the potential for induced seismicity in energy technologies

Pa s s i v e s e i s m i c a n d m i c r o s e i s m i c — Pa r t 2

1438 The Leading Edge December 2012

SPECIAL SECTION: Pa s s i v e s e i s m i c a n d m i c r o s e i s m i c — Pa r t 2

The potential for induced seismicity in energy technologies

The great majority of earthquakes that occur each year around the world have natural causes. A small number of

lesser-magnitude seismic events have been related to human activities and are called “induced seismic events” or “induced earthquakes” (NRC, 2012). Of concern are induced events that are large enough to be noticed by the public, typically events larger than magnitude 3 (note the range earthquake sizes that are felt can widely vary depending on project location and site characteristics). Induced seismic activity has been described since at least the 1920s and attributed to various human activities including the impoundment of water reservoirs, controlled explosions related to mining and construction, underground nuclear tests, and energy technology developments that involve injection or withdrawal of fluids from the subsurface. Historically known induced seismicity has generally been small in both magnitude and intensity of ground shaking.

In the United States, several induced seismic events in the past few years related to energy technology development proj-ects have heightened public attention although none of these events resulted in loss of life or significant structural damage (Figure 1). Nonetheless, these induced seismic events, though small in scale, can be disturbing to the public, especially in areas where natural (tectonic) seismic events are rare, and raise concern about induced seismic activity and its potential consequences.

An ad-hoc committee (see author list) of the National Re-search Council (NRS) of the National Academies was asked to examine the scale, scope, and consequences of seismicity induced during fluid injection and withdrawal related to geo-thermal energy development, oil and gas development includ-ing shale gas recovery, and carbon capture and storage (CCS).

JULIE E. SHEMETA, MEQ GeoELIZABETH A. EIDE, National Research CouncilMURRAY W. HITZMAN, Colorado School of MinesDONALD D. CLARKE, Geological ConsultantEMMANUEL DETOURNAY, University of Minnesota, CSIROJAMES H. DIETERICH, University of California, RiversideDAVID K. DILLON, David K. Dillon PE, LLC

The work of the committee resulted in a report that was pub-lished in June 2012 (http://www.nap.edu/catalog.php?record_id=13355). This article reviews the significant points of the report specifically related to oil and gas production, includ-ing disposal of wastewater. Note that some researchers (e.g., McGarr et al., 2002) draw a distinction between “induced” seismicity and “triggered” seismicity. Under this distinction, induced seismicity results from human-caused stress changes in the Earth’s crust that are on the same order as the ambient stress on a fault that causes slip. Triggered seismicity results from stress changes that are a small fraction of the ambient stress on a fault that causes slip. Thus, anthropogenic process-es could potentially “trigger” large and potentially damaging earthquakes, but anthropogenic processes cannot “induce” such events. In this article, we do not distinguish between the two and use the term induced seismicity to cover both categories.

A significant contribution to the study’s results derived from compilation of a database of published information on historical events that were either confirmed or suspected to be related to human activity (Figure 1). This study also took place during a period in which a number of small, felt seismic events occurred that were caused by or were likely related to fluid injection for energy development (for example, seismic-ity in 2011 and 2012 potentially associated with a wastewater disposal well in Youngstown, Ohio). Because of their recent occurrence, peer-reviewed publications about most of these events were not available. However, knowing that these events and information about them would be anticipated in their re-port, the committee attempted to identify information from as many credible sources as possible to gain a sense of the common factual points involved in each instance, as well as the remaining, unanswered questions about these cases. In a number of these recent cases, as well as some of the events for which published information exists, identifying the cause of a seismic event as directly related to one or another form of energy technology development is ambiguous. The study attempted to distinguish between those events that were con-firmed to be related to injection or withdrawal of fluid related to energy development and those where the causal mecha-nisms were not entirely confirmed.

