Induced seismicity is typically minor
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
s and tremors that are caused by
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
activity that alters the stresses and strains on
Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
. Most induced seismicity is of a low
magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
. A few sites regularly have larger quakes, such as
The Geysers
The Geysers is the world's largest geothermal field, containing a complex of 18 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains approximately north of San Francisco, California.
Geysers produce ...
geothermal plant in California which averaged two M4 events and 15 M3 events every year from 2004 to 2009.
The Human-Induced Earthquake Database (''HiQuake'') documents all reported cases of induced seismicity proposed on scientific grounds and is the most complete compilation of its kind.
Results of ongoing multi-year research on induced earthquakes by the
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
(USGS) published in 2015 suggested that most of the significant earthquakes in Oklahoma, such as the 1952 magnitude 5.7 El Reno earthquake may have been induced by deep injection of waste water by the oil industry. A huge number of seismic events in fracking states like Oklahoma caused by increasing the volume of injection. "Earthquake rates have recently increased markedly in multiple areas of the Central and Eastern United States (CEUS), especially since 2010, and scientific studies have linked the majority of this increased activity to wastewater injection in deep disposal wells."
[via EBSCO]
Induced seismicity can also be caused by the injection of carbon dioxide as the storage step of carbon capture and storage, which aims to sequester carbon dioxide captured from fossil fuel production or other sources in Earth's crust as a means of climate change mitigation. This effect has been observed in Oklahoma and Saskatchewan.
Though safe practices and existing technologies can be utilized to reduce the risk of induced seismicity due to injection of carbon dioxide, the risk is still significant if the storage is large in scale. The consequences of the induced seismicity could disrupt preexisting faults in the Earth's crust as well as compromise the seal integrity of the storage locations.
The
seismic hazard
A seismic hazard is the probability that an earthquake will occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold. With a hazard thus estimated, risk can be assessed and includ ...
from induced seismicity can be assessed using similar techniques as for natural seismicity, although accounting for non-stationary seismicity.
It appears that earthquake shaking from induced earthquakes is similar to that observed in natural tectonic earthquakes, although differences in the depth of the rupture need to be taken into account. This means that
ground-motion models derived from recordings of natural earthquakes, which are often more numerous in strong-motion databases than data from induced earthquakes, can be used. Subsequently, a risk assessment can be performed, taking account of the seismic hazard and the
vulnerability
Vulnerability refers to "the quality or state of being exposed to the possibility of being attacked or harmed, either physically or emotionally."
A window of vulnerability (WOV) is a time frame within which defensive measures are diminished, com ...
of the exposed elements at risk (e.g. local population and the building stock). Finally, the risk can, theoretically at least, be mitigated, either through modifications to the hazard or a reduction to the exposure or the vulnerability.
Causes
![Fluids and faults](https://upload.wikimedia.org/wikipedia/commons/3/35/Fluids_and_faults.jpg)
There are many ways in which induced seismicity has been seen to occur. In the 2010s, some energy technologies that inject or extract fluid from the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
, such as oil and gas extraction and geothermal energy development, have been found or suspected to cause seismic events. Some energy technologies also produce wastes that may be managed through disposal or storage by injection deep into the ground. For example, waste water from oil and gas production and
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
from a variety of industrial processes may be managed through underground injection.
Artificial lakes
The column of water in a large and deep
artificial lake
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
alters in-situ stress along an existing fault or fracture. In these reservoirs, the weight of the water column can significantly change the stress on an underlying fault or fracture by increasing the total stress through direct loading, or decreasing the effective stress through the increased pore water pressure. This significant change in stress can lead to sudden movement along the fault or fracture, resulting in an earthquake. Reservoir-induced seismic events can be relatively large compared to other forms of induced seismicity. Though understanding of reservoir-induced seismic activity is very limited, it has been noted that seismicity appears to occur on dams with heights larger than . The extra water pressure created by large reservoirs is the most accepted explanation for the seismic activity. When the reservoirs are filled or drained, induced seismicity can occur immediately or with a small time lag.
