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75–820 PDF 2012

S. HRG. 112–532 

INDUCED SEISMICITY FROM ENERGY 

TECHNOLOGIES 

HEARING 

BEFORE THE

COMMITTEE ON 

ENERGY AND NATURAL RESOURCES 

UNITED STATES SENATE 

ONE HUNDRED TWELFTH CONGRESS 

SECOND SESSION 

TO

RECEIVE TESTIMONY ON THE POTENTIAL FOR INDUCED SEISMICITY 

FROM ENERGY TECHNOLOIGES, INCLUDING CARBON CAPTURE AND 

STORAGE, ENHANCED GEOTHERMAL SYSTEMS, PRODUCTION FROM 

GAS SHALES, AND ENHANCED OIL RECOVERY 

JUNE 19, 2012 

( 

Printed for the use of the 

Committee on Energy and Natural Resources 
(II) 

COMMITTEE ON ENERGY AND NATURAL RESOURCES 

JEFF BINGAMAN, New Mexico, Chairman 

RON WYDEN, Oregon 

TIM JOHNSON, South Dakota 

MARY L. LANDRIEU, Louisiana 

MARIA CANTWELL, Washington 

BERNARD SANDERS, Vermont 

DEBBIE STABENOW, Michigan 

MARK UDALL, Colorado 

JEANNE SHAHEEN, New Hampshire 

AL FRANKEN, Minnesota 

JOE MANCHIN, III, West Virginia 

CHRISTOPHER A. COONS, Delaware 

LISA MURKOWSKI, Alaska 

JOHN BARRASSO, Wyoming 

JAMES E. RISCH, Idaho 

MIKE LEE, Utah 

RAND PAUL, Kentucky 

DANIEL COATS, Indiana 

ROB PORTMAN, Ohio 

JOHN HOEVEN, North Dakota 

DEAN HELLER, Nevada 

BOB CORKER, Tennessee 

ROBERT M. SIMON, Staff Director 

SAM E. FOWLER, Chief Counsel 

MCKIE CAMPBELL, Republican Staff Director 

KAREN K. BILLUPS, Republican Chief Counsel 
(III) 

C O N T E N T S 

STATEMENTS 

Page 

Bingaman, Hon. Jeff, U.S. Senator From New Mexico ........................................ 1 

Hitzman, Murray W., Charles Fogarty, Professor of Economic Geology, Department of Geology and Geological Engineering, Colorado School of Mines, 

Golden, CO ............................................................................................................ 3 

Leith, William, Senior Science Advisor for Earthquake and Geologic Hazards, 

U.S. Geological Survey Department of the Interior .......................................... 10 

Murkowski, Hon. Lisa, U.S. Senator From Alaska ............................................... 2 

Petty, Susan, President and Chief Technology Officer, Alta Rock Energy, 

Inc, Seattle, WA ................................................................................................... 15 

Zoback, Mark D., Benjamin M. Page Professor of Earth Sciences, Department 

of Geophysics, Stanford University, Stanford, CA ............................................ 33 

APPENDIX 

Responses to additional questions .......................................................................... 49 

(1) 

INDUCED SEISMICITY FROM ENERGY 

TECHNOLOGIES 

TUESDAY, JUNE 19, 2012 

U.S. SENATE, COMMITTEE ON ENERGY AND NATURAL RESOURCES, Washington, DC. 

The committee met, pursuant to notice, at 10:03 a.m. in room 

SD–366, Dirksen Senate Office Building, Hon. Jeff Bingaman, 

chairman, presiding. 

OPENING STATEMENT OF HON. JEFF BINGAMAN, U.S. 

SENATOR FROM NEW MEXICO 

The CHAIRMAN. OK. Why don’t we get started? Senator Murkowski is delayed a very few minutes here, but asked us to go 

ahead and proceed. 

Welcome everyone to the hearing. This is on the potential for inducing manmade earthquakes from energy technologies. Many of 

the current and next generation energy technologies that are vital 

to our country’s future require the injection of fluids like water and 

carbon dioxide or other mixtures deep into the Earth’s subsurface. 

Geothermal energy extraction, geological carbon sequestration, 

the injection of waste water from hydraulic fracturing and enhanced oil recovery all require the injection and movement of fluids 

deep underground. Scientists have known for many decades that 

one potential side effect of pumping fluids in or out of the Earth 

is the creation of small to medium sized earthquakes. Though only 

a small number of recent seismic events here and abroad have been 

definitely linked to energy development, public concern has been 

raised about the potential for manmade earthquakes after seismic 

events that were felt in Arkansas and Oklahoma and Ohio and 

other places in the country. Those events in some cases were located near energy development and waste disposal sites. 

In 2010 I asked Secretary Chu to initiate a comprehensive and 

independent study by the National Academy of Sciences and the 

National Academy of Engineering to examine the possible scale, 

scope and consequences of seismicity induced by energy technologies. In particular, I asked them to focus on the potential for 

induced seismicity from enhanced geothermal systems, production 

from gas shales, enhanced oil recovery and carbon capture and 

storage. 

The Academy released their report this past Friday. The results 

provide a timely assessment of the potential hazards and risks of 

induced seismicity potential posed by these energy technologies. I 

want to thank the members of the Study Committee, the staff of 
2 

the National Academies and all of those associated with putting together this important report for their very hard work. 

The National Academy of Science’s Committee found that of all 

the energy related injection and extraction activities conducted in 

the United States only a small percentage have created earthquakes at levels noticeable to humans. None have caused significant damage to life or property. 

The committee also determined that because hydraulic fracturing 

for natural gas development typically involves the injection of relatively small amounts of fluid into localized areas. Hydraulic fracturing, itself, rarely triggers earthquakes large enough to be felt. 

Activities that inject greater amounts of fluid over longer periods 

of time, however, such as the injection of drilling waste water, pose 

a greater risk for causing noticeable earthquakes. 

Recent data from USGS suggests that the rate of earthquakes in 

the U.S. mid-continent has increased significantly in the past decade. The locations of these earthquakes are near many oil and gas 

extraction operations. As a result have raised public concern that 

they are the result of underground injection of drilling waste water. 

The study also indicates that injection and storing—injecting and 

storing vast amounts of carbon dioxide in the subsurface may pose 

a risk for seismicity that needs to be better understood and quantified through research. 

The discussion we’re having today is an important and timely 

one. As the National Academy’s report indicates risk from manmade earthquakes associated with energy technologies has been 

minimal and provided appropriate proactive measures are taken, 

may be effectively managed for the future. I look forward to hearing more about the topic from our panel of expert witnesses here. 

