Underground mining, extractionof fluids and gas from the subsurface, and injection of fluids intounderground formations are clear indicators to the uprising seismicactivities in Oklahoma. Studies have shown wastewater disposalassociated with stimulation and production of oil and gas, which aremajor contributors to recent seismic activities in Oklahoma.This paper reviews the history of oil and gas production, hydraulicfracturing associated with wastewater disposal and their correlationto rising numbers of earthquakes and impending aquifer contaminationin Oklahoma. The paper will also explore the impending areas ofearthquakes and sources of aquifer contamination and examine theprobability of destructive earthquakes on active basement faultssubsequently, recent seismic activities posed little danger to thecommunities. Additionally, the paper will provide an outline ofearthquake and contamination cases in various injection induced areasin Oklahoma, followed by suggested and improvements to wastewaterdisposal.
Injection-Induced Seismicity and Aquifercontamination in Oklahoma
Inducedseismicity is defined as typically minor tremors and earthquakes,which are caused by human activities that alter the strains andstresses in the Earth`s crust. Low magnitude characterizes the mostinduced seismicity. Few sites are a regular to larger quakes, forexample, the California`s geothermal plant. In the past five years,this plant has averaged approximately 15 M3 and M4 events annually.The researcher saves since suggested that majority of largeearthquakes in Oklahoma since the 1930s, for instance, the El Renoearthquake of 1952 with the magnitude of 5.7 is a possible inductionof oil production activities. In Oklahoma State, rates of seismicitysince 2009, according to United States Geological Survey (23),far surpass the previously open rates at any given period during the20th Century. In Oklahoma, oil production has been going on for acentury. Activities related to the production of oil, particularlywastewater disposal in injected wells, are regarded as a potentialcause of earthquakes.
History of Oklahoma`s Oil and GasProduction, Hydraulic Fracturing, Wastewater Disposal, and AquiferContamination
History of Oil and Gas Production
Oil seeps in Oklahoma were recognized inOklahoma before the European settlers arrived, who mined these seepsspecifically for asphalt. It was accidentally recovered in 1869 asthe first subsurface oil near the present-day town of Salina, MayesCounty. The limited amount of oil was sold mainly to be used forlamps. In 1889, the first international oil production came in theform of a well drilled in the form of seeps near Chelsea, RogersCounty. McNamara et al. (2742)documented that the well generated a half-barrel oil sample daily,and was used to get of ticks in cattle as "dip oil."
Oklahoma`s Nellie Johnstone, the firstcommercial well, was drilled in the late 1890s near Bartlesville. Itscompletion came in 1898, which ushered in the Oklahoma territorialoil era. After that, oil production rose rapidly around Oklahomaadding a lot of impetus towards 1907 Statehood granting. The next tenyears saw Oklahoma became the largest entity in the world in the oilproduction (McNamara et al. 2745). Afterthe turn of the 20th Century, some discoveries were made insuccessions in areas around the Oklahoma State, which later encompassas many as what came to be 26 major oil fields.
Oklahoma had three main drilling booms. Thefirst drilling boom occurred immediately after the Statehood.However, it lasted through the 1930s but was most active between 1913and 1920. This spate of drilling resulted in Oklahoma beingconsidered one among leading oil producers. The lull lasted throughthe Second World War and was followed by the second boom, whichreached its peak between 1951 and 1973 (United StatesGeological Survey 67).
According to Fernandez (11),the first drilling boom was led by the size and number of discoveriesthat was made at the onset of the 20th century. The second one was asa result of higher demand for oil and petroleum products during thechange to a peaceful economy. The first two drilling booms were as aresult of world war and economic ages, which had a long-term impacton the oil prices. The third one, which also doubles as the mostrecent, was as a result of increased prices of oil arising from theunsettling political tensions in the Middle East. However, its maincause was a gradual shift in the capacity of the world`s productionreserves and capacity from less-developed countries to consumingcountries represented by OPEC.