The first case of reservoir-induced seismicity occurred in 1932 in Algeria's
Oued Fodda Dam.
![Koyna-Dam](https://upload.wikimedia.org/wikipedia/commons/2/2d/Koyna-Dam.jpg)
The 6.3 magnitude
1967 Koynanagar earthquake
The 1967 Koynanagar earthquake occurred near Koynanagar town in Maharashtra, India on 11 December local time. The magnitude 6.6 shock hit with a maximum Mercalli intensity of VIII (''Severe''). It occurred near the site of Koyna dam, raising qu ...
occurred in
Maharashtra
Maharashtra (; , abbr. MH or Maha) is a states and union territories of India, state in the western India, western peninsular region of India occupying a substantial portion of the Deccan Plateau. Maharashtra is the List of states and union te ...
,
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
with its
epicenter
The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates.
Surface damage
Before the instrumental pe ...
,
fore- and
aftershock
In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...
s all located near or under the
Koyna Dam reservoir
The Koyna Dam is one of the largest dams in Maharashtra, India. It is a rubble-concrete dam constructed on Koyna River which rises in Mahabaleshwar, a hillstation in Sahyadri ranges. It is located in Koyna Nagar, Satara district, in the Wes ...
. 180 people died and 1,500 were left injured. The effects of the earthquake were felt away in Bombay with tremors and power outages.
During the beginnings of the
Vajont Dam
The Vajont Dam (or Vaiont Dam) is a disused dam in northern Italy. It is one of the tallest dams in the world, with a height of . It is in the valley of the Vajont River under Monte Toc, in the municipality of Erto e Casso, north of Venice.
...
in Italy, there were seismic shocks recorded during its initial fill. After a landslide almost filled the reservoir in 1963, causing a massive flooding and around 2,000 deaths, it was drained and consequently seismic activity was almost non-existent.
On August 1, 1975, a magnitude 6.1 earthquake at
Oroville,
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, was attributed to seismicity from a large earth-fill
dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
and
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
recently constructed and filled.
The filling of the
Katse Dam
The Katse Dam, a concrete arch dam on the Malibamat'so River in Lesotho, is Africa's second largest double-curvature arch dam. (The Tekezé Dam, completed in early 2009, is now Africa's largest double curvature dam). The dam is part of the Lesot ...
in
Lesotho
Lesotho ( ), officially the Kingdom of Lesotho, is a country landlocked country, landlocked as an Enclave and exclave, enclave in South Africa. It is situated in the Maloti Mountains and contains the Thabana Ntlenyana, highest mountains in Sou ...
, and the
Nurek Dam
The Nurek Dam (russian: Нурекская ГЭС; Tajik: Нерӯгоҳи обии Норак, ''Nerūgohi obii Norak'', Tajik for Nurek Hydro-electric Station) is an earth-fill embankment dam on the Vakhsh River in Tajikistan. Its primary purp ...
in
Tajikistan
Tajikistan (, ; tg, Тоҷикистон, Tojikiston; russian: Таджикистан, Tadzhikistan), officially the Republic of Tajikistan ( tg, Ҷумҳурии Тоҷикистон, Jumhurii Tojikiston), is a landlocked country in Centr ...
is an example. In
Zambia
Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most cent ...
,
Kariba Lake may have provoked similar effects.
The
2008 Sichuan earthquake, which caused approximately 68,000 deaths, is another possible example. An article in
''Science'' suggested that the construction and filling of the
Zipingpu Dam
Zipingpu Dam (紫坪铺水利枢纽) is an embankment dam on the Min River near the city of Dujiangyan, Sichuan Province in southwest China. It consists of four generators with a total generating capacity of 760 MW. Construction began in 2001 a ...
may have triggered the earthquake.
Some experts worry that the
Three Gorges Dam
The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has been the world ...
in
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
may cause an increase in the frequency and intensity of earthquakes.
Mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
affects the
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
state of the surrounding rock mass, often causing observable
deformation
Deformation can refer to:
* Deformation (engineering), changes in an object's shape or form due to the application of a force or forces.
** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies.
* Defor ...
and
seismic activity
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
. A small portion of mining-induced events are associated with damage to mine workings and pose a risk to mine workers.
These events are known as
rock burst
A rock burst is a spontaneous, violent failure of rock that can occur in high-stress mines. Although mines may experience many mining-related seismic events, only the tremors associated with damage to accessible mine workings are classified as ro ...
s in
hard rock mining
Underground hard-rock mining refers to various underground mining techniques used to excavate "hard" minerals, usually those containing metals, such as ore containing gold, silver, iron, copper, zinc, nickel, tin, and lead. It also involves the ...
, or as
bumps
A bumps race is a form of rowing race in which a number of boats chase each other in single file, each crew attempting to catch and ‘bump’ the boat in front without being caught by the boat behind.
The form is mainly used in intercollegia ...
in
underground coal mining
Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...
. A mine's propensity to burst or bump depends primarily on depth, mining method, extraction sequence and geometry, and the material properties of the surrounding rock. Many underground hardrock mines operate seismic monitoring networks in order to manage bursting risks, and guide mining practices.
Seismic networks have recorded a variety of mining-related seismic sources including:
* Shear slip events (similar to
tectonic earthquakes) which are thought to have been triggered by mining activity. Notable examples include the 1980 Bełchatów earthquake and the
2014 Orkney earthquake.
* Implosional events associated with mine collapses. The
2007 Crandall Canyon mine collapse and the Solvay Mine Collapse are examples of these.
* Explosions associated with routine mining practices, such as
drilling and blasting
Drilling and blasting is the controlled use of explosives and other methods, such as gas pressure blasting pyrotechnics, to break rock for excavation. It is practiced most often in mining, quarrying and civil engineering such as dam, tunnel o ...
, and unintended explosions such as the
Sago mine Disaster
The Sago Mine disaster was a coal mine explosion on January 2, 2006, at the Sago Mine in Sago, West Virginia, United States, near the Upshur County seat of Buckhannon. The blast and collapse trapped 13 miners for nearly two days; only one su ...
. Explosions are generally not considered "induced" events since they are caused entirely by chemical payloads. Most earthquake monitoring agencies take careful measures to identify explosions and exclude them from earthquake catalogs.
*
Fracture formation near the surface of excavations, which are usually small magnitude events only detected by dense in-mine networks.
*
Slope failures, the largest example being the
Bingham Canyon Landslide.
Waste disposal wells
![Cumulative induced seismicity](https://upload.wikimedia.org/wikipedia/commons/7/79/Cumulative_induced_seismicity.png)
Injecting liquids into waste disposal wells, most commonly in disposing of
produced water
Produced water is a term used in the oil industry or geothermal industry to describe water that is produced as a byproduct during the extraction of Petroleum, oil and natural gas, or used as a medium for heat extraction. Produced water is the kind ...
from oil and natural gas wells, has been known to cause earthquakes. This high-saline water is usually pumped into salt water disposal (SWD) wells. The resulting increase in subsurface pore pressure can trigger movement along faults, resulting in earthquakes.
One of the first known examples was from the
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 completed December 1942, operated by the United States Army throughout the late ...
, northeast of
Denver
Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
. In 1961, waste water was injected into deep strata, and this was later found to have caused a series of earthquakes.
The
2011 Oklahoma earthquake
The 2011 Oklahoma earthquake was a 5.7 magnitude intraplate earthquake which occurred near Prague, Oklahoma on November 5 at 10:53 p.m. CDT (03:53 UTC November 6) in the U.S. state of Oklahoma. The epicenter of the ear ...
near
Prague
Prague ( ; cs, Praha ; german: Prag, ; la, Praga) is the capital and largest city in the Czech Republic, and the historical capital of Bohemia. On the Vltava river, Prague is home to about 1.3 million people. The city has a temperate ...