Let me defer to Senator Murkowski for any comments she has 

before I introduce the witnesses. 

STATEMENT OF HON. LISA MURKOWSKI, U.S. SENATOR 

FROM ALASKA 

Senator MURKOWSKI. Thank you, Mr. Chairman and good morning to all of our witnesses today. I do look forward to your testimony also. 

Over the past year or so I think we’ve all seen some of the trade 

press articles about issues of induced seismicity. While some of the 

headlines might look a bit sensational, it did seem that the true 

risk in reality is actually quite remote. But as such it’s good to get 

a reality check from the experts. That’s why you have been invited 

here today. 

The headline on this study from the NAS reads, ‘‘Federal Research concludes quake risk from drilling low, avoidable.’’ This covers geothermal wells, oil and gas wells and waste water wells. 

Really the unfortunate thing here is that the headline associates 

this report with drilling when drilling is perhaps not the issue so 

much as the actual permanent injection of waste water or carbon 

into an area where the pressures have become destabilized and 

some vibration then occurs. 

I think it’s good news that most of the seismic activity under discussion here, even with the hundreds of thousands of areas energy 

projects at play, have been quite small and often barely noticeable 
3 

to humans. None of this is to say that anyone should be dismissive 

of this discussion. I think we all know that energy development of 

all sources and in all places does have attendant risks and impacts. 

It’s not surprising to me to see that injecting and removing large 

volumes of fluids and gases underground might, under some conditions, cause vibrations to be felt above the ground. The question is 

whether that sort of seismicity is avoidable and manageable. 

The study that we’re looking at seems to indicate the answer is 

yes, which is also not surprising. But I’m interested to hear our 

other witnesses? views on the study. Since the study was only released on Friday, I realize that you may have more to say once 

you’ve had more time to actually study it carefully. But I do look 

forward to your initial impressions today. 

With that, I thank the Chairman. 

The CHAIRMAN. Thank you very much. 

Let me introduce our witnesses. 

First will be Dr. Murray Hitzman, who is a Professor with Colorado School of Mines. He’s also Chairman of the National Academy’s Committee that has prepared this report. So we thank you 

again for that heroic effort. 

Dr. William Leith is the Senior Science Advisor for Earthquake 

and Geologic Hazards with the Geological Survey. 

Ms. Susan Petty is President and Chief Technology Officer with 

Altarock Energy. Thank you very much for being here. 

Dr. Mark Zoback is a Professor at Stanford. He’s testified here 

before and we welcome him back. 

Dr. Hitzman, why don’t you go right ahead? 

If each of you could take 5 or 6 minutes and tell us the main 

points you think we need to try to understand. Then we will undoubtedly have questions. 

STATEMENT OF MURRAY W. HITZMAN, CHARLES FOGARTY 

PROFESSOR OF ECONOMIC GEOLOGY, DEPARTMENT OF GEOLOGY AND GEOLOGICAL ENGINEERING, COLORADO 

SCHOOL OF MINES, GOLDEN, CO 

Mr. HITZMAN. Thank you very much. 

Chairman Bingaman, Ranking Member Murkowski and members 

of the committee, thank you for the invitation to address you. 

Although the vast majority of earthquakes that occur in the 

world each year have natural causes, some of these earthquakes 

and a number of lesser magnitude seismic events are related to 

human activities and are called induced seismic events or induced 

earthquakes. Since the 1920s we have recognized that pumping 

fluids into or out of the Earth has the potential to cause seismic 

imbalance that can be felt. Only a very small fraction of injection 

and extraction activities at hundreds of thousands of energy development sites in the U.S. have induced seismicity at levels that are 

noticeable to the public. 

However, seismic events caused by or likely related to energy developments have been measured and felt in a number of States. Although none of these events has resulted in loss of life or significant structural damage, their effects were felt by local residents, 

some of whom also experienced minor property damage. Anticipating public concern about the potential for induced seismicity re-
4 

lated to energy development, Chairman, Senator Bingaman, did request from DOE that they conduct a study of this issue through the 

National Research Council. 

The committee that wrote the NRC report released last Friday 

consisted of 11 experts in various aspects of seismicity and energy 

technologies from both academia and industry. 

The committee found that induced seismicity associated with 

fluid injection or withdrawal associated with energy development is 

caused, in most cases, by a change in pore pressure and/or change 

in stress in the subsurface in the presence of faults with specific 

properties and orientations and a critical state of stress in the 

rocks. The factor that appears to have the most direct consequence 

in regard to induced seismicity is the net fluid balance or put more 

simply, the total balance of fluid either introduced or taken out 

from the subsurface. Additional factors may also influence the way 

fluids affect the subsurface. 

The committee concluded that while the general mechanisms 

that create induced seismic events are well understood. We are currently unable to accurately predict the magnitude or occurrence of 

such events due to the lack of a comprehensive data on complex 

natural rocks or systems in the subsurface and the lack of validated predictive models. 

The committee found for the largest induced seismic events associated with energy projects were those that did not balance the 

large volumes of fluids injected into or extracted from the Earth. 

We emphasize this is a statistical observation. It suggests, however, that the net volume of fluid that is injected and/or extracted 

may serve as a proxy for the changes in subsurface stress conditions in pore pressure. 

I’m going to briefly discuss the induced seismicity potential now 

for each of the energy technologies that was asked for in the report. 

Although it felt induced seismicity has been documented with the 

development of geothermal resources, such development usually attempts to keep a mass balance between fluid volumes produced and 

fluids replaced by injection to extend the longevity of the energy resource. This fluid balance helps to maintain fairly constant reservoir pressure, close to the initial preproduction value and aids in 

reducing the potential for induced seismicity. 

Oil and gas extraction from a reservoir may cause induced seismic events. These events are rare, relative to the large number of 

oil and gas fields around the world and appear to be related to decrease in pore pressure as fluid has been drawn. 

Secondary recovery and enhanced oil recoveries or EOR for oil 

and gas production both involve injection of fluids into the subsurface to push more of the hydrocarbons out of the pore spaces 

and to maintain reservoir pressure. Approximately 151,000 injection wells are currently permitted in the U.S. 

For a combination of secondary recovery EOR and waste water 

disposal with only a very few documented incidents where the injection caused or is likely related to felt seismic events. 

Among the tens of thousands of wells used for enhanced oil recovery in the U.S. the committee did not find any documentation 

in the published literature of felt induced seismicity. 
5 

Shale formations also contain hydrocarbons. The extremely low 

permeability of these rocks has trapped the hydrocarbons and prevented them from migrating from the rock. The low permeability 

also prevents the hydrocarbons from easily flowing into a well bore 

without production stimulation. 

