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Seismicity

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Seismicity is the measure of the historical and geographic distribution of earthquakes. Seismologists study the frequency and intensity of earthquakes over a particular area. Seismographs are the instruments used to record earthquake vibrations that travel through the earth's interior.[1]

The term induced seismicity (or induced seismology) refers to seismic events that occur at higher than normal rates due to human activity. Induced seismic events (e.g., smaller earthquakes and tremors) can be the result of mining, damming rivers, or injecting fluids into underground wells.[2][3][4][5][2][3][4][6]

Background

How earthquakes occur

The three types of faults (cracks in the Earth's crust)

Earthquakes are vibrations under the Earth's surface. The vibrations are caused by the release of energy after two blocks of earth slip along a fault line (a fracture that exists between two chunks of earth). Stress is a force that acts on a plane and exists within fault lines. When an earthquake occurs, pre-existing stress is released. As two pieces of earth slip past one another, the energy (stress) is released as seismic waves that travel out along the Earth's interior surface. According to the U.S. Geological Survey, earthquakes can be caused by "a sudden dislocation of segments of the crust, by a volcanic eruption, or [an] event by manmade explosions." Because earthquakes represent the release of previously stored pressure beneath the earth, fault seismicity decreases over time as energy is released. Unless new energy is added to the system as tectonic plates shift, the existing energy under the Earth's surface remains the same or decreases over time.[7][8][9]

Measuring earthquakes

Earthquakes are measured in terms of magnitude, which is the maximum motion recorded by a seismograph. Two scales used to measure earthquake magnitude are the Richter scale and the moment magnitude scale. The Richter scale, which was developed in 1935, measures magnitude through the amplitude of waves recorded by a seismograph. The moment magnitude scale, developed in 1979, measures seismic events based on how much energy is released. According to the U.S. Geological Survey, seismologists consider the moment magnitude scale to be more accurate because it describes the size of a seismic event in greater detail and precision. Seismographs produce a seismogram, which is the visual record of the earthquake or tremor.[10][11][12][13][14]

In measuring an earthquake, scientists input the data from the seismogram into a logarithm to determine the earthquake's magnitude. This magnitude is rendered into whole and decimal numbers (for example, a 4.0 magnitude quake or a 3.5 magnitude quake). The magnitude figures are logarithmic; thus, each whole number increase represents a tenfold increase in measured amplitude. For example, a magnitude 6.5 quake (which is considered a strong earthquake by seismologists) would have 10 times more shaking power than a 5.3-magnitude quake (which is considered a more moderate earthquake by seismologists). According to the U.S. Geological Survey, an earthquake must be magnitude 3.0 or higher in order to be felt. The table below presents earthquake magnitudes (on the moment magnitude scale) compared to an abbreviated version of the Mercalli Intensity Scale, which is used to measure the shaking produced by an earthquake.[10][11][12][15]

Comparison of earthquake magnitude and expected outcomes
Magnitude Intensity
1.0 - 3.0 Earthquakes that are generally not felt
3.0 - 3.9 Earthquakes felt by some people at rest and on higher floors
4.0 - 4.9 Earthquakes felt by several people indoors and/or by most people
5.0 - 5.9 Earthquakes felt approximately by all people; these quakes may cause some damage to well-structured buildings and/or considerable damage to older buildings
6.0 - 6.9 Earthquakes that produce considerable damage, particularly within poorly constructed buildings; these quakes may collapse some buildings
7.0+ Earthquakes that can produce total damage of buildings, depending on the building’s construction
Source: U.S. Geological Survey, "Magnitude / Intensity Comparison"

Fracking and earthquakes

See also: Fracking in the United States

One debate involving hydraulic fracturing (also known as fracking) focuses on the potential role of fracking operations in contributing to or causing seismic activity.

In 2014, the U.S. Geological Survey concluded the following about fracking and felt earthquakes:[3][16][17]

“ USGS’s studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes. While hydraulic fracturing works by making thousands of extremely small 'microearthquakes,' they are, with just a few exceptions, too small to be felt; none have been large enough to cause structural damage. As noted previously, underground disposal of wastewater co-produced with oil and gas, enabled by hydraulic fracturing operations, has been linked to induced earthquakes.[3][18] ”
—U.S. Geological Survey

The following are examples of areas that experienced induced seismic events potentially linked to fracking activities. This information was last updated in November 2017.