, of magnitude 5.8, occurred after 20 years of injecting waste water into porous deep formations at increasing pressures and saturation.
On September 3, 2016, an even stronger earthquake with a magnitude of 5.8 occurred near
Pawnee, Oklahoma
Pawnee (Pawnee: Paári, iow, Páñi Chína) is a city and county seat of Pawnee County, Oklahoma, United States. The town is northeast of Stillwater at the junction of U.S. Route 64 and State Highway 18.
It was named for the Pawnee tribe, wh ...
, followed by nine aftershocks between magnitudes 2.6 and 3.6 within hours. Tremors were felt as far away as
Memphis, Tennessee
Memphis is a city in the U.S. state of Tennessee. It is the seat of Shelby County in the southwest part of the state; it is situated along the Mississippi River. With a population of 633,104 at the 2020 U.S. census, Memphis is the second-mos ...
, and
Gilbert, Arizona
Gilbert is a town in Maricopa County, Arizona, United States, located southeast of Phoenix within the city's metropolitan area. Incorporated on July 6, 1920, Gilbert was once known as the "Hay Shipping Capital of the World". It is the fifth-larg ...
.
Mary Fallin
Mary Fallin (; née Copeland; born December 9, 1954) is an American politician who served as the 27th governor of Oklahoma from 2011 to 2019. A member of the Republican Party, she was elected in 2010 and reelected in 2014. She was the first and s ...
, the Oklahoma governor, declared a local emergency and shutdown orders for local disposal wells were ordered by the Oklahoma Corporation Commission. Results of ongoing multi-year research on induced earthquakes by the
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
(USGS) published in 2015 suggested that most of the significant earthquakes in Oklahoma, such as the 1952 magnitude 5.5 El Reno earthquake may have been induced by deep injection of waste water by the oil industry.
Prior to April 2015 however, the Oklahoma Geological Survey's position was that the quake was most likely due to natural causes and was not triggered by waste injection. This was
one of many earthquakes which have affected the Oklahoma region.
Since 2009, earthquakes have become hundreds of times more common in Oklahoma with magnitude 3 events increasing from 1 or 2 per year to 1 or 2 per day. On April 21, 2015, the Oklahoma Geological Survey released a statement reversing its stance on induced earthquakes in Oklahoma: "The OGS considers it very likely that the majority of recent earthquakes, particularly those in central and north-central Oklahoma, are triggered by the injection of produced water in disposal wells."
Hydrocarbon extraction and storage
Large-scale fossil fuel extraction can generate earthquakes. Induced seismicity can be also related to underground gas storage operations. The 2013 September–October seismic sequence occurred 21 km off the coast of the Valencia Gulf (Spain) is probably the best known case of induced seismicity related to Underground Gas Storage operations (the Castor Project). In September 2013, after the injection operations started, the Spanish seismic network recorded a sudden increase of seismicity. More than 1,000 events with magnitudes () between 0.7 and 4.3 (the largest earthquake ever associated with gas storage operations) and located close the injection platform were recorded in about 40 days. Due to the significant population concern the Spanish Government halted the operations. By the end of 2014, the Spanish government definitively terminated the concession of the UGS plant. Since January 2015 about 20 people who took part in the transaction and approval of the Castor Project were indicted.
Groundwater extraction
The changes in crustal stress patterns caused by the large scale extraction of groundwater has been shown to trigger earthquakes, as in the case of the
2011 Lorca earthquake.
Geothermal energy
Enhanced geothermal systems
An enhanced geothermal system (EGS) generates geothermal electricity without the need for natural convective hydrothermal resources. Until recently, geothermal power systems have exploited only resources where naturally occurring heat, water, and ...