In 1967, oil in Oklahoma started a long andtedious downhill production phase with a brief interruption bydrilling booms. The late 1960s saw the state`s capacity of oilproduction maintained by larger, older, and longer-lived oil fields.Hundreds of wells at the time continued to produce, with manyenhanced by the recovery objects involved water injection. Theselarger fields take a longer time to drain, and from recovery enhancedtechniques, which usually continue for many decades.
In that kind of environment, one last majordrilling boom started in the state of Oklahoma. Despite the weakdrilling activity in the area, production of oil arrived at itssecond highest peak in the late 1960s, which saw approximately 231mega-barrels produced (United States Geological Survey 56).A declined started between 1973 and 1976, averaging 6% annually.Oklahoma`s jump in activity was as a result of not only the openingof a geological play but also a rapid rise in the prices of crudeoil, which started in 1974 (Holloway & Oliver 84). The state hadseparated the oil and followed it up by condensation of theproduction since 1976.
Today, the state of Oklahoma ranks 7th in theproduction of oil in the United States and 4th in gas production.William Johnstone and George Keeler are considered Indian Territoryentrepreneurs that opened up the Oklahoma oil and gas boom, whichcontinues to this date. The state`s first commercialized oil well isstill commemorated in the Northern downtown of Bartlesville acrossthe Cherokee Avenue where a replica of the Nellie Johnstone was builton its original site.
Hydraulic Fracturing associated with Wastewater Disposal
Hydraulic fracturing is commonly known as"fracking," is the kind of technology that allows oil andnatural gas recovery from the formation of deep shales within theearth`s crust. For the production of oil and gas, wastewater isgenerated through operations associated with drilling and production.When oil or gas wells are hydraulically fractured, millions of watergallons (along with additives and sands), are pumped into rocksbearing hydrocarbons formed deep into the earth. Rodgers (25)noted that some of this water is permanently locked in the formation.However, some will emerge through the wells to the earth surface, andis known as "blowback."
In hydraulic fracturing, the liquid is pumpedinto the shale, which in turn causes fissures allowing oil and gascontained in the same shale be released. This process, according toUnited States Geological Survey (101),was first used close to six decades ago. In Oklahoma for instance,this technology has a long history. Hydraulic fracturing was firstimplemented commercially in 1949, east of Stephens and DuncanCounties. The technology behind it was allowed to be used in Oklahomamainly to increase oil production.
Hydraulic fracturing, according to Xie(57), is associated with wastewater disposalbut is not the same thing. For instance, technology that is hydraulicfracturing involves well stimulation process that enhances the flowof oil or gas from a well. On the other hand, wastewater disposalconsiders the wastewater injection into the designated well but ismuch deeper. The association is as a result of the hydrocarbonbearing typical formations containing a lot of water, which is knownas "produced water" when pumped to the earth`s surface withoil or gas.
The last few decades have seen an increase inthe number of fracking (hydraulic fracturing) shale oil and naturalgas wells in the United States, and specifically in Oklahoma. Shaleformation alone located in Oklahoma is home to thousands of hydraulicfracturing wellheads. Advancement in technology over the years hasseen vast oil and gas reserves, which makes it reachable,commercially. However, as more "fracking" wells began itsoperations, so does the pressure on the surface and ground watersupplies, as a result of water used to facilitate the process, andthus needing up to over a million gallons of water for every wellheadto complete the process of hydraulic fracturing.
Of importance in this process is the continualgrowth of wastewater that is generated from the hydraulic frackingwells, which requires recycling or disposal. According to UnitedKuwayama (22), over 61% of water injected intothe wells, in Oklahoma for instance, during the "fracking"process will result in a discharge shortly after that, and is termedas "flow back wastewater." Since water is the main fluidand larger component used in the hydraulic fracturing, its essentialsremain an important factor in the economics and operation of oil andgas collection. In Oklahoma, the recent times have seen wastewaterand fresh water procedural operations, which have been in use sincethe late 1980s, are experiencing strict regulations in governmentbased on disposal limitations and water availability.