These types of unconventional reservoirs are developed by drilling rails horizontally through the reservoir rock and using hydraulic fracturing techniques to create new fractures in the reservoir to 

allow us to get the hydrocarbons out. About 35,000 hydraulically 

fractured shale wells exist in the U.S. Only one case of felt seismicity in the United States has been described in which hydraulic 

fracturing for shale gas development is suspected but not confirmed. Globally, one case of felt induced seismicity in Blackpool, 

England has been confirmed as being caused by hydraulic fracturing for shale gas development. 

The very low number of felt events relative to the large number 

of hydraulically fractured wells for shale gas is likely due to the 

short duration of injection of fluids and the limited fluid volumes 

used. 

In addition to the fluid injection directly related to energy development, injection wells drilled to dispose of waste water generated 

during oil and gas production are very common in the United 

States. Tens of thousands of waste water disposal wells are currently active. Although only a few induced seismic events have 

been linked to these disposal wells, the occurrence of these events 

has generated considerable public concern. 

Examination of these cases suggest casual links between the injection zones and previously unrecognized faults in the subsurface. 

Injection wells are used only for the purpose of waste water disposal normally do not have a detailed geologic review performed 

prior to injection and the data are often not available to make such 

a detailed review. Thus the location of the possible nearby faults 

is often not a standard part of citing and drilling these disposal 

wells. In addition, the presence of a fault does not necessarily 

imply an increased potential for induced seismicity. 

The majority of hazardous and non-hazardous waste water disposal wells do not pose a hazard for induced seismicity. However, 

the long term affects of any significant increases in the number of 

waste water disposal wells in a particular area on induced seismicity are unknown. 

Carbon capture and sequestration or CCS is also a means of disposing of fluids in the subsurface. The committee found that the 

risk of induced seismicity from CCS is currently difficult to accurately assess. With only a few small scale commercial projects overseas and several small demonstration projects underway in the 

U.S., there are few data available to evaluate the induced seismicity potential of this technology. 

The existing projects have involved relatively small injection volumes. CCS differs from the other energy technologies in that it involves continuous injection of carbon dioxide fluid at high rates, 

under pressure, for long periods of time. It is purposely intended 

for permanent storage. There’s no fluid withdrawal. 

Given that the potential magnitude from induced seismic event 

correlates strongly with a fault rupture area. Which in turn relates 
6 

to the magnitude of pore pressure change and the rock volume 

which exists, the committee determined that large scale CCS may 

have the potential for causing significant induced seismicity. 

The committee also investigated governmental responses to induced seismic events. Responses have been undertaken by a number of Federal and State agencies in a variety of ways. To date, 

Federal and State agencies have dealt with induced seismic events 

with different and localized actions. 

These actions have been successful, but they’ve been ad hoc in 

nature. With the potential for increased numbers of induced seismic events due to expanding energy development governmental 

agencies and research institutions may not have sufficient resources to address unexpected events. The committee concluded 

that forward looking, interagency cooperation to address potential 

induced seismicity is warranted. 

Methodologies can be developed for quantitative probabilistic 

hazard assessments of induced seismicity risk. The committee determined that such assessments should be undertaken before operations begin in areas with a known history of felt seismicity and 

updated in response to observed, potentially induced events. The 

committee suggested that practices that consider induced seismicity both before and during the actual operations of an energy 

project should be employed to develop best practices protocols specific to each of the energy technologies and to site location. 

Although induced seismic events have not resulted in loss of life 

or major damage to the U.S., their effects have been felt locally and 

they raise some concern about additional seismic activity and its 

consequences in areas where energy development is ongoing or 

planned. Further research is required to better understand and address the potential risks associated with induced seismicity. 

I’d like to thank the committee for its time and its interest in 

this subject. I request the balance of my written testimony be 

placed in the record. I certainly look forward to your questions. 

[The prepared statement of Mr. Hitzman follows:] 

PREPARED STATEMENT OF MURRAY W. HITZMAN, CHARLES FOGARTY PROFESSOR OF

ECONOMIC GEOLOGY, DEPARTMENT OF GEOLOGY AND GEOLOGICAL ENGINEERING, 

COLORADO SCHOOL OF MINES, GOLDEN, CO 

Chairman Bingaman, Ranking Member Murkowski, and members of the committee, I would like to thank you for the invitation to address you on the subject 

of induced seismicity potential in energy technologies. My name is Murray Hitzman. 

I am a professor of geology at the Colorado School of Mines in Golden, Colorado and 

served as the chair of the National Research Council Committee on Induced Seismicity Potential in Energy Technologies. The Research Council is the operating arm 

of the National Academy of Sciences, National Academy of Engineering, and the Institute of Medicine of the National Academies, chartered by Congress in 1863 to advise the government on matters of science and technology. I would like to thank the 

committee for the invitation to address it on the subject of induced seismicity potential in energy technologies. 

Although the vast majority of earthquakes that occur in the world each year have 

natural causes, some of these earthquakes and a number of lesser magnitude seismic events are related to human activities and are called ‘‘induced seismic events’’ 

or ‘‘induced earthquakes.’’ 

Induced seismic activity has been attributed to a range of human activities including the impoundment of large reservoirs behind dams, controlled explosions related 

to mining or construction, and underground nuclear tests. Energy technologies that 

involve injection or withdrawal of fluids from the subsurface can also create induced 

seismic events that can be measured and felt. 
7 

Since the 1920s we have recognized that pumping fluids into or out of the Earth 

has the potential to cause seismic events that can be felt. Only a very small fraction 

of injection and extraction activities at hundreds of thousands of energy development sites in the United States have induced seismicity at levels that are noticeable 

to the public. However, seismic events caused by or likely related to energy development have been measured and felt in Alabama, Arkansas, California, Colorado, Illinois, Louisiana, Mississippi, Nebraska, Nevada, New Mexico, Ohio, Oklahoma, and 

Texas. Although none of these events resulted in loss of life or significant structural 

damage, their effects were felt by local residents, some of whom also experienced 

minor property damage. Particularly in areas where natural seismic activity is uncommon and energy development is ongoing, these induced seismic events, though 

small in scale, can be disturbing to the public and raise concern about increased 

seismic activity and its potential consequences. 