Causes of induced seismicityFaults can, in principle, be activated if the shear stress (τ) acting on the fault overcomes its shear resistance. In most cases, the shear resistance (or shear strength) is caused by friction. The shear strength is proportional to the difference

SIDNEY J. GREEN, University of UtahROBERT M. HABIGER, SpectraseisROBIN K. MCGUIRE, Lettis Consultants InternationalJAMES K. MITCHELL, Virginia Polytechnic Institute and State UniversityJOHN L. (BILL) SMITH, Geothermal ConsultantJASON R. ORTEGO, University of CaliforniaCOURTNEY R. GIBBS, National Research Council

Editor’s note: Anticipating public concern about the potential for ener-gy development projects to induce seismicity, the U.S. Congress directed the U.S. Department of Energy to request that the National Research Council assemble an ad-hoc committee of experts to examine seismic-ity induced during fluid injection and withdrawal activities related to energy technologies. In addition to the scale, scope, and consequences and steps toward best practices, the study was also to identify gaps in knowledge and research needed to advance the understanding of induced seismicity; identify gaps in induced seismic hazard assessment methodologies and the research to close those gaps, and to assess options for steps toward best practices with regard to continued energy develop-ment and minimizing induced seismicity potential. The committee, which served pro bono, conducted its work for about 14 months. The major results of the report, published in June 2012, are discussed in this article. The complete report also provides information on the study process and information collected.

December 2012 The Leading Edge 1439


between the normal stress (σ) act-ing on the fault, and the pressure (p) of the fluid permeating the fault and the surrounding rock. The fault remains stable as long as the magnitude of the shear stress (τ) is smaller than the frictional strength, represented by this expression: μ(σ – p). The term (σ – p) is the effective stress and μ is the friction coefficient. This condition for triggering slip is the Coulomb criterion and the key parameters controlling the ini-tiation of slip are thus the normal and shear stresses acting on the fault, which in turn is effected by the pore fluid pressure (or pore pressure).

Although the conditions for initiating slip on a pre-existing fault are well understood, it is dif-ficult to make reliable estimates of the various quantities in the Coulomb criterion. Lacking these estimates, predicting how close or how far a fault system is from instability remains problematic, even if the orientation of the fault is known. This implies that the magnitude of the increase in pore pressure that will cause a known fault to slip cannot generally be calculated. Nonetheless, a large body of evidence suggests that the state of stress and pore pressure are often not far from the critical conditions throughout much of the crust (Zoback and Zoback, 1980, 1989), and therefore a small de-stabilizing perturbation of the stress and/or of the pore pres-sure could cause a critically oriented fault to slip.

Injection or extraction of fluid into or from a permeable rock induces not only a pore-pressure change in the reservoir, but also a perturbation in the stress field in the reservoir and in the surrounding rock. The physical mechanism responsible for this hydraulically induced stress perturbation can be illus-trated by considering the injection of a finite volume of fluid inside a porous elastic sphere surrounded by a large imperme-able elastic body (Figure 2). The magnitude of the induced pore pressure (Δp), once equilibrated, is proportional to the volume of fluid injected. An analysis of the pore pressure and stress perturbation indicates that, in general, fluid injection increases the risk of slip along a fault in the region where the pore pressure has increased. In the case of fluid withdrawal, the region at risk is generally outside the reservoir (see also Nicholson and Wesson, 1990).

The magnitude of the induced pore-pressure increase and the extent of the region of pore-pressure change depend on the rate of fluid injection and total volume injected, as well as the rock’s intrinsic permeability (k), its storage coefficient (S), and on the fluid viscosity (μ). This difference manifests itself

Figure 1. Sites in the United States and Canada with documented reports of seismicity caused by or potentially related to energy development from various energy technologies. The reporting of the occurrence of small induced seismic events is limited by the detection and location thresholds of seismic monitoring networks (NRC, 2012).

Figure 2. (a) Injection of a finite volume of fluid inside the porous elastic sphere embedded in a large impermeable elastic body induces a pore-pressure increase p inside the sphere as well as a stress perturbation inside and outside the sphere, caused by the expansion ΔV of the sphere. (b) If the sphere is freed from its elastic surrounding, it will expand by the amount ΔV* caused by the pore pressure increase Δp. (c) A confining stress Δσ* needs to be applied on the free sphere to prevent the expansion ΔV* caused by Δp. If the material in the surrounding medium is much softer than the material in the sphere, then ΔV ΔV* and Δσ 0; if the medium is much stiffer, then ΔV 0 and Δσ Δσ* . (Δσ* refers only to the radial stress at the interface between the porous sphere and the impermeable medium.)



when comparing relatively impermeable crystalline rocks and more permeable rocks such as sedimentary units. Faults and fractures in crystalline rocks offer relatively little resistance to flow, and thus the equivalent permeability and diffusivity of these fractured rocks (with fractures and rocks viewed as a whole) can be high. The combination of high transmissivity, small storativity, and the planar nature of fractures implies that significant pore-pressure changes can be transmitted over considerable distances (several kilometers) through a fracture network from an injection well. In contrast, in permeable rocks, where the fluid is dominantly transported by a con-nected network of pores, the injection of fluid from a well can be viewed as giving rise to an expanding “bulb”, centered on the well, which represents the region where the pore pressure has increased. The increase in pore pressure decreases with increasing distance from the well to zero at the edge of this expanding region.