(EGS), a new type of
geothermal power
Geothermal power is electrical power generated from geothermal energy. Technologies in use include dry steam power stations, flash steam power stations and binary cycle power stations. Geothermal electricity generation is currently used in 2 ...
technology that does not require natural convective hydrothermal resources, are known to be associated with induced seismicity. EGS involves pumping fluids at pressure to enhance or create permeability through the use of hydraulic fracturing techniques. Hot dry rock (HDR) EGS actively creates geothermal resources through hydraulic stimulation. Depending on the rock properties, and on injection pressures and fluid volume, the reservoir rock may respond with tensile failure, as is common in the oil and gas industry, or with shear failure of the rock's existing joint set, as is thought to be the main mechanism of reservoir growth in EGS efforts.
HDR and EGS systems are currently being developed and tested in Soultz-sous-Forêts (France), Desert Peak and
the Geysers
The Geysers is the world's largest geothermal field, containing a complex of 18 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains approximately north of San Francisco, California.
Geysers produce ...
(U.S.), Landau (Germany), and Paralana and Cooper Basin (Australia). Induced seismicity events at the Geysers geothermal field in California has been strongly correlated with injection data. The test site at Basel, Switzerland, has been shut down due to induced seismic events. In November 2017 a Mw 5.5 struck the city of Pohang (South Korea) injuring several people and causing extensive damage. The proximity of the seismic sequence to an EGS site, where stimulation operations had taken place only a few months before the earthquake, raised the possibility that this earthquake had been anthropogenic. According to two different studies it seems plausible that the
Pohang earthquake was induced by EGS operations.
Researchers at MIT believe that seismicity associated with hydraulic stimulation can be mitigated and controlled through predictive siting and other techniques. With appropriate management, the number and magnitude of induced seismic events can be decreased, significantly reducing the probability of a damaging seismic event.
Induced seismicity in Basel Induced seismicity in Basel led to suspension of its hot dry rock enhanced geothermal systems project. A seismic-hazard evaluation was then conducted, resulting in the cancellation of the project in December 2009. Basel, Switzerland sits atop a hist ...
led to suspension of its HDR project. A seismic hazard evaluation was then conducted, which resulted in the cancellation of the project in December 2009.
Hydraulic fracturing
Hydraulic fracturing
Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "frack ...
is a technique in which high-pressure fluid is injected into the low-permeable reservoir rocks in order to induce fractures to increase
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
production. This process is generally associated with
seismic events that are too small to be felt at the surface (with moment
magnitudes ranging from −3 to 1), although larger magnitude events are not excluded. For example, several cases of larger magnitude events (M > 4) have been recorded in Canada in the unconventional resources of
Alberta
Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
and
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
.
Carbon capture and storage
Risk analysis
Operation of technologies involving long-term geologic storage of waste fluids have been shown to induce seismic activity in nearby areas, and correlation of periods of seismic dormancy with minima in injection volumes and pressures has even been demonstrated for fracking wastewater injection in Youngstown, Ohio. Of particular concern to the viability of carbon dioxide storage from coal-fired power plants and similar endeavors is that the scale of intended CCS projects is much larger in both injection rate and total injection volume than any current or past operation that has already been shown to induce seismicity. As such, extensive modeling must be done of future injection sites in order to assess the risk potential of CCS operations, particularly in relation to the effect of long-term carbon dioxide storage on shale caprock integrity, as the potential for fluid leaks to the surface might be quite high for moderate earthquakes.
However, the potential of CCS to induce large earthquakes and CO
2 leakage remains a controversial issue.,
Monitoring
Since geological
sequestration of carbon dioxide has the potential to induce seismicity, researchers have developed methods to monitor and model the risk of injection-induced seismicity in order to manage better the risks associated with this phenomenon. Monitoring can be conducted with measurements from an instrument such as a
geophone
A geophone is a device that converts ground movement (velocity) into voltage, which may be recorded at a recording station. The deviation of this measured voltage from the base line is called the seismic response and is analyzed for structure of ...
to measure the movement of the ground. Generally a network of instruments is used around the site of injection, although many current carbon dioxide injection sites use no monitoring devices. Modelling is an important technique for assessing the potential for induced seismicity and two primary models are used: Physical and numerical. A physical model uses measurements from the early stages of a project to forecast how the project will behave once more carbon dioxide is injected. A numerical model, on the other hand, uses numerical methods to simulate the physics of what is happening within the reservoir. Both modelling and monitoring are useful tools whereby to quantify, understand better and mitigate the risks associated with injection-induced seismicity.