Anticipating public concern about the potential for induced seismicity related to 

energy development, the Chairman of this Committee, Senator Bingaman, requested 

that the Department of Energy conduct a study of this issue through the National 

Research Council. The Chairman requested that this study examine the scale, scope, 

and consequences of seismicity induced during the injection of fluids related to energy production. The energy technologies to be considered included geothermal energy development, oil and gas production, including enhanced oil recovery and shale 

gas, and carbon capture and storage or CCS. The study was also to identify gaps 

in knowledge and research needed to advance the understanding of induced seismicity; to identify gaps in induced seismic hazard assessment methodologies and the 

research needed to close those gaps; and to assess options for interim steps toward 

best practices with regard to energy development and induced seismicity potential. 

The National Research Council (NRC) released the report Induced Seismicity Potential in Energy Technologies on June 15. 

The committee that wrote this NRC report consisted of eleven experts in various 

aspects of seismicity and energy technologies from academia and industry. The committee examined peer-reviewed literature, documents produced by federal and state 

agencies, online databases and resources, and information requested from and submitted by external sources. We heard from government and industry representatives. We also talked with members of the public familiar with the world’s largest 

geothermal operation at The Geysers at a public meeting in Berkeley, California. 

We also spoke to people familiar with shale gas development, enhanced oil recovery, 

waste water disposal from energy development, and CCS at meetings in Dallas, 

Texas and Irvine, California. Meetings were also held in Washington, D.C. and Denver, Colorado to explore induced seismicity in theory and in practice. 

This study took place during a period in which a number of small, felt seismic 

events occurred that were likely related to fluid injection for energy development. 

Because of their recent occurrence, peer-reviewed publications about most of these 

events were generally not available. However, knowing that these events and information about them would be anticipated in this report, the committee attempted to 

identify and seek information from as many 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. Through this process, the committee has engaged scientists and engineers from academia, industry, and government because 

each has credible information to add to better understanding of induced seismicity. 

The committee found that induced seismicity associated with fluid injection or 

withdrawal associated with energy development is caused in most cases by change 

in pore fluid pressure and/or change in stress in the subsurface in the presence of 

faults with specific properties and orientations and a critical state of stress in the 

rocks. The factor that appears to have the most direct consequence in regard to induced seismicity is the net fluid balance or put more simply, the total balance of 

fluid introduced into or removed from the subsurface. Additional factors may also 

influence the way fluids affect the subsurface. The committee concluded that while 

the general mechanisms that create induced seismic events are well understood, we 

are currently unable to accurately predict the magnitude or occurrence of such 

events due to the lack of comprehensive data on complex natural rock systems and 

the lack of validated predictive models. 

The committee found that the largest induced seismic events associated with energy projects reported in the technical literature are associated with projects that 

did not balance the large volumes of fluids injected into, or extracted from, the 

Earth. We emphasize that this is a statistical observation. It suggests, however, that 

the net volume of fluid that is injected and/or extracted may serve as a proxy for 

changes in subsurface stress conditions and pore pressure. The committee recognizes that coupled thermo-mechanical and chemo-mechanical effects may also play 

a role in changing subsurface stress conditions. 
8 

I will briefly discuss the potential for induced seismicity with each of the energy 

technologies that the committee considered, beginning with geothermal energy. 

Geothermal Energy 

The three different types of geothermal energy resources are: (1) ‘‘vapor-dominated’’, where primarily steam is contained in the pores or fractures of hot rock, (2) 

‘‘liquid-dominated’’, where primarily hot water is contained in the rock, and (3) ‘‘Enhanced Geothermal Systems’’ (EGS), where the resource is hot, dry rock that requires engineered stimulation to allow fluid movement for commercial development. 

Although felt induced seismicity has been documented with all three types of geothermal resources, geothermal development usually attempts to keep a mass balance between fluid volumes produced and fluids replaced by injection to extend the 

longevity of the energy resource. This fluid balance helps to maintain fairly constant 

reservoir pressure-close to the initial, pre-production value-and aids in reducing the 

potential for induced seismicity. 

Seismic monitoring at liquid-dominated geothermal fields in the western United 

States has demonstrated relatively few occurrences of felt induced seismicity. However, in vapor or steam dominated geothermal system at The Geysers in northern 

California, the large temperature difference between the injected fluid and the geothermal reservoir results in significant cooling of the hot subsurface reservoir rocks. 

This has resulted in a significant amount of observed induced seismicity. EGS technology is in the early stages of development. Many countries including the United 

States have pilot projects to test the potential for commercial production. In each 

case of active EGS development, at least some, generally minor levels of felt induced 

seismicity have been recorded. 

Conventional Oil & Gas 

Oil and gas extraction from a reservoir may cause induced seismic events. These 

events are rare relative to the large number of oil and gas fields around the world 

and appear to be related to decrease in pore pressure as fluid is withdrawn. 

Oil or gas reservoirs often reach a point when insufficient pressure exists to allow 

sufficient hydrocarbon recovery. Various technologies, including secondary recovery 

and tertiary recovery—also called enhanced oil recovery or EOR—can be used to extract some of the remaining oil and gas. Secondary recovery and EOR technologies 

both involve injection of fluids into the subsurface to push more of the trapped hydrocarbons out of the pore spaces in the reservoir and to maintain reservoir pore 

pressure. Secondary recovery often uses water injection or ‘‘waterflooding’’ and EOR 

technologies often inject carbon dioxide. Approximately 151,000 injection wells are 

currently permitted in the United States for a combination secondary recovery, 

EOR, and waste water disposal with only very few documented incidents where the 

injection caused or was likely related to felt seismic events. Secondary recoverythrough waterflooding-has been associated with very few felt induced seismic 

events. Among the tens of thousands of wells used for EOR in the United States, 

the committee did not find any documentation in the published literature of felt induced seismicity. 

Shale Gas 

Shale formations can also contain hydrocarbons-gas and/or oil. The extremely low 

permeability of these rocks has trapped the hydrocarbons and largely prevented 

them from migrating out of the rock. The low permeability also prevents the hydrocarbons from easily flowing into a well bore without production stimulation by the 

operator. These types of ‘‘unconventional’’ reservoirs are developed by drilling wells 

horizontally through the reservoir rock and using hydraulic fracturing techniques to 

create new fractures in the reservoir to allow the hydrocarbons to migrate up the 

well bore. This process is now commonly referred to as ‘‘fracking.’’ About 35,000 hydraulically fractured shale gas wells exist in the United States. Only one case of 

felt seismicity in the United States has been described in which hydraulic fracturing 

for shale gas development is suspected, but not confirmed. Globally only one case 

of felt induced seismicity at Blackpool, England has been confirmed as being caused 

by hydraulic fracturing for shale gas development. The very low number of felt 

events relative to the large number of hydraulically fractured wells for shale gas is 

likely due to the short duration of injection of fluids and the limited fluid volumes 

used in a small spatial area. 