Water that is used in the process of hydraulicfracturing is usually disposed of and managed in one of the threewas:
Injected into permitted disposal wellheads in relations with the Underground Injection Control (UIC) regulations.
Delivered to the water treatment facilities, and
In Oklahoma, disposal options depend on somefactors, which includes the availability of favorable injectionzones, that is the capacity of commercial or municipal facilities forwater treatment. Again, it is based on the ability of the plants oroperators to obtain water discharge permits successfully. But howdoes hydraulic fracturing process associated with wastewater disposalcorrelates with the rising number of earthquakes in Oklahoma? And howhave it impact on the impending aquifer contamination in Oklahoma?
Correlation with Rising Number of Earthquakes in Oklahoma
In recent years, scientists and researchershave been studying a possible correlation between wastewaterdisposals as a result of hydraulic fracturing process to seismicityin Oklahoma. In the 1990s for instance, scientists had determined amore definitely correlation than others, with other credible expertsnoting that seismicity risk due to hydraulic fracturing associatedwith wastewater disposal is high. Cheremisinoff et al. (41)says that of the 45,000 disposal wells used for the production of oiland gas wastewater, "a huge fraction of this wastewater disposalhave induced seismic waves and earthquakes, and is a concern to thegeneral public."
However, there are other parties, for instance,the National Research Council in the United States, have sincediscredited the correlation in noting that "on a fraction"of wastewater injected activities linked to seismicity. The NationalResearch Council once stated that,
"Thousands of wastewater disposalwellheads have existed in the United States to dispose of thesewaters generated by oil and gas production and geothermal operations,which includes shale gas production. Water injection into the wellsfor disposal is suspected or determines to be a likely cause forartificially-induced seismicity at just ten sites over severaldecades ago" (United States Geological Survey 144).
In recent years, much focus has been in thestate of Oklahoma characterized by thousands of wastewater disposalhead wells. A geologist in Oklahoma once cautioned that "nosingle seismograph station before the 1970s existed," and thatthere are 20 in recent times, which suggest critical observationsabout the increased seismic activities because, partly due toimproved detection technology. "Because oil and natural gas areproduced in 69 of 77 Oklahoma counties, and any of the seismicactivities is likely to occur near the crude oil and gas activity"(United States Geological Survey 140).
In a new research on 19th June 2015 publishedin the Journal of Science Advances, Mark Zobach, a Stanford Professorand another doctorate student, Rall Walsh, showed that "Oklahoma`srising seismic activities and some earthquakes coincide withincreasing salt wastewater disposal into the Arbuckle formation"(Uddameri et al. 65). This is a 6,000-foot-deep formation ofsediments in the state of Oklahoma. Additionally, the primary sourceof the wastewater triggering earthquake is not the "flow backwater," which is generated by the hydraulic fracturing process,but "produced water," commonly referred to as brackishwater coexisting between oil and natural gas within the Earth`scrust.
This correlation means that hydraulicfracturing does not cause the majority of the induced earthquakes inOklahoma, but wastewater disposal. Of importance about increasedearthquakes is the growing wastewater volumes generated from thehydraulically-fractured wells, which required recycling or disposal.What the induced wastewater does to the drilling infrastructure.According to United States Geological Survey (145),it is plausible that the seismic tremors are likely to affect theintegrity of the wells. It is important to note that thousands ofdisposal wells exist in Oklahoma, and the majority of them aresuspected to have induced seismic activities since the late 1960s.
Correlation with Impending Aquifer Contamination in Oklahoma
About the environmental crisis in Oklahoma, itsresidents have in recent times expressed concerns about the qualityof drinking water, which is pumped from the underground aquifers.These concerns have since forwarded to the relevant authorities tostop the link between hydraulic fracturing (fracturing) and groundwater contamination. The state inspection to ascertain thiscorrelation showed that the state`s groundwater tests attest toincreasing levels of chlorides, methane, and the hazardous chemicalbenzene, which according to McNamara et al. (2744), may cause cancer.Since the water wells and aquifers lying below the state are alsofound to be heavily contaminated with the fracking-related chemicalsubstances, the responsible authorities believed that it is apotential ticking time bomb.