British Columbia

Between April 2009 and December 2011, anomalous, low-level seismic activity was recorded within geographically confined and remote areas in the Horn River Basin near oil and gas activities. A June 2015 report produced by the British Columbia Oil and Gas Commission argued that the volume of injection fluid used during fracking in the Horn River Basin in northwestern Canada might have influenced local seismicity more than the injection pressure used; the report's authors found that background seismicity showed no observable change when the monthly volume of injected fluid was less than approximately 20,000 cubic meters. The report's authors argued that the first effect of increasing the volume of injected fluid was an observable increase in earthquake frequency but not an increase in earthquake magnitude. According to the report, the occurrence of seismic activity in the area was considered more probable if a well was located near a pre-existing fault and if the particular fault already experienced stress caused by the increased pressure of pre-existing fluids. A presentation about the study is available here.[19][20][21]

An example of a seismic wave that was caused by a land mine

Ohio

In March 2014, four seismic events (with a magnitude ranging between 2.2 and 3 on the Richter scale) were identified by the U.S. Geological Survey in Poland Township, Ohio, near a fracking operation. The Ohio Department of Natural Resources (ODNR) temporarily halted the operations and conducted an investigation, which concluded that there was likely a connection between fracking and the seismic events. These seismic events occurred on a previously unknown micro-fault. The ODNR announced it would require oil and gas operators to follow additional permit conditions and would begin to monitor and address induced seismicity in the state. The ODNR also said that it would work with private interstate oil and gas commissioners, states, and other stakeholders to share relevant data on induced seismicity and fracking. In addition, Ohio state regulators implemented a seismic monitoring system for certain disposal wells, particularly in areas where the surrounding geology could increase the likelihood of induced seismicity. Seismic monitors are used on a site-by-site basis; if induced seismic events are not detected prior to and after injection, the seismic instruments may be transferred elsewhere.[22][23]

Central and eastern United States

In 2016, the U.S. Geological Survey argued that wastewater disposal, rather than fracking, was the main cause of an increase in earthquakes throughout the central United States from 2009 to 2013. According to the agency, wastewater disposal wells raise pressure levels more than fracked wells. Larger amounts of fluid are used in wastewater disposal wells than in fracked wells; thus, wastewater disposal wells are more likely to produce induced seismic events than fracked wells, according to the agency. In addition, the agency argued that wastewater injection, and attendant seismic activity, typically occurs in rocks that have not been previously touched, whereas fracking involves injecting fluid into rock layers from which oil and natural gas have previously been extracted.[24][25]

In 2015, the Oklahoma Secretary of Energy and Environment established a website to document the state's response to induced seismic events. Other state agencies contribute data and other information to the site. The website includes a map of seismicity rates and disposal well locations. In addition, the Oklahoma state government implemented a seismic monitoring network to detect seismic events.[22]

Induced seismicity

Induced seismicity (or induced seismology) refers to seismic events that occur at higher than normal rates due to human activity. According to a 2012 report from the National Academy of Sciences, induced seismicity was first detected in the early 20th century. Human activities linked to induced seismic events include underground injection, oil and gas extraction, geothermal projects, mining extraction, underground nuclear tests, and the impoundment of reservoirs behind dams.[26]

Generally, induced earthquakes occur on a particularly stressed fault. Stress accumulates in the Earth’s surface through naturally occurring tectonic processes. The accumulated stress can be stored up for millennia. After fluids are injected into permeable formations during oil and gas operations, a limited amount of stress perturbation (outside influence) or a change in pore pressure (the pressure of fluids in the pores of a reservoir) can release the accumulated stress, causing an earthquake. Thus, injected fluids induce earthquakes primarily by changing stress conditions within and on faults. The stress then exceeds resistant stress in the fault, causing a slip (and thus an earthquake) on the fault. Other factors that can affect the likelihood of an induced earthquake include the magnitude of stress or pressure changes and the presence of particularly stressed faults more likely to produce seismic activity.[22][3]

According to a 2015 study published by States First (a group of regulators, governors, and policy analysts from oil and gas producing states), the Interstate Oil and Gas Compact Commission, and the Ground Water Protection Council, most U.S. disposal wells are not prone to induce earthquakes, though induced seismicity can occur under limited conditions in the presence of some injection wells, particularly wells near areas more likely to produce seismic activity.[22]