Waste Water Disposal 

In addition to fluid injection directly related to energy development, injection 

wells drilled to dispose of waste water generated during oil and gas production, including during hydraulic fracturing, are very common in the United States. Tens of 

thousands of waste water disposal wells are currently active throughout the coun-
9 

try. Although only a few induced seismic events have been linked to these disposal 

wells, the occurrence of these events has generated considerable public concern. Examination of these cases suggests causal links between the injection zones and previously unrecognized faults in the subsurface. 

In contrast to wells for EOR which are sited and drilled for precise injection into 

well-characterized oil and gas reservoirs, injection wells used only for the purpose 

of waste water disposal normally do not have a detailed geologic review performed 

prior to injection and the data are often not available to make such a detailed review. Thus, the location of possible nearby faults is often not a standard part of 

siting and drilling these disposal wells. In addition, the presence of a fault does not 

necessarily imply an increased potential for induced seismicity. This creates challenges for the evaluation of potential sites for disposal injection wells that will minimize the possibility for induced seismic activity. 

Most waste water disposal wells typically involve injection at relatively low pressures into large porous aquifers that have high natural permeability, and are specifically targeted to accommodate large volumes of fluid. Of the well-documented 

cases of induced seismicity related to waste water fluid injection, many are associated with operations involving large amounts of fluid injection over significant periods of time. Thus, although a few occurrences of induced seismic activity associated 

with waste water injection have been documented, the majority of the hazardous 

and nonhazardous waste water disposal wells do not pose a hazard for induced seismicity. However, the long-term effects of any significant increases in the number of 

waste water disposal wells in particular areas on induced seismicity are unknown. 

Carbon capture and sequestration 

Carbon capture and sequestration—or CCS—is also a means of disposing of fluid 

in the subsurface. The committee found that the risk of induced seismicity from 

CCS is currently difficult to accurately assess. With only a few small-scale commercial projects overseas and several small-scale demonstration projects underway in 

the United States, there are few data available to evaluate the induced seismicity 

potential of this technology. The existing projects have involved very small injection 

volumes. CCS differs from other energy technologies in that it involves continuous 

injection of carbon dioxide fluid at high rates under pressure for long periods of 

time. It is purposely intended for permanent storage—meaning that there is no fluid 

withdrawal. Given that the potential magnitude of an induced seismic event correlates strongly with the fault rupture area, which in turn relates to the magnitude 

of pore pressure change and the rock volume in which it exists, the committee determined that large-scale CCS may have the potential for causing significant induced 

seismicity. 

The committee’s findings suggest that energy projects with large net volumes of 

injected or extracted fluids over long periods of time, such as long-term waste water 

disposal wells and CCS, appear to have a higher potential for larger induced seismic 

events. The magnitude and intensity of possible induced events would be dependent 

upon the physical conditions in the subsurface-state of stress in the rocks, presence 

of existing faults, fault properties, and pore pressure. 

The committee also investigated governmental responses to induced seismic 

events. Responses have been undertaken by a number of federal and state agencies 

in a variety of ways. Four federal agencies-the Environmental Protection Agency 

(EPA) the Bureau of Land Management (BLM), the U.S. Department of Agriculture 

Forest Service (USFS), and the U.S. Geological Survey (USGS)-and different state 

agencies have regulatory oversight, research roles and/or responsibilities related to 

different aspects of the underground injection activities that are associated with energy technologies. Currently EPA has primary regulatory responsibility for fluid injection under the Safe Drinking Water Act. It is important to note that the Safe 

Drinking Water Act does not explicitly address induced seismicity. 

To date, federal and state agencies have dealt with induced seismic events with 

different and localized actions. These actions have been successful but have been ad 

hoc in nature. With the potential for increased numbers of induced seismic events 

due to expanding energy development, government agencies and research institutions may not have sufficient resources to address unexpected events. The committee concluded that forward-looking interagency cooperation to address potential 

induced seismicity is warranted. 

Methodologies can be developed for quantitative, probabilistic hazard assessments 

of induced seismicity risk. The committee determined that such assessments should 

be undertaken before operations begin in areas with a known history of felt seismicity and updated in response to observed, potentially induced seismicity. The committee suggested that practices that consider induced seismicity both before and 

during the actual operation of an energy project should be employed to develop a 
10 

‘‘best practices’’ protocol specific to each energy technology and site location. The 

committee’s meetings with individuals from Anderson Springs and Cobb, California, 

who live with induced seismicity continuously generated by geothermal energy production at The Geysers were invaluable in understanding how such a best practices 

protocol works. 

Although induced seismic events have not resulted in loss of life or major damage 

in the United States, their effects have been felt locally, and they raise some concern about additional seismic activity and its consequences in areas where energy 

development is ongoing or planned. Further research is required to better understand and address the potential risks associated with induced seismicity. 

I would like to thank the committee for its time and interest in this subject and 

I look forward to questions. 

The CHAIRMAN. Thank you very much. 

Dr. Leith, go right ahead. 

STATEMENT OF WILLIAM LEITH, SENIOR SCIENCE ADVISOR 

FOR EARTHQUAKE AND GEOLOGIC HAZARDS, U.S. GEOLOGICAL SURVEY, DEPARTMENT OF THE INTERIOR 

Mr. LEITH. Mr. Chairman, members of the committee, thank you 

for inviting the USGS to testify at this hearing. 

The United States is expanding its use of technologies that involve the injection and production of fluid at depth. As detailed in 

the report released last week by the National Research Council, the 

practices employed in these technologies have the potential to induce earthquakes. I commend this committee for requesting that 

such a study be undertaken and the Department of Energy for 

commissioning and funding the study. The NRC panel has done an 

outstanding job and made a significant contribution on this important issue. 

Since 2011 the central and eastern portions of the U.S. have experienced a number of moderately strong earthquakes in areas of 

historically low seismicity. Of these, only the earthquake that occurred last August in Central Virginia is unequivocally a natural 

tectonic earthquake. In all of the other cases there arises the possibility that the earthquakes were induced by waste water disposal. 

The disposal of fluids by deep injection is occurring more frequently in recent years. The occurrence of induced seismicity associated with fluid disposal from natural gas production in particular 

has increased significantly since the expanded use of hydraulic 

fracturing. Although there appears to be very little hazard associated with hydraulic fracturing itself, the disposal of the waters that 

are produced with the gas does appear to be linked to increased 

earthquake activity. As evidence, Mr. Chairman, you mentioned recent research by USGS seismologist Bill Ellsworth and colleagues 

which has documented that magnitude 3 and larger earthquakes 

have significantly increased in the U.S. midcontinent since the year 

2000. Most of this increase in seismicity has occurred in areas of 

enhanced hydrocarbon production and hence, increased disposal of 

production related fluids. 