The basis for such correlation is from thefindings by the United States Patent Office, which indicated that:
"Hydraulic fracturing results in hugewastewater quantities, whereby these fracking fluids are injectedartificially into the wells containing chemicals that can be adverseor toxic to humans and animals. These chemicals include chemicalsknown to trigger cancer-causing cells. A substance such as dieselfuels contain benzene, toluene, xylene, and ethylbenzene, and areregarded as carcinogenic at limited concentrations" according tothe United States 8,158,097 patent number (McNamara 2744).
However, the United States and the state ofOklahoma officials have been quicker to deny any possible orcorrelation between hydraulic fracturing and aquifer contaminationand the connection to seismicity.
Despite this evident refusal of environmentalquality of aquifers by the state delegations, Oklahoma is consideredto home to one of the best natural resources globally. For instance,the state boasts of the Ogallala Aquifer, which is the largestaquifer in the entire world. Approximately 82 percent of the Midwestresidents, which include a larger section of Oklahoma State, usewater for consumption, including drinking, from the vast OgallalaAquifer. Despite this revelation, the Oklahoma Congress, according tothe revelations, had commissioned a rigorous research study onwhether the hydraulic fracturing associated with wastewater disposalis environmentally not favorable to the quality of underground water.The EPA even went forward to release a four-year study draft, and asection of stated that it "did not find any evidence linking themechanism of hydraulic fracturing and wastewater disposal to thewidespread and systemic impact on the drinking water aquifers in theUnited States" (United States Geological Survey 138).This also includes Oklahoma`s largest aquifer, Ogallala.
However, such a study by the relevantauthorities could not discredit the fact that hydraulic-fracturedwaste water disposal shows particular instances where the processcontaminate clean drinking water natural resources (aquifers),including water wells. Further, a 2014 peer-reviewed study concludedthat aquifers and drinking water wells near the hydraulic fracturingsites in Oklahoma were contaminated with "ethane and methanethat had chemical substances, including gases. This normally arefound deep into the underground," According to UnitedStates Geological Survey (89) added thatdrilling using the process of hydraulic fracturing has "contaminatedaquifers through wastewater and chemical spills, poor integrity ofwells and other ways."
This prevalence of aquifer contamination inOklahoma is evidenced by the City of Norman and other municipalitiesin the metropolitan that draws water from Oklahoma`s Central Aquifer.This aquifer underlies approximately 3,000 square miles in Oklahomaand other states around. It is commonly referred to as theWellington-Garber aquifer since the large quantities of water are inthe Wellington Permian age formation and Garber Sandstone. These rockunits emerged because of the ancient discontinuity of river system,sandstones (interbedded channel bars), and floodplain deposits(Kuwayama 23).
Here, the complexity of stratigraphy of theaquifer generates a complicated groundwater system, and, in turn,promotes the interaction of chemicals with rocks and water. Thewestern section of the state`s aquifer is buried or confined to thePermian age group. This translates to the fact that the drinkingwater in the buried section of the aquifer is more removed from theprecipitation recharge than the section of the waters exposed by theunburied section. Therefore, the effects due to chemical interactionsand contamination between rock and water become more prevalent.
Impending areas of earthquakes and sourcesof aquifer contamination
In recent times, Oklahoma State hasexperienced not so usual large numbers of earthquakes. The shakesrise at the same time production of oil and gas are intensified inthe area. The United States Geological Survey (USGS) studied morethan 3,000 Oklahoma earthquakes in recent times to ascertain theexact areas in the state and the unknown correlation with the faults.