The region of perturbed pore pressure continues to grow radially until it meets bulbs growing from other injection wells or until it reaches the lateral boundaries of the reservoir (see also Nicholson and Wesson, 1990).

Considerations for oil and gas projectsInducing a significant seismic event requires both an in-crease or decrease of the pore pressure relative to the pore pressure that existed prior to fluid injection or withdrawal, and that this change in pore pressure occur over a region large enough to encompass a fault area where the fault can undergo movement caused by the new fluid pressure exceed-ing its critical state of stress. We briefly examine oil and gas

extraction (fluid withdrawal), waterflooding for enhanced recovery, and hydraulic fracturing projects in terms of their potential to cause induced seismic events. Among the tens of thousands of wells used for carbon dioxide (CO2) flooding for enhanced recovery in the United States, the study did not find any documentation in the published literature of felt induced seismicity and this technology is not addressed further in this article.

Oil and gas extraction. Withdrawal of oil and gas has been linked to felt seismic events at 38 sites globally, 20 of which were in the United States (Figure 1). These events in the Unit-ed States have occurred in Texas, Oklahoma, California, Lou-isiana, Illinois, and Nebraska, and the majority have been of M < 4.0. Outside the United States well-documented signifi-cant events have occurred at the Lacq gas field in southwest-ern France (largest magnitude 4.2) (Grasso and Wittlinger 1990; Segall et al., 1994) and the Gazli gas field in Uzbekistan where events up to magnitude 7 have been recorded (Adush-kin et al., 2000; Grasso, 1992; Simpson and Leith, 1985). At Gazli, the locations and magnitudes of these earthquakes were determined from worldwide seismograph data, leading to some uncertainty on the causal relationship between gas extraction and earthquake activity. However, observations of crustal uplift and the proximity of the earthquakes to the Ga-zli gas field, which is in a previously seismically quiet region, suggest that they were induced by hydrocarbon extraction.

These extraction events are rare relative to the large num-ber of oil and gas fields in the United States (Table 1) and globally. Withdrawal of oil or gas from the subsurface can lead to a net decrease in pore pressure in the reservoir over

Energytechnology

Number of projects

Number offelt-induced events

Maximummagnitudeof felt event

Numberof events M > 4.0 c

Net reservoirpressure change

Mechanismfor inducedseismicity

Secondary oil and gas recovery (waterflooding)

~108,000 (wells) One or more felt events at 18 sites across thecountry

4.9 3 Attempt tomaintain balance

Pore pressureincrease

Tertiary oil and gas recovery (EOR)

~13,000 None known None known 0 Attempt tomaintain balance

Pore pressure increase (likely mechanism)

Hydraulic fracturing for shale gas production

~35,000 wells total 1 2.8 0 Initial positive; then withdraw

Pore pressureincrease

Hydrocarbon with-drawal

~6,000 fields 20 sites 6.5 5 Withdrawal Pore pressuredecrease

Wastewaterdisposal wells

~30,000 8 4.8 b 7 Addition Pore pressureincrease

Table 1. Historical summary information about felt-induced seismic caused by or likely related to energy technology development a in the United States.a Note that that in several cases the causal relationship between the technology and the event was suspected but not confirmed. Determining whether a particular earthquake was caused by human activity is often difficult. The references for the events in Table 1 and the way in which causality may be determined are discussed in the NAS report. Also important is the fact that the well numbers are those wells in operation today, while the numbers of events listed extend over a total period of decades. Table 1 summarizes data available to the authors through 2010.b M 4.8 is a moment magnitude. Earlier studies reported magnitudes up to M 5.3 on an unspecified scale; those magnitudes were derived from local instruments.c Although seismic events M > 2.0 can be felt by some people in the vicinity of the event, events M > 4.0 can be felt by most people and may be accompanied by more significant ground shaking, potentially causing greater public concern.



time especially if fluids are not re-injected to maintain or re-turn to original pore pressure conditions. This change in pore pressure can cause changes in the state of stress of the sur-rounding rock mass and of nearby faults with the potential to result in induced seismic events.