To understand this phenomena the key research questions are: 

One, what factors distinguish those injection activities that induced earthquakes from those that do not? 

Two, to what extent can the occurrence of earthquakes triggered 

by deep fluid injection be influenced by altering the operational 

procedures? 
11 

Three, can small induced earthquakes trigger much larger 

tectonic earthquakes? 

Four, what will be the magnitude of the largest induced earthquake from a specific injection operation? 

Five, what is the probability of ground motion from induced 

earthquakes reaching a damaging level at a particular 

injectionsite? 

We’re already working collaboratively with the Department of 

Energy and EPA on some of these issues in response to the President’s establishment of the Interagency Hydraulic Fracturing 

Working Group. The involvement of industry is welcomed here and 

may be essential to make progress on some of these questions. Also 

any Federal research dollars spent to minimize the risk of induced 

seismicity will serve multiple goals since not only is this research 

relevant to natural gas development, geothermal development and 

carbon sequestration, but it also addresses several important gaps 

in our understanding of the natural earthquake process and fault 

behavior. 

Currently the precise data on injection volumes, rates and pressures needed to address these research questions are simply lacking for many sites of induced seismicity. Data collection required 

by underground injection control permits may not be sufficient to 

make confident, cause and effect statements about injection induced earthquakes after the fact. Without more precise and complete data it will be very difficult to assess the earthquake hazard 

potential from the tens of thousands of UIC wells that are currently in operation. 

Looking forward, the Administration has proposed to significantly increase our efforts on induced seismicity in the coming Fiscal year as part of a comprehensive initiative to address potential 

environmental health and safety issues associated with hydraulic 

fracturing. We hope that the Congress will support that initiative. 

Thank you again for the opportunity to testify. I’d be happy to 

answer any questions you may have. 

[The prepared statement of Mr. Leith follows:] 

PREPARED STATEMENT OF WILLIAM LEITH, SENIOR SCIENCE ADVISOR FOR EARTHQUAKE AND GEOLOGIC HAZARDS, U.S. GEOLOGICAL SURVEY, DEPARTMENT OF THE

INTERIOR

Chairman Bingaman, Ranking Member Murkowski, members of the committee, 

thank you for inviting the U.S. Geological Survey (USGS) to testify at this hearing 

on induced seismicity. My name is Bill Leith. I am the Senior Science Advisor for 

Earthquake and Geologic Hazards at the U.S. Geological Survey (USGS). The USGS 

is the science agency for the Department of the Interior (DOI). 

As part of its strategy to meet future energy needs, limit emissions of greenhouse 

gases, and safely dispose of wastewater, the United States is expanding the use of 

technologies that involve the injection, and in some cases the associated production, 

of fluid at depth. As detailed in the report released last week by the National Research Council (NRC), Induced Seismicity Potential in Energy Technologies (hereafter, NRC report), the injection and production practices employed in these technologies have, to varying degrees, the potential to introduce earthquake hazards. I 

would like to commend this committee for requesting that such a study be undertaken and the Department of Energy (DOE) for funding the study. The members 

of the National Research Council panel who wrote the report have done an outstanding job and have made a significant and lasting contribution to the public discourse on this important issue. 

The USGS is well positioned to provide solutions for challenging problems associated with meeting the Nation’s future energy needs. Various new approaches to 
12 

produce oil and gas and alternative energy entail deep injection of fluid that can 

induce earthquakes. The cause and effect of induced earthquakes pose a number of 

risks that must be understood. USGS scientists, along with scientists from the National Labs and Universities funded by DOE, are already involved in studying a 

number of these injection projects, and we possess substantial expertise in the associated science and technology of mitigating the effects of induced earthquakes. 

I summarize here the research topics that the USGS can address in order to assist the Nation in meeting its future energy needs through an improved understanding of induced seismicity that leads to mitigation of the associated risks. 

To put this hazard in perspective, since the beginning of 2011 the central and 

eastern portions of the United States have experienced a number of moderately 

strong earthquakes in areas of historically low earthquake hazard. These include 

earthquakes of magnitude (M) 4.7 in central Arkansas on February 27, 2011; M5.3 

near Trinidad, Colorado on August 23, 2011; M5.8 in central Virginia also on August 23, 2011; M4.8 in southeastern Texas on October 20, 2011; M5.6 in central 

Oklahoma on November 6, 2011; M4.0 in Youngstown, Ohio, on December 31, 2011; 

and M4.8 in east Texas on May 17, 2012. Of these, only the central Virginia earthquake is unequivocally a natural tectonic earthquake. In all of the other cases, there 

is scientific evidence to at least raise the possibility that the earthquakes were induced by wastewater disposal or other oil-and gas-related activities. Research completed to date strongly supports the conclusion that the earthquakes in Arkansas, 

Colorado and Ohio were induced by wastewater injection. Investigations into the nature of the Oklahoma and Texas earthquakes are in progress. 

The disposal of wastewater from oil and gas production by injection into deep geologic formations is a process that is being used more frequently in recent years. The 

occurrence of induced seismicity associated with wastewater disposal from natural 

gas production, in particular, has increased significantly since the development of 

technologies to facilitate production of gas from shale and tight sand formations. 

While there appears to be little seismic hazard associated with the hydraulic fracturing process that prepares the shale for production (hydrofracturing), the disposal 

of waters produced with the gas does appear to be linked to increased seismicity, 

as was made evident by the earthquake sequence near the Dallas-Fort Worth airport in 2008 and 2009. In addition, recent research by USGS seismologist Bill Ellsworth and colleagues has documented that M3 and larger earthquakes have significantly increased in the U.S. mid-continent since 2000, from a long-term average of 

21 such earthquakes per year between 1970 and 2000, to 31 per year during 2000- 

2008, to 151 per year since 2008. Most of this increase in seismicity has occurred 

in areas of enhanced hydrocarbon production and, hence, increased disposal of production-related fluids. 

Industry has been working to expand the development of unconventional geothermal resources known as Enhanced Geothermal Systems (EGS), because of their 

significant potential to contribute to the U.S. domestic energy mix. These geothermal resources are widespread throughout the United States and are areas of 

high heat flow but low permeability. To make EGS projects viable, the permeability 

of geologic formations must be enhanced by injecting fluid at high pressure into the 

low-permeability formations and inducing shear slip on pre-existing fractures. This 

process of permeability enhancement generally induces a large number of very small 

earthquakes with magnitudes less than 2 (microearthquakes). The microearthquakes provide critical information on the spatial extent and effectiveness of reservoir creation. Depending on the circumstances, however, the resulting seismicity 

can have serious, unintended consequences, such as project termination, if any of 

the induced events are sufficiently large (greater than magnitude 4) to result in surface damage or disturbance to nearby residents. As a means to address these issues, 

the DOE published an induced seismicity protocol in 2012, which is cited in the 

NRC study as ‘‘a reasonable initial model for dealing with induced seismicity that 

can serve as a template for other energy technologies.’’ 

