to hydraulic fracturing as a form of enhanced oil recovery.

1967: Rocky Mountain Arsenal
The Rocky Mountain Arsenal was a United States chemical weapons manufacturing center located in the Denver Metropolitan Area in Commerce City, Colorado. The site was operated by the United States Army throughout the later 20th century and was controversial among local residents until its closure in 1992.

RMA contained a deep injection water well that was constructed in 1961. It was drilled to a depth of 12,045 feet (3671 m). The well was cased and sealed to a depth of 11,975 feet (3650 m), with the remaining 70 feet (21 m) left as an open hole for the injection of Basin F liquids. For testing purposes, the well was injected with approximately 568,000 US gallons (2150 m³) of city water prior to injecting any waste. The Army said the injected fluids had very little potential for reaching the surface or usable groundwater supply since the injection point had 11,900 feet (3630 m) of rock above it and was sealed at the opening. The Army discontinued use of the well in February 1966 after a series of earthquakes in the area. According to the USGS, "In 1967, an earthquake of magnitude 5.5 followed a series of smaller earthquakes. Injection had been discontinued at the site in the previous year once the link between the fluid injection and the earlier series of earthquakes was established.” The well remained unused until 1985 when the Army permanently sealed the disposal well.

Recent studies

 * USGS, Are Seismicity Rate Changes in the Midcontinent Natural or Manmade? USGS, 2012. - The USGS study found that a "remarkable increase in the rate of M 3 and greater earthquakes is currently in progress in the US midcontinent" and "the acceleration in activity that began in 2009 appears to involve a combination of source regions of oil and gas production, including the Guy, Arkansas region, and in central and southern Oklahoma." The study concludes: "While the seismicity rate changes described here are almost certainly manmade, it remains to be determined how they are related to either changes in extraction methodologies or the rate of oil and gas production."
 * Ohio Department of Natural Resources, Preliminary Report on the Northstar 1 Class II Injection Well and the Seismic Events in the Youngstown, Ohio, Area, March 2012. - Found "a number of co-occurring circumstances strongly indicating the Youngstown area earthquakes were induced." There were 134 earthquakes in the region in 2011 measuring 3.0 or higher on the Richter scale – six times the average annual rate for any given year in the 20th century.
 * Austin Holland, Examination of Possibly Induced Seismicity from Hydraulic Fracturing in the Eola Field, Garvin County, Oklahoma, Oklahoma Geological Survey Open-File Report, 2011. - Examined a cluster of earthquakes in Oklahoma and found "that shortly after hydraulic fracturing began small earthquakes started occurring, and more than 50 were identified, of which 43 were large enough to be located. Most of these earthquakes occurred within a 24 hour period after hydraulic fracturing operations had ceased."

Magnitude
A 2011 study by geologist Arthur McGarr at the US Geological Survey in Menlo Park, California, calculated the possible maximum intensity of tremors from injecting fluid deep underground. Apart from fracking, such activities include the disposal of fracking fluids into disposal wells, as well as geothermal-power generation and carbon dioxide sequestration. McGarr and his team studied seven cases of quakes induced by fluid injection; the researchers found a proportional relationship between the volume of fluid injected and the magnitude of the earthquake. “If you inject about 10,000 cubic metres, then the maximum sized earthquake would be about a magnitude 3.3,” said McGarr. The work does not give the probability of an earthquake actually occurring: that depends on other factors, such as the strength and permeability of the rock.

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