Approximately 1,800 impending areas ofearthquakes in Oklahoma have since been identified as the majority ofthem having moment magnitudes greater than or are equal to 3.5, 65other earthquakes with magnitudes exceeding 4.0 and a fear otherareas recording over 5.0 magnitudes. By the end of 2017, the OklahomaState will record earthquakes magnitude of 3.0 across potentialareas. Bakshi (78) observed that theOklahoma State is seismically active by a substantial margin,especially the northern areas towards the city of Kansas. With theinduced seismicity prevalent in the state, it is projected that bythe end of 2019, will very likely increase in number. This is becausewastewater in disposal wells has triggered the majority ofearthquakes in the state in recent times, especially in the centraland south-central of Oklahoma.
Sources of aquifer contamination in Oklahomaare large as a result of small amounts of arsenic concentrations. Ofimportance is the fact that these arsenic concentrations naturallyoccurs in almost all the rocks making up the aquifer. However, someareas within the state show increased amounts of concentrations(almost 10 µg/L) in aquifer waters. In Norman aquifer, for example,232 µg/L was measured in the confined sections. Other areas of theaquifers are characterized by arsenic concentrations, which occur inOklahoma`s western regions. According to United StatesGeological Survey (47), the Normal Cityofficials saw the potential contamination of aquifer waters andstopped carrying out drilling process in the entire section of thecity.
The conditions and processes that resulted inincreased levels of arsenic concentrations as the main contaminantsof aquifer waters, especially the Central Oklahoma aquifer, areclearly understood. Much of this understanding about aquifercontamination arose from the United States Quality Water Assessmentprogram (Cheremisinoff et al. 45). Theprogram had carried out its operations since the 1980s to determinethe composition of rocks, movement of groundwater, and waterchemistry in the aquifers underlying the state.
The study showed that the groundwater towards the southwesternregion of the Oklahoma`s Central Aquifer is pushed by apotentiometric highly-centered southwest Oklahoma County. In Normanarea, for example, flow-paths travel towards the southern parts ofthe state through the county of Cleveland, which eventuallydischarges into the river drainage system. Other travels to the westdescend under the confine units before navigating through theCounty`s eastern parts (United States Geological Survey 140).Of importance to note is that these flow-paths are deeper, slower,and longer so that these waters spend much more times in contact withthe aquifer contents.
In the aquifers like the Central OklahomaAquifer and Norman Aquifer, the release of arsenic concentrations toground water occurs when the pH exceeds 8.4 standard units. Thedominances in which the geochemical process causes an increase in thepH were the dissolution of and cation exchanges of Dolomites. Alongthe long flow paths that characterize the confined parts of Oklahomaaquifers, experiences elevated process that the pH nears neutrality(7.0) to over 8.5. At this point, the arsenic concentrations start todesorb from the aquifer mineral grains and remains in aquifer waters.
However, contamination of aquifers inOklahoma by arsenic concentrations and other geochemical materialstend to increase its levels with an increase in depth. The majorityof private wells in the state of Oklahoma draw water from shallowsections of the aquifer, which is approximately close to 300 feetbelow the earth surface. Shallow wellheads rarely produce clean waterexceeding the MCL (Uddameri et al. 67).Therefore, arsenic concentration and other materials do notsignificantly affect domestic use and irrigation activities. Normanmunicipal wells in Oklahoma that are approximately 500 to 800 feetdeep, either draws water from the deep buried or deep unburiedaquifer systems.
Oklahoma`s Active Basement Faults, DestructiveEarthquakes, and Seismic Activities
The majority of Oklahoma`s active basementfaults are perfectly aligned and naturally measured to slip underpressure, which is submitted through faraway tectonic plates makingup the continent`s boundaries. The state`s confined rock layers aresqueezed towards the east-west section of the Atlantic ridge, Juan deFuca Ridge, and San Andreas Fault.