Waterflooding for enhanced recovery. Approximately 108,000 wells are currently permitted in the United States for waterflooding for enhanced recovery. This does not in-clude wells that have been used for waterflooding and have either been shut-in or have been used for other purposes such as CO2 flooding. Few historical or current wells have been as-sociated with felt induced seismic events (Table 1). Operators on waterflooding projects generally do not exceed preproduc-tion pore pressure, attempting instead to maintain relative balance between the volumes of fluid injected and extracted. Exceptions to this general case have included waterflooding at the Rangely Field in Colorado, where induced seismic events occurred with magnitudes up to M 3.4 (Gibbs et al., 1973) and seismic events near Snyder, Texas where magnitudes as large as M 4.6 occurred after the initiation of a large water-flooding project in Cogdell Field (Nicholson and Wesson, 1990).

Hydraulic fracturing for unconventional oil and gas de-velopment. Extraction of gas and oil from unconventional reservoirs has been made feasible through the combined application of horizontal drilling and multistage hydraulic fracturing. Estimates suggest that more than ~35,000 wells drilled for unconventional oil and gas development exist in the United States today (EPA, 2011). Microseismicity (M < 2) during hydraulic fracture injection is a well-established tool for estimating hydraulic fracture geometry. Felt seismic-ity associated with hydraulic fracturing is rare with only one documented case worldwide (Blackpool, England) in which hydraulic fracturing was confirmed as the cause of felt seismic events (Eisner et al., 2011). Three other possible earthquake sequences in Oklahoma have been discussed in the literature that may be associated with hydraulic fracturing (Nicholson and Wesson, 1990; Holland, 2011). In the most recent case, in 2011, hydraulic fracturing was cited as the possible cause of felt induced seismic events, the largest of which was M 2.8 (Holland, 2011). Despite the fact that hydraulic fractur-ing does increase pore pressure above the minimum in situ stress (typically σh), the area affected by the increase in pore pressure is generally small, remaining in the near vicinity of the created fracture. Felt-induced seismic activity would be expected only if this small area of increased pore pressure in-tersected a fault of sufficient size and near critical conditions of stress.

Wastewater disposal wells. Wastewater originates from oil and gas production or flowback following hydraulic frac-turing. Tens of thousands of wastewater disposal wells are currently active throughout the country. Most wastewater disposal wells typically involve injection at relatively low pres-sures into large porous aquifers that have high natural perme-ability, specifically targeted to accommodate large volumes of fluid. Although only a few felt-induced seismic events have been directly linked to these disposal wells (Table 1), a few

incidences have occurred recently, generating considerable public attention. Examination of seismic activity in both the Dallas-Fort Worth area of Texas (Frohlich et al., 2010; Frohlich, 2012) and Guy-Greenbrier area of Arkansas (Hor-ton, 2012) has suggested causal links between the injection zones and subsurface faults that were not previously recog-nized as providing the potential for induced seismic activity. Seismicity may be triggered by fluid injection in the presence of a nearby fault which has the suitable combination of ori-entation, properties, and state of stress.

SummaryMany wells are currently permitted in the United States for a combination of hydrocarbon extraction, secondary recovery, tertiary recover, hydraulic fracturing and wastewater dispos-al; however, only a few documented incidents have occurred where the injection caused or was likely related to felt seismic events. The factor that appears to have the most direct con-sequence in regard to induced seismicity is the net fluid bal-ance (total balance of fluid introduced into or removed from the subsurface), although additional factors may influence the way fluids affect the subsurface. Factors which are im-portant in the relationship between energy technologies and induced seismicity include: the depth, rate and net volume of injected or extracted fluids, bottom-hole pressure, perme-ability of the relevant geologic layers, locations and proper-ties of faults, and crustal stress conditions. While the general mechanisms that create induced seismic events are well un-derstood, we are currently unable to accurately predict the magnitude or occurrence of such events caused by the lack of comprehensive data on complex natural rock systems and the lack of validated predictive models.

Protocols for assessing and dealing with induced seismic-ity have been developed, such as the U.S. Department of En-ergy protocol for addressing induced seismicity associated with Enhanced Geothermal Systems (EGS) (Majer, et al., 2012). Induced seismicity protocols designed for specific injection programs such as wastewater wells and hydraulic fracturing could be developed and used as a guide for the many issues associated with induced seismicity, such as site characteriza-tion, seismic monitoring, and public awareness and safety. The NRC study recommended that protocols for oil and gas development should be considered, using the protocols devel-oped for ESG as a general guideline. A “traffic light” control system within a protocol can be established to respond to an instance of induced seismicity, allowing for low levels of seis-micity but adding monitoring and mitigation requirements if induced seismic events increase in magnitude or frequency.