A 2015 study by the U.S. Geological Survey found that most injection wells in the United States do not cause felt earthquakes. Of the 35,000 disposal wells in 2015, as well as 80,000 oil recovery wells, approximately two to three dozen wells were known to have produced felt earthquakes. The study identified other factors needed for injection wells to produce felt earthquakes, such as stresses large enough to induce earthquakes, fluid pathways between injection points and faults, and changes in fluid pressure significant enough to produce an earthquake.[3]

A 2015 study by the Environmental Protection Agency (EPA) identified three factors needed for a disposal well to induce seismic activities: sufficient pressure buildup due to the disposing of fluids, a fault of concern (a fault that is significantly stressed), and a path allowing increased pressure to move from a well to a fault. According to the EPA, as of 2015 few disposals wells had produced earthquakes with a magnitude above 4 on the Richter scale (for comparison, an earthquake with a magnitude of 3 is similar to the passage of a nearby truck, according to the U.S. Geological Survey). In addition, the EPA found that no contamination of underground sources of drinking water had occurred related to injection-induced seismicity.[27]

The map below shows oil and gas plays and sedimentary basins in relation to wells associated with induced seismicity (click to enlarge). The data was collected by the U.S. Geological Survey and published in March 2016.

Map of oil and gas plays and sedimentary basins in relation to wells that have been associated with induced seismicity (Source: U.S. Geological Survey)[6] Click to enlarge.

Risk assessment

Two types of analysis are used by states, oil and gas operators, state and national geological surveyors, and private and university consultants to analyze whether an injection well may pose a hazard for induced seismicity and what potential risks—property damage or harm to individuals—could occur during an induced seismic event:[22][27]

  • Study of general patterns of seismicity: Studies of general seismic activity over a period of time are conducted to identify areas that may have atypical seismic activity correlated by location and time to injection well operations in a specific region. These studies provide a preliminary assessment of areas with a potential for induced seismicity. Other studies are conducted to elaborate further on the potential for induced earthquakes.
  • Event-specific studies: Several studies observe the geologic, seismologic, geophysical, and geomechanical factors that can influence the likelihood of an induced earthquake. Though it is difficult to assess whether an earthquake is induced or tectonic, or if an induced earthquake may be linked to injection well operations, the studies are used to develop risk management strategies and responses to potential earthquakes.

Stakeholders, including states, industry representatives, seismologists, engineers, and other experts at universities and at the U.S. Geological Survey, typically collaborate to collect and publish data on induced and tectonic earthquakes. These experts perform collaborative studies to determine whether seismic events near a disposal site occur alongside or soon after fluids are injected. The goal of these studies is to determine spatial and temporal correlations between induced seismic events and injections of fluid; the process is time-consuming and often complex. The studies seek to locate the seismic event, any particularly stressed faults that may have been reactivated, the temporal and spatial development of a seismic event, where a fault slip might have first occurred, and the subsurface stresses on or near the fault.[22][27]

Other information and data shared between stakeholders include the following:[22][27]

  • Historical and current seismic data recordings from the U.S. Geological Survey, state geological surveys, and private entities
  • Injection well locations, daily injection volumes, and aggregate injection volumes
  • Maximum injection pressure used daily at a well
  • Diagrams showing the well construction, the depths at which fluids are injected, and the formations where fluids are injected
  • Local factors such as population totals, nearby infrastructure, private and public structures in the area, and the location of dams and reservoirs.

Risk management

Stakeholders consider several risk management strategies to deal with induced seismic events related to new or existing wells. Risks are identified on a site-by-site basis and are mitigated in the following ways:[22][27]

  • For new wells, state permitting requirements may include review of the faulting or seismic history of a specific area.
  • State regulators may require well operators to adopt mechanisms to control, reduce, or eliminate the potential for felt seismic events in areas where potentially induced seismic activity may occur.
  • Operators may select a different location for new wells, avoid injecting fluids into certain areas, place wells outside of areas with faults and inject fluids in areas that will not disturb stress areas, avoid direct injection of fluids into specific faults, conduct seismic monitoring, and enact procedures to suspend injection operations if seismicity levels increase above a certain level.