As emphasized in the NRC report, there is a potential seismic hazard associated 

with geologic carbon sequestration projects that involve the injection of very large 

quantities of CO2 into sedimentary basins, some of which are located in or near 

major urban centers of the eastern and central United States. Because carbon dioxide storage requires a high porosity formation of high permeability that is capped 

by an impermeable seal (e.g., shale), there are two important sources of seismic risk. 

The first type of risk is due to the possibility of a large magnitude earthquake that 

causes damage to structures in the environs of the project. More importantly, there 

is the possibility that an induced earthquake rupture would breach the cap rock allowing the CO2 to escape. 

Historically, the USGS has contributed significantly toward understanding seismicity induced by liquid injection, starting with the Rocky Mountain Arsenal in the 
13 

1960’s, where it was first discovered that liquid waste disposal operations can cause 

earthquakes. Between 1969 and 1973, the USGS conducted a unique experiment in 

earthquake control at the Rangely oil field in western Colorado. This experiment 

confirmed the predicted effect of fluid pressure on earthquake activity and demonstrated how earthquakes can be controlled by regulating the fluid pressure in a 

fault zone. The state of the science on the earthquake hazard related to deep well 

injection was summarized by the USGS in 1990, in a review that proposed criteria 

to assist in regulating well operations so as to minimize the hazard. This study was 

part of a co-operative agreement with EPA and was used to inform site selection 

and operating criteria during the development of underground injection control regulations for Class I Hazardous wells. This 1990 study is the most recent review of 

this topic but is likely to be superseded by the new NRC report. With support from 

our partners, USGS scientists are currently investigating induced seismicity associated with brine disposal operations in the Paradox Basin of Colorado and the Raton 

Basin coal bed methane field along the Colorado-New Mexico border. We and our 

partners, including the DOE, are also investigating the state of stress, heat flow, 

and microseismicity within geothermal reservoirs to evaluate the effectiveness of hydraulic stimulation for EGS. The combination within USGS of expertise in both energy science and earthquake science has proven particularly effective in addressing 

current issues. 

Some of the key questions that arise in connection with fluid injection and production projects are: 

• What factors distinguish injection activities that induce earthquakes from those 

that do not? 

• To what extent can the occurrence of earthquakes induced by deep liquid-injection and production operations be influenced by altering operational procedures 

in ways that do not compromise project objectives? 

• Can deep liquid-injection operations interact with regional tectonics to influence 

the occurrence of natural earthquakes by, for example, causing them to occur 

earlier than they might have otherwise? Similarly, can induced earthquakes 

trigger much larger tectonic earthquakes? 

• What distribution of earthquakes (frequency of occurrence as a function of magnitude) is likely to result from a specified injection operation? 

• What is likely to be the magnitude of the largest induced earthquake from a 

specific injection operation? 

• What is the probability of ground motion from induced earthquakes reaching a 

damaging level at a particular site, and what would be the consequences (e.g., 

injury and/or structural damage)? 

In the recent NRC report and in workshops sponsored by the DOE, , a common 

need has been identified for research to address the science questions posed above. 

The USGS, as an independent and unbiased science organization, can play a major 

role in studying, assessing, and providing solutions to these problems. We are already working collaboratively with DOE and U.S. Environmental Protection Agency 

on some of these issues, in response to the President’s establishment of the interagency hydraulic fracturing working group, as well as with the States. 

Although our primary research is directed at natural earthquakes and 

hydrogeology, we have in the past assessed the hazards associated with induced 

earthquakes due to mining operations, reservoir impoundment, oil and gas production and fluid injection. Thus, for many of these items, the research would mostly 

involve modifying existing approaches to the specialized requirements of fluid injection-and production-induced earthquakes. 

Addressing these science problems will require a multidisciplinary approach that 

includes research in seismology, hydrology, crustal deformation, laboratory rock mechanics, in situ stress and fracture permeability, heat transport, fluid flow and other 

areas of study. The research activities might potentially include field-scale experiments, laboratory rock mechanics experiments, and the development and application 

of numerical models that simulate the effects of fluid injection operations on fracturing, fault reactivation and stress transfer, especially in low-permeability formations. Careful analyses of published case histories involving seismicity caused by 

fluid injection and production operations would be an important component of a 

comprehensive research program. 

The involvement of industry is welcomed and may be essential to make progress 

on many of the key science questions. We see value in establishing an experimental 

site, or sites, in cooperation with industry and other agencies that could further the 

early work on induced earthquake triggering that was conducted so long ago at the 

Rangely field in Colorado. We note that DOE has in fact proposed a government- 
14 

managed test site for EGS in its FY13 budget proposal, at which such R&D could 

be conducted in a carefully controlled and instrumented environment. 

While a comprehensive effort is needed, and is called for in the NRC’s recent report, any federal research dollars spent to minimize the risks of induced seismicity 

will serve multiple goals. Not only is this research relevant to shale gas development, geothermal development and carbon sequestration, but it also addresses several important gaps in our knowledge of the natural earthquake process and fault 

behavior. 

I wish to expand on two of the findings and recommendations in the NRC report: 

The first of these is what I will call the ‘‘data gap’’, for which the report recommends, ‘‘Data related to fluid injection... should be collected by state and federal 

regulatory authorities in a common format and made publicly available (through a 

coordinating body such as the USGS).’’ Currently, the data on injection volumes, 

rates and pressures needed to address many of the research questions above are 

simply lacking for many sites of induced seismicity. Permitting requirements for 

Underground Injection Control (UIC) wells are defined under Safe Drinking Water 

Act regulations, administered by the EPA and the states. Unless the potential for 

induced seismicity has been identified as a local risk prior to issuing a UIC permit, 

data collection required under these permits may not be sufficient to make confident 

cause-and-effect statements about injection-induced earthquakes after the fact, making it difficult to provide useful information to the regulating authorities about 

whether a particular disposal operation has or will have increased local earthquake 

risk. 