The key findings and research recommendations resulting from the NRC study are summarized below.

General1) Only a small fraction of injection and extraction activities

among the hundreds of thousands of energy development wells in the United States have induced seismicity at levels that are noticeable to the public.

2) Current models employed to understand the predictability

December 2012 The Leading Edge 1443


of the size and location of earthquakes in response to net fluid injection or withdrawal require calibration from field observations. The success of these models has not yet been evaluated, in large part caused by the lack of basic data at most locations on the interactions among rock, faults, and fluid as a complex system.

3) Injection pressures and net fluid volumes in energy tech-nologies, such oil and gas production, are generally con-trolled to avoid increasing pore pressure in the reservoir above the initial reservoir pore pressure. These technolo-gies thus appear less problematic in terms of inducing felt seismic events than technologies that result in a significant net increase or decrease in net fluid volume.

4) Existing regional seismic arrays may not be capable of pre-cisely locating small induced seismic events to determine causality and better establish the characteristics of induced seismicity.

5) Temporary local seismic arrays can be installed to find faults, determine source mechanisms, decrease error in lo-cation of seismic events, and increase spatial resolution of future events.

6) Injected fluid volume, injection rate, injection pressure, and proximity to existing faults and fractures are factors that determine the probability of creating a seismic event. High injection volumes in the absence of corresponding extractions may increase pore pressure and, in proximity to existing faults, could lead to an induced seismic event.

7) The area of potential influence from injection wells may extend over several square miles and induced seismicity may continue for months to years after injection ceases.

8) Reducing the injection volumes, rates, and pressures have been successful in decreasing rates of felt seismicity in cases where events have been induced.

Oil and gas1) Generally, withdrawal associated with conventional oil

and gas recovery has not caused significant seismic events; however, several major earthquakes have been associated with conventional oil and gas withdrawal.

2) Relative to the large number of waterflood projects for secondary recovery, the small number of documented in-stances of felt induced seismicity suggests such projects pose relatively small risk for events that would be of con-cern to the public.

3) The committee did not identify any documented, felt in-duced seismic events associated with EOR (tertiary recov-ery).

4) The process of hydraulic fracturing a well as presently im-plemented for shale gas recovery does not pose a high risk for inducing felt seismic events. About 35,000 wells have been hydraulically fractured for shale gas development to date in the United States. One case of induced seismicity (maximum M 1.9) was documented in Oklahoma in the late 1970s as being caused by hydraulic fracturing for oil and gas development for conventional oil and gas extrac-tion.

Wastewater disposal1) The United States currently has approximately 30,000

Class II wastewater disposal wells; few felt induced seismic events have been reported as either caused by or likely re-lated to these wells. Rare cases of wastewater injection have produced seismic events, and these were typically less than M 5.0.

2) Evaluating the potential for induced seismicity in the loca-tion and design of injection wells is difficult because no cost-effective way to locate unmapped faults and measure in situ stress currently exists.

Research recommendationsDespite ongoing induced seismicity in areas around the coun-try, few high-quality induced earthquake data sets exist. The regional networks are typically too sparse to provide accurate hypocentral position estimates near potentially troublesome wells, creating difficultly in establishing a direct cause and effect relationship. One of the NRC report research recom-mendations pertains to the need for high-quality data col-lection in both the field and laboratory. Guidelines for data collection would be defined in the prospective oil and gas in-duced seismicity protocol. In addition to getting good data, researching methods to collect in situ stress measurements in a nondestructive manner was also highlighted as an im-portant issue. Another key research concern is understand-ing the occurrence of microseisms within natural fracture systems and the effect of temperature variations on stressed jointed rock systems. The fracture /temperature relationship has immediate relevance to geothermal energy projects and may have potential benefit to other energy technologies. In addition, research on the relationship between injection rate, pressure, and event size was identified as an important re-search area.

Modeling recommendations made in the NRC report in-clude identifying ways in which simulation models could be scaled appropriately to make the required predictions of field observations. The currently available and new geomechanical and earthquake simulation models could be used to identify the most critical geological characteristics, fluid injection or withdrawal parameters, and rock and fault properties control-ling induced seismicity. Focused research should be imple-mented to advance development of linked geomechanical and earthquake simulation models that could be utilized to bet-ter understand potential induced seismicity—and relate this understanding to the occurrence and size of seismic events. Modeling to further develop simulation capabilities that inte-grate existing reservoir modeling capabilities with earthquake simulation modeling is important for hazard and risk assess-ment. These models can be refined on a probabilistic basis as more data and observations are gathered and analyzed. Finally, continued development of coupled reservoir fluid flow and geomechanical simulation codes, used currently in geothermal fields, could be used to understand the processes underlying the occurrence of seismicity after wells have been shut in.