Induced seismicity from 1965 to 2015

In an April 2015 study, the U.S. Geological Survey found that 17 areas had earthquakes that were likely caused by "fluid injection, mining, and conventional oil and gas production." The earthquakes identified in the study occurred between 1965 and 2015. As a result, the agency noted in its report that not all of these earthquakes could be associated with the increased use of fracking beginning in 2005. This information is summarized in the table below.[28][29][6][30][31][6]

Earthquakes likely caused by fluid injection, conventional oil and gas production, or mining
Location Nearby area Magnitude Date
Rocky Mountain Arsenal Near Denver, Colorado 4.8 August 1967
Rangely Northwestern Colorado 4.3 April 1970
Paradox Southwestern Colorado 3.9 January 2013
Greeley In the Denver Basin, Colorado 3.2 June 2014
Raton Basin New Mexico-Colorado border 5.2 August 2011
Dagger Draw Southeastern New Mexico 4.1 December 2005
Guy-Greenbrier Central Arkansas 4.7 February 2011
Oklahoma Central Oklahoma 5.6 November 2011
Northern Oklahoma and Southern Kansas Oklahoma-Kansas border 4.8 November 2014
Cogdell West-central Texas 4.5 June 1978
Fashing Southern Texas 4.6 October 2011
Timpson Eastern Texas 4.8 May 2012
Dallas-Fort Worth Near Dallas-Fort Worth, Texas 3.2 June 2012
Azle Northwest of Fort Worth, Texas 3.4 November 2013
Ashtabula Northeastern Ohio 3.9 January 2001
Youngstown Northeastern Ohio 3.7 December 2011
Brewton Alabama-Florida border 4.9 October 1997
Source: United States Geological Survey, "Incorporating Induced Seismicity in the 2014 United States National Seismic Hazard Model—Results of 2014 Workshop and Sensitivity Studies"

Injection wells

See also: Injection wells and Fracking
An example of a Class II injection well

Injection wells are cement-encased shafts in the ground used to store fluid or other substances. Some injection wells are shallow and used to store water and other non-hazardous liquids. Other wells are located deeper underground and used to store wastewater, salt water, and/or a mixture of water and chemicals. As of January 2014, the United States contained more than 150,000 Class II injection wells (wells that are used solely to inject fluids during oil and natural gas production); approximately 40,000 of these wells were waste fluid disposal wells for oil and gas operations, according to the U.S. Geological Survey. The remaining wells were enhanced recovery wells (where fluids are injected to recover residual oil and natural gas) and storage wells for liquid hydrocarbons (generally as part of the U.S. Strategic Petroleum Reserve). According to an agency report in January 2014, "Only a small fraction of these disposal wells have induced earthquakes that are large enough to be of concern to the public."[3][4][6][32]

History and regulation

The use of injection wells to dispose of waste from oil and natural gas extraction began in the 1930s in Texas. Oil producers found that salt water could be re-injected into a reservoir to maintain pressure. During the 1950s, more states began to regulate discharges into injection wells. Under the Clean Water Act of 1972, the federal government required states to issue permits for oil and gas operators that discharged water and chemicals into injection wells.[33]

Further injection well regulations were adopted in 1974 when Congress passed the Safe Drinking Water Act. The act requires the U.S. Environmental Protection Agency (EPA) to operate an underground injection control program. The EPA and authorized state agencies regulate injection wells depending on the kinds of waste injected and the depth at which this waste is injected. Under the act, the EPA is prohibited from prescribing regulations that may impede or interfere with the underground injection of fluids during oil and gas production unless the regulations are adopted to protect underground drinking water sources from such injections. In addition, the act requires the EPA to accommodate existing state regulatory programs covering underground injection wells and avoid regulations that may disrupt a state program's operations.[33]

Oil and gas operators are not required to apply for a permit if a well is authorized by a federal rule. All other wells must be approved through a permit issued by the EPA or an authorized state agency before they can be installed and drilled. Permit requirements and conditions depend on the type of well, the kinds of material injected, the geological features of the area, and other factors. Oil and gas operators must submit inventory information about their wells to the EPA or an authorized state agency and keep their own records. All wells regulated under the underground injection control program can be inspected by EPA or state government personnel.[34][33]

Map of areas with human-induced earthquakes that the USGS argued are not related to "fluid injection, mining, and conventional oil and gas production."[6]
Map key

Recent news

The link below is to the most recent stories in a Google news search for the terms Earthquakes injection wells. These results are automatically generated from Google. Ballotpedia does not curate or endorse these articles.