Failure mechanisms due to fluid injection
To assess induced seismicity risks associated with carbon storage, one must understand the mechanisms behind rock failure. The
Mohr-Coulomb failure criteria describe shear failure on a fault plane. Most generally, failure will happen on existing faults due to several mechanisms: an increase in shear stress, a decrease in normal stress or a
pore pressure
Pore water pressure (sometimes abbreviated to pwp) refers to the pressure of groundwater held within a soil or rock, in gaps between particles ( pores). Pore water pressures below the phreatic level of the groundwater are measured with piezometer ...
increase.
The injection of supercritical will change the stresses in the reservoir as it expands, causing potential failure on nearby faults. Injection of fluids also increases the pore pressures in the reservoir, triggering slip on existing rock weakness planes. The latter is the most common cause of induced seismicity due to fluid injection.
The Mohr-Coulomb failure criteria state that
with
the critical
shear stress
Shear stress, often denoted by (Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. ''Normal stress'', on the ot ...
leading to failure on a fault,
the
cohesive strength along the fault,
the normal stress,
the friction coefficient on the fault plane and
the pore pressure within the fault.
When
is attained, shear failure occurs and an earthquake can be felt. This process can be represented graphically on a
Mohr's circle
Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor.
Mohr's circle is often used in calculations relating to mechanical engineering for materials' strength, geotechnical engineer ...
.
Comparison of risks due to CCS versus other injection methods
While there is risk of induced seismicity associated with
carbon capture and storage
Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
underground on a large scale, it is currently a much less serious risk than other injections. Wastewater injection, hydraulic fracturing, and secondary recovery after oil extraction have all contributed significantly more to induced seismic events than carbon capture and storage in the last several years. There have actually not been any major seismic events associated with carbon injection at this point, whereas there have been recorded seismic occurrences caused by the other injection methods. One such example is massively increased induced seismicity in Oklahoma, USA caused by injection of huge volumes of wastewater into the Arbuckle Group sedimentary rock.
Electromagnetic pulses
It has been shown that high-energy
electromagnetic pulse
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic fie ...
s can trigger the release of energy stored by tectonic movements by increasing the rate of local earthquakes, within 2–6 days after the emission by the EMP generators. The energy released is approximately six orders of magnitude larger than the EM pulses energy. The release of tectonic stress by these relatively small triggered earthquakes equals to 1-17% of the stress released by a strong earthquake in the area. It has been proposed that strong EM impacts could control seismicity as during the periods of the experiments and long time after, the seismicity dynamics were a lot more regular than usual.
Risk analysis
Risk factors
Risk is defined as the chance/probability of being exposed to hazard. The hazard from earthquakes depends on proximity to potential earthquake sources, their magnitudes, and rates of occurrence and is usually expressed in probabilistic terms. Earthquake hazards can include ground shaking, liquefaction, surface fault displacement, landslides, tsunamis, and uplift/subsidence for very large events (M
L > 6.0). Because induced seismic events, in general, are smaller than M
L 5.0 with short durations, the primary concern is ground shaking.
Ground shaking
Ground shaking can result in both structural and nonstructural damage
to buildings and other structures. It is commonly accepted that structural damage to modern engineered structures happens only in earthquakes larger than M
L 5.0. The main parameters in structural damage is
peak ground velocity
In seismology, strong ground motion is the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forci ...
(PGV). Ground shaking is usually measured as
peak ground acceleration
Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an wikt:accelerogram, accelerogram at a ...
(PGA) in
seismology
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
and
earthquake engineering
Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earth ...
. When PGA is greater than 18-34% of g (the force of gravity), moderate structural damage is possible, and very strong shaking can be perceived. In rare cases, nonstructural damage
has been reported in earthquakes as small as M
L 3.0. For critical facilities like dams and nuclear plants, it is crucial to ensure the ground shaking is not able to cause any unaffordable damages.