ReferencesAdushkin, V. V., V. N. Rodionov, S. Turuntnev, and A. E. Yodin,

2000, Seismicity in the oil Field: Oilfield Review, Summer, 2–17.Eisner, L., E. Janská, I. Opršal, and P. Matoušek, 2011, Seismic analy-

sis of the events in the vicinity of the Preese Hall well: Report from Seismik to Cuadrilla Resources.

Frohlich, C., E. Potter, C. Hayward, and B. Stump, 2010, Dallas-Fort Worth earthquakes coincident with activity associated with natu-ral gas production: The Leading Edge, 29, no. 3, 270–275, http://dx.doi.org/10.1190/1.3353720.

Frohlich, C., 2012, Two-year survey comparing earthquake activity and injection-well locations in the Barnett Shale, Texas: PNAS.

Gibbs, J. F., J. H. Healey, C. B. Raleigh, and J. Coakley, 1973, Seis-micity in the Rangley, Colorado, area, 1962–1970: Bulletin of the Seismological Society of America, 63, no. 5, 1557–1570.

Grasso, J.-R. and Wittlinger. 1990, 10 years of seismic monitoring over a gas field area: Bulletin of the Seismological Society of Amer-ica, 80, 450–473.

Grasso, J.-R., 1992, Mechanics of seismic instabilities induced by the recovery of hydrocarbons: Pure and Applied Geophysics, 139, no. 3–4, 506–534, http://dx.doi.org/10.1007/BF00879949.

Holland, A., 2011, Examination of possibly induced seismicity from hydraulic fracturing in the Eola Field, Garvin County, Oklahoma: Oklahoma Geological Survey Open-File Report OF1-2011.

Horton, S., 2012, Disposal of hydrofracking waste fluid by injection into subsurface aquifers triggers earthquake swarm in central Ar-kansas with potential for damaging earthquake: Seismological Research Letters, 83, no. 2, 250–260, http://dx.doi.org/10.1785/gssrl.83.2.250.

Majer, E., J. Nelson, A. Robertson-Tait, J. Savy, and I. Wong, 2012, Protocol for addressing induced seismicity associated with en-hanced geothermal systems: U.S. Department of Energy.

McGarr, A., 1991, On a possible connection between three major earthquakes in California and oil production: Bulletin of the Seis-mological Society of America, 81, no. 3, 948–970.

McGarr, A., D. Simpson, and L. Seeber, 2002, Case histories of in-duced and triggered seismicity in W.H.K Lee, H. Kanamori, P.C. Jennings, and C. Kisslinger, eds., International handbook of earthquake and engineering seismology, Part A: Academic Press, 647–661.

Nicholson, C. and R. L. Wesson, 1990, Earthquake hazard associated with deep well injection: A report to the U.S. Environmental Pro-tection Agency: U.S. Geological Survey Bulletin 1951.

National Research Council, 2012, Induced seismicity potential in en-ergy technologies: National Academies Press.

Segall, P., J.-R. Grasso, and A. Mossop, 1994, Poroelastic stressing and induced seismicity near the Lacq gas field, southwestern France: Journal of Geophysical Research, 99, B8, 15,423–15,438, http://dx.doi.org/10.1029/94JB00989.

Simpson, D. W. and W. Leith, 1985, The 1976 and 1984 Gazli, USSR, Earthquakes—Were they induced?: Bulletin of the Seismological Society of America, 75, no. 5, 1465–1468.

Warpinski, N., J. Du, and U. Zimmer, 2012, Measurements of hydrau-lic-fracture-induced seismicity in gas shales: SPE paper 151597.

Zoback, M. L. and M. D. Zoback, 1980, State of stress in the coter-minous United States: Journal of Geophysical Research, 85, B11, 6113–6156, http://dx.doi.org/10.1029/JB085iB11p06113.

Zoback, M. L. and M. D. Zoback, 1989, Tectonic stress field of the continental United States, in L. C. Pakiser and W. D. Mooney, eds, Geophysical framework of the continental United States: GSA Memoir 172, 523–539.

Corresponding author: [email protected]

the potential for induced seismicity in energy technologies

Documents