Seismicity - Google News

See also

External links

Footnotes

  1. ↑ U.S. Geological Survey, "Earthquake glossary - seismicity," accessed April 27, 2015
  2. ↑ 2.0 2.1 U.S. Department of Energy, "Induced Seismicity," accessed April 27, 2015
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 U.S. Geological Survey, "Man-Made Earthquakes Update," January 17, 2014 Cite error: Invalid <ref> tag; name "USGS" defined multiple times with different content Cite error: Invalid <ref> tag; name "USGS" defined multiple times with different content
  4. ↑ 4.0 4.1 4.2 National Public Radio, "How Oil and Gas Disposal Wells Can Cause Earthquakes," accessed June 2, 2014
  5. ↑ U.S. Geological Survey, "2016 One-Year Seismic Hazard Forecast for the Central and Eastern United States from Induced and Natural Earthquakes," 2016
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 United States Geological Survey, "Incorporating Induced Seismicity in the 2014 United States National Seismic Hazard Model—Results of 2014 Workshop and Sensitivity Studies," 2015
  7. ↑ U.S. Geological Survey, "The Science of Earthquakes," accessed July 24, 2012
  8. ↑ U.S. Geological Survey, "How Earthquakes Happen," January 11, 2013
  9. ↑ Ballotpedia Energy and Environmental Project Director Kayla Harris, "Interview with Lewis Matthews," July 21, 2015
  10. ↑ 10.0 10.1 U.S. Geological Survey, "Earthquake Glossary - Richter scale," July 18, 2012
  11. ↑ 11.0 11.1 U.S. Geological Survey, "Earthquake Glossary - seismograph," July 18, 2012
  12. ↑ 12.0 12.1 U.S. Geological Survey, "Earthquake Glossary - magnitude," July 18, 2012
  13. ↑ ESG Solutions, "What is Moment Magnitude?" accessed November 15, 2017
  14. ↑ U.S. Geological Survey, "Measuring the Size of an Earthquake," accessed November 16, 2017
  15. ↑ U.S. Geological Survey, "Magnitude / Intensity Comparison," September 29, 2014
  16. ↑ Bulletin of the Seismological Society of America, "Earthquakes Induced by Hydraulic Fracturing in Poland Township, Ohio," January 2015
  17. ↑ Energy In Depth, "Characterization of an Earthquake Sequence Triggered by Hydraulic Fracturing in Harrison County, Ohio," November/December 2014
  18. ↑ Note: This text is quoted verbatim from the original source. Any inconsistencies are attributable to the original source.
  19. ↑ British Columbia Oil and Gas Commission, "Investigation of Observed Seismicity in the Horn River Basin," August 2012
  20. ↑ The Leading Edge, "How did hydraulic-fracturing operations in the Horn River Basin change seismicity patterns in northeastern British Columbia, Canada?" June 2015
  21. ↑ The Leading Edge, "Increased seismicity in Kansas," June 2015
  22. ↑ 22.0 22.1 22.2 22.3 22.4 22.5 22.6 22.7 StatesFirst, "Potential Injection-Induced Seismicity Associated with Oil & Gas Development: A Primer on Technical and Regulatory Considerations Informing Risk Management and Mitigation," accessed February 22, 2017
  23. ↑ Ohio Department of Natural Resources, "Seismic Monitoring," accessed March 1, 2017
  24. ↑ U.S. Geological Survey, "Induced Earthquakes," accessed July 27, 2016
  25. ↑ American Association for the Advancement of Science, "Injection-Induced Earthquakes," July 12, 2013
  26. ↑ U.S. National Academy of Sciences, "Induced Seismicity Potential in Energy Technologies," accessed February 22, 2017
  27. ↑ 27.0 27.1 27.2 27.3 27.4 U.S. Environmental Protection Agency, "Minimizing and Managing Potential Impacts of Injection Induced Seismicity from Class II Disposal Wells: Practical Approaches," February 2015
  28. ↑ LA Times, "Man-made earthquakes increasing in central and eastern U.S., study finds," April 23, 2015
  29. ↑ The New York Times, "U.S. Maps Pinpoint Earthquakes Linked to Quest for Oil and Gas," April 23, 2015
  30. ↑ Seismology Society of America, "Fracking Confirmed as Cause of Rare “Felt” Earthquake in Ohio," January 5, 2015
  31. ↑ Energy in Depth, "Underground Wastewater Disposal," accessed July 9, 2015
  32. ↑ U.S. Environmental Protection Agency, "Class II Oil and Gas Related Injection Wells," accessed November 16, 2017
  33. ↑ 33.0 33.1 33.2 U.S. Environmental Protection Agency, "History of the UIC Program," accessed June 2, 2015
  34. ↑ U.S. Environmental Protection Agency, "History of the UIC Program - Injection Well Time Line," May 4, 2012
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