Human anxiety
Human anxiety is another factor in determining the risk of induced seismicity. Anxiety refers to the human concern created by low-level ground shaking. Because injection-induced seismicity is generally of a small magnitude and short duration, human anxiety is often the only or primary hazard associated with felt events.
Probabilistic seismic hazard analysis
''Extended reading
An Introduction to Probabilistic Seismic Hazard Analysis (PSHA)'
Probabilistic Seismic Hazard Analysis (PSHA) is aimed to quantify the possibility of the ground motion reaching certain arbitrary levels or thresholds at a site when taking all the possible earthquakes (both natural and induced) into consideration.
It is used for building codes in both United States and Canada, as well as protecting dams and nuclear plants from the damage of seismic events.
Major inputs
= Source zone characterization
=
Understanding the geological background on the site is a prerequisite for seismic hazard analysis. Parameters that contribute to possible seismic events should be understood before the analysis. Formations of the rocks, subsurface structures, locations of faults, state of stresses and other parameters that contribute to possible seismic events are considered. Records of past earthquakes of the site are also required.
= Recurrence pattern
=
The magnitudes of all earthquakes that occurred at the studied site can be utilized in the
Gutenberg-Richter relation, as shown below,
where
is the magnitude of seismic events,
is the number of events with magnitudes bigger than
,
is the rate parameter and
is the slope.
and
vary at different sites. By studying the catalogs of previous earthquakes,
and
for one specific site can be interpreted, hence the number (probability) of earthquakes exceeding a certain magnitude can be predicted.
= Ground motion
=
Ground motion consists of amplitude, frequency and duration of the shaking.
PGV (peak ground velocity) and
PGA (peak ground acceleration) are often used in describing ground motion. By combining PGV and PGA parameters with
Modified Mercalli intensity
The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...
(MMI) for a certain site,
ground motion potential equations can be utilized to estimate the ground motions related to induced seismic events, particularly at close distances.
Methodology
The standard PSHA uses the distributions of different inputs to generate various models for prediction. Another way is to combine
Monte-Carlo simulation
Monte Carlo methods, or Monte Carlo experiments, are a broad class of computational algorithms that rely on repeated random sampling to obtain numerical results. The underlying concept is to use randomness to solve problems that might be determini ...
in PSHA.
By considering all the parameters, as well as the uncertainties in these parameters, seismic hazards of the interested sites can be described statistically.
Output
In the end, PSHA is able to give an estimation of the potential damages from induced seismicity in both magnitudes and distances. In the analysis, damage thresholds can be set by MMI, PGA or PGV. Probabilistic hazard analyses indicate that hazards cannot be mitigated effectively within 5 km, that is to say, no operations should be performed (an exclusion zone) within 5 km of the site.
It is also suggested that real-time monitoring and immediate response protocol be required within 25 km from the site.
Mitigation
Induced seismicity can cause damage to infrastructure and can also lead to brine and leakages.
It is easier to predict and mitigate seismicity caused by explosions. Common mitigation strategies include constraining the amount of dynamite used in one single explosion and the locations of the explosions. For injection-related induced seismicity, however, it is still difficult to predict when and where induced seismic events will occur, as well as the magnitudes. Because induced seismic events related to fluid injection are unpredictable, it has garnered more attention from the public. Induced seismicity is only part of the chain reaction from industrial activities that worry the public. Impressions toward induced seismicity are very different between different groups of people.
The public tends to feel more negatively towards earthquakes caused by human activities than natural earthquakes.
Two major parts of public concern are related to the damages to infrastructure and the well-being of humans.
Most induced seismic events are below M 2 and are not able to cause any physical damage. Nevertheless, when the seismic events are felt and cause damages or injuries, questions arise from the public whether it is appropriate to conduct oil and gas operations in those areas. Public perceptions may vary based on the population and tolerance of local people. For example, in the seismically active Geysers geothermal area in Northern California, which is a rural area with a relatively small population, the local population tolerates earthquakes up to M 4.5. Actions have been taken by regulators, industry and researchers. On October 6, 2015, people from industry, government, academia, and the public gathered together to discuss how effective it was to implement a traffic light system or protocol in Canada to help manage risks from induced seismicity.