These basement faults in the state are beingawakened by the drilling of oil and gas through the injection offluids into the deep-lying underground rocks above the active layersmaking up the faults (Xie 67). Thesefluids reduce the amount of pressure on the active faults, and onceit has had enough force for the underlying rocks to break apart, ittriggers earthquakes. Some of the faults unknown previously threatenthe critical Oklahoma oil and gas infrastructure, for example, theprivately-owned facilities in Cushing. One of the active faults liesdirectly below Cushing airport, which means is a probable cause ofthe earthquake.
Destructive earthquakes in Oklahoma are as aresult of the huge escalation of the state`s seismicity. Looking atthe larger scale across the United States, over 3000 wastewaterdisposal have triggered damaging earthquakes (McNamara et al.2748). The increase in water pressures hascoincided with the Oklahoma City`s earthquakes clusters.Water-induced seismicity and earthquakes start below the Earth`ssurface, whereby the wastewater increases the fluid pressures on thefaults, and thus makes it easy for the slipping process, and thetremors resulted in destructive earthquakes.
However, Oklahoma`s recent seismic activitieshave posed little danger to the communities. The reason for this isOklahoma State taking serious measures on carrying out saferinjection wells. Here, seismic studies are paid close attentionbefore the wells are built and wastewater injection is carried out.This way, the authorities involved can monitor the earthquakepossibilities to be in a better position to identify thepossibilities and shut down dangerous wells that are at risk oftriggering seismic waves and earthquakes.
Earthquakes and contamination cases in Oklahomaare as a result of more than 3,500 active injection-induced areas.These contaminated areas are also earthquake-prone and arecharacterized by underlying injection-induced wellheads. Three mainareas in Oklahoma are Perry, Cherokee, and Jones. These areas,according to Holloway & Oliver (89), have experienced the largestnumber of earthquake and contamination cases in recent years. Theseareas are characterized by increasing quakes and water contaminationfollowing the processes of wastewater disposal. The total amount ofinjected wastewater wells, and at the same time, the total size ofhydraulic fracturing concludes that the injected water andcontamination cases in these areas applied conventional techniques ofoil extraction.
Solutions to Improvement of WastewaterDisposal
Considering the sources of the Oklahoma`srecent quakes are known, regulators and scientists have sinceproposed a possible solution to wastewater disposal. One possiblesolution would be to stop, entirely, the injection of produced waterinto the formation of Arbuckle (Rodgers 27). Instead, the injectionshould be carried out back, for example, into the producingformations of an oil-rich limestone rock layers where a lot of theproduced water in the state of Oklahoma originates from.
Another solution would be to establish acentralized approach to wastewater treatment and reuse.Centralization process not only provides flow back wastewatertreatment and reuse from some of the largest numbers of wellheads inOklahoma whenever the wells undergo hydraulic fracturing, but alsoprovides produced wastewater treatment and reuse for the long-term,which means full lifecycle.
Furthermore, a more centralized system wouldprovide the much-needed solution considering it can easily access andtake advantage of alternative sources of water, for example, as fromthe municipal wastewater equipment, which would have otherwise beenunlikely to be acquired (United States Geological Survey 145).Additionally, wellheads that provide shale oil and production of gasare considered long-term processes, which would exceed two decadesterm. However, conventional solutions should be brought in play tohandle fresh sources of water, which will be geared towards theshort-term.
Again another solution to wastewater disposalshould be impounded through evaporation in trucking and surface waterto deep well injection sites over a long distance. Treating flow backwastewaters to be reused at the wellheads are all targeted at theshort-term, but its positive effects will be able to address othercritical issues on the long-term (Schultz 34).These long-term solutions will be able to handle issues such asdiminished sources of water as a result of wastewater disposal,contamination, and improved water resources.
In Oklahoma, the rise in seismicity is as aresult of subsurface fluids and natural gas extraction, mining, andthe injection of fluids into the underground formations. Theprocesses have since led to cases of earthquakes, seismic activities,contamination of wellheads following complete wastewater disposal.Wastewater disposal is largely associated with hydraulic fracturing,which is a technological process involving oil and natural gasrecovery due to the formation of deep shales within the crust.