Traffic Light System
To mitigate the possible consequences of induced seismicity, hazard and risk assessment is essential. A Traffic Light System (TLS), also referred to as Traffic Light Protocol (TLP), is a calibrated control system served as a direct mitigation method for induced seismicity. Its merits consist of providing continuous and real-time monitoring and management of ground shaking of induced seismicity for specific sites. TLS was first implemented in 2005 in an enhanced geothermal plant in Central America. For oil and gas operations, the most widely implemented one is modified by the system used in the UK. Normally there are two types of TLS – the first one sets different thresholds, usually earthquake local magnitudes (ML) or ground motion (PGV) from small to large. If the induced seismicity reaches the smaller thresholds, modifications of the operations should be implemented by the operators themselves and the regulators should be informed. If the induced seismicity reaches the larger thresholds, operations should be shut down immediately. The second type of traffic light system sets only one threshold. If this threshold is reached, the operations are halted. This is also called a "stop light system". Thresholds for the traffic light system vary between and within countries, depending on the area. Risk assessment and tolerance for induced seismicity, however, is subjective and shaped by different factors like politics, economics, and understanding from the public.
Nuclear explosions
Nuclear explosions can cause seismic activity, but according to USGS, the resulting seismic activity is less energetic than the original nuclear blast, and generally does not produce large aftershocks. Nuclear explosions may instead release the
elastic strain energy that was stored in the rock, strengthening the initial blast
shockwave.
U.S. National Research Council report
A 2013 report from the
U.S. National Research Council examined the potential for energy technologies—including shale gas recovery, carbon capture and storage, geothermal energy production, and conventional oil and gas development—to cause earthquakes.
[U.S. National Research Council Report, Induced Seismicity Potential in Energy Technologies, https://www.nap.edu/catalog/13355/induced-seismicity-potential-in-energy-technologies] The report found that only a very small fraction of injection and extraction activities among the hundreds of thousands of energy development sites in the United States have induced seismicity at levels noticeable to the public. However, although scientists understand the general mechanisms that induce seismic events, they are unable to accurately predict the magnitude or occurrence of these earthquakes due to insufficient information about the natural rock systems and a lack of validated predictive models at specific energy development sites.
Induced Seismicity Potential in Energy Technologies
The report noted that hydraulic fracturing has a low risk for inducing earthquakes that can be felt by people, but underground injection of wastewater produced by hydraulic fracturing and other energy technologies has a higher risk of causing such earthquakes. In addition, carbon capture and storage—a technology for storing excess carbon dioxide underground—may have the potential for inducing seismic events, because significant volumes of fluids are injected underground over long periods of time.
List of induced seismic events
Table
References
Further reading
*
*
* {{cite journal , last1=Foulger , first1=G.R. , last2=Wilson , first2=M.P. , last3=Gluyas , first3=J.G. , last4=Julian , first4=B.R. , last5=Davies , first5=R.J. , title=Global review of human-induced earthquakes , journal=Earth-Science Reviews , date=2018 , volume=178 , pages=438–514 , doi=10.1016/j.earscirev.2017.07.008 , bibcode=2018ESRv..178..438F , doi-access=free
External links
The Human-Induced Earthquake DatabaseMap of reservoir-induced earthquakesat International Rivers
WEBINAR: Yes, Humans Really Are Causing Earthquakes–
IRIS Consortium
IRIS (Incorporated Research Institutions for Seismology) is a university research consortium dedicated to exploring the Earth's interior through the collection and distribution of seismographic data. IRIS programs contribute to scholarly research, ...
One-year seismic hazard forecast for the Central and Eastern United States from induced and natural earthquakes–
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
, 2016 (with maps)
Induced Earthquakes–
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
website
Seismology