The paper, therefore, focused on Oklahoma`shistory in the production of oil and gas and hydraulic fracturingassociated with wastewater disposal. The correlation was identifiedto have resulted in a high number of earthquakes in Oklahoma. Thecorrelation was also identified to be one of the reasons for inducedseismicity. Again, the paper touched on aquifer contamination and itsassociation with hydraulic fracturing. Finally, Oklahoma`s activebasement faults were noted to be one of the main reasons for a highnumber of destructive earthquake and seismic activities reported inthe area. This, in turn, contributes to aquifer contamination due tothe presence of geochemical materials in the rocks. Improvement ofwastewater disposal is also studied in the paper.
Bakshi, Vivek. Shale Gas: A Practitioner`s Guide to Shale Gas &Other Unconventional Resources. London, United Kingdom: Globe Lawand Business, 2012. Print.http://jwelb.oxfordjournals.org/content/7/1/63.extract
Cheremisinoff, Nicholas P, Anton Davletshin, and M Dayal. HydraulicFracturing Operations: Handbook of Environmental ManagementPractices. , 2015. Internet resource.https://books.google.co.ke/books/about/Hydraulic_Fracturing_Operations.html?id=JwNhBgAAQBAJ&redir_esc=y
Holloway, Michael D, and Oliver Rudd. Fracking: The Operations andEnvironmental Consequences of Hydraulic Fracturing. Salem, Mass:Scrivener Publishing/Wiley, 2013. Print.http://eu.wiley.com/WileyCDA/WileyTitle/productCd-1118496329.html
Kuwayama, Yusuke, Sheila Olmstead, and Alan Krupnick. "WaterQuality and Quantity Impacts of Hydraulic Fracturing." CurrentSustainable/renewable Energy Reports. 2.1 (2015): 17-24. Print.http://link.springer.com/article/10.1007%2Fs40518-014-0023-4#/page-1
McNamara, D E, H M. Benz, R B. Herrmann, E A. Bergman, P Earle, AHolland, R Baldwin, and A Gassner. "Earthquake Hypocenters andFocal Mechanisms in Central Oklahoma Reveal a Complex System ofReactivated Subsurface Strike-Slip Faulting." GeophysicalResearch Letters. 42.8 (2015): 2742-2749. Print. Retrieved fromhttp://onlinelibrary.wiley.com/doi/10.1002/2014GL062730/full
Rogers, S M. History of Litigation Concerning Hydraulic Fracturingto Produce Coalbed Methane: Leaf and the Hydraulic FracturingDecisions. Oklahoma City: Interstate Oil and Gas CompactCommission, 2009. Internet resourcehttp://iogcc.publishpath.com/Websites/iogcc/Images/Marvin%20Rogers%20Paper%20of%20History%20of%20LEAF%20Case%20Jan.%202009.pdf
Schultz, Aarik. Hydraulic Fracturing and Natural Gas Drilling:Questions and Concerns. , 2012. Internet resourcehttps://books.google.co.ke/books/about/Hydraulic_Fracturing_and_Natural_Gas_Dri.html?id=ySCKZwEACAAJ&redir_esc=y
Uddameri, Venkatesh, Audra Morse, and Kay J. Tindle. HydraulicFracturing Impacts and Technologies: A Multidisciplinary Perspective,2015. Internet resource.https://books.google.co.ke/books/about/Hydraulic_Fracturing_Impacts_and_Technol.html?id=bVUErgEACAAJ&redir_esc=y
United States Geological Survey. United States Earthquakes.Golden, Colo: U.S. Dept. of the Interior, Geological Survey, 2006.Print. Retrieved fromhttps://books.google.com.au/books/about/United_States_Earthquakes.html?id=GzUJAAAAIAAJ
Xie, Furen. Rock Stress and Earthquakes. Hoboken: CRC Press,2010. Internet resource.https://books.google.co.ke/books/about/Rock_Stress_and_Earthquakes.html?id=sk7CbwAACAAJ&redir_esc=y