Without more precise and complete data, it will be very difficult to assess the hazard potential from the tens of thousands of UIC wells that are currently in operation and for which their earthquake potential is unknown. An equal challenge is 

posed by UIC wells that may be permitted and become active injectors in the future, 

particularly if the permitting agency for the well is not cognizant of the associated 

earthquake hazard, or not in communication with parties that would be sensitive 

to a change in earthquake risk. For example, how close to an existing nuclear power 

plant or a dam is ‘‘too close’’ to site a disposal well permitted for a specified volume 

and pressure? Whose responsibility is it to evaluate the risk? Who is responsible for 

notifying the parties at risk? Who carries the liability should a damaging earthquake occur? Getting answers to these questions requires accurately assessing the 

induced-earthquake hazard, but at present the needed statistics are lacking because 

of the data gap. The NRC report provides some helpful guidance on how to develop 

‘‘best practice’’ protocols that could help to close the data gap if implemented The 

report cites the recently published DOE IS protocol as an important step towards 

establishing a best practices effort. 

The NRC report also found: ‘‘To date, the various agencies have dealt with induced seismic events with different and localized actions. These efforts to respond 

to potential induced seismic events have been successful but have been ad hoc in 

nature.’’ Above in this testimony, I detailed the large number of induced or potentially induced earthquakes that have occurred in 2011 and 2012. Further, USGS scientists have also documented a seven-fold increase since 2008 in the seismicity of 

the central U.S., an increase that is largely associated with areas of wastewater disposal from oil, gas and coal-bed methane production. Scientifically, USGS has a 

depth of expertise relevant to understanding induced seismicity and the increasing 

demand for better monitoring, analysis, assessment, and public information. We 

have also worked closely with colleagues in academia and the State Geological Surveys, which have also seen increasing demands. 

To meet these increasing demands, we have increased research efforts within our 

current budget. Looking forward, the Administration has proposed to significantly 

increase our efforts on induced seismicity in the coming fiscal year, as part of a comprehensive initiative to address potential environmental, health, and safety issues 

associated with hydraulic fracturing, and we hope that the Congress will support 

that initiative. 

Thank you again for the opportunity to testify and for your attention to this important matter. I would be happy to answer any questions you may have. 

The CHAIRMAN. Thank you very much. 

Ms. Petty. 
15 

STATEMENT OF SUSAN PETTY, PRESIDENT AND CHIEF TECHNOLOGY OFFICER, ALTAROCK ENERGY, INC, SEATTLE, WA 

Ms. PETTY. Thank you, Mr. Chairman and members of the committee. Good morning. 

I really appreciate this opportunity to talk to you about our experiences with the mitigation of induced seismicity in the geothermal 

industry. Over the past few years injection induced seismicity has 

become an increasingly important issue that Earth scientists working in the geothermal, mining, petroleum and other industries 

must address. At Altarock Energy we’re in the trenches focused on 

developing advanced technology to reduce the cost of enhanced geothermal systems to extend the ability to use this base load renewable energy source across the United States. 

This resource is so large that recovering even a small fraction of 

it could provide electric power and heat sufficient to supply 10 percent or more of the Nation’s need for thousands of years to come. 

The MIT study of the future of geothermal energy in 2007 projected 

that there is the potential to generate over 2 million megawatts 

across the U.S. if only 2 percent of this resource can be recovered. 

The USGS found that there is the potential for more than 500,000 

megawatts in the Western United States alone. 

In order to develop this vast resource we need a way to recover 

the heat by injecting water into a well, have it move through the 

hot rock and pick up heat and then be produced through production wells. To do this, we create a network of fine fractures that 

access a large volume of hot rock. Doing this requires pumping cold 

water into the ground at relatively modest pressures and then 

using the temperature contrast combined with the pressure to extend existing fractures and planes of weakness outward from the 

well. 

While this is not new technology, it is technology that is still in 

development. Advances are needed to both reduce the risks associated with the development and to improve economics. One of the 

areas of risk is the possibility that seismicity of concern to people 

will be induced during the process of creating the reservoir or operating the EGS project long term. By looking at our past experiences 

with injection and induced seismicity, we can gain a better understanding of how to select project sites with—and operate the reservoir, so that we can reduce the risk of problematic induced seismicity. Our experience with the Newberry EGS Demonstration 

Projects, I feel, can help us grasp the issues and the potential solutions to these issues that will affect any future projects that use 

EGS technology. 

Injection induced seismicity occurs when the fluid pressure in a 

fault or fracture reaches a critical value above which the friction 

preventing slip is overcome. 

This concept was proposed in 1959. 

Inadvertently demonstrated at the Rocky Mountain Arsenal in 

1962. 

Further tested at the Rangely Oil Field in 1969. 

Has been incorporated into continuous injection operations at 

Paradox Valley since 1996. 

EGS reservoir creation relies upon controlled induced seismicity 

to create the high surface area fracture paths needed for sustain-
16 

able and economic heat extraction. The lessons learned from past 

EGS projects, in particular to projects along the Rhine Garben in 

Europe, are being used to refine the plans for future projects. 

It’s important to understand that creation of the EGS reservoir 

necessarily causes tiny seismic events when the small fractures slip 

and slide against one another. We use these tiny seismic events, 

as does the oil and gas industry, to map the fractures as we form 

them. What we don’t want is larger faults to slip during this process and release enough energy for people to feel. 

The energy released measured by the moment magnitude, commonly thought of as the Richter scale, is only one aspect of whether 

the seismicity will be felt by people or not. The rocks that the energy passes through and the types of soils near the surface as well 

as the structures that sit on those soils all contribute to whether 

seismicity is problematic or not. 

One of the things we need to do to better communicate about injection induced seismicity is understand that that relationship between the magnitude of the event at depth and what people might 

potentially feel on the surface, the ground shaking. It would be better to talk about the risk of ground shaking than to talk about the 

risk around a particular magnitude of event occurring. I might add 

that the mining industry has long had regulations regarding 

ground shaking that we can maybe look to, to get this kind of experience. 

For the Newberry EGS demonstration project we have gone 

through a process of both developing an induced seismicity mitigation protocol for the project activities and also communicating with 

the public about the project and the issues associated with induced 

seismicity. Three Federal agencies were involved with the permitting process, the Department of Energy, the Bureau of Land Management and the Forest Service. Only the DOE had staff with expertise in induced seismicity to help us through the process. We 

had, therefore, to inform and educate other regulators about the 

methods used to assess the potential risks related to induced seismicity and the possibilities for mitigating those risks. 

The most difficult part of the induced seismicity hazards assessment was commuting the information it contains to the public. The 

ability of scientists to explain risk to the general public is limited 

by the public’s familiarity with that risk. Using maps and graphics 

help, but the language we have for discussing seismicity is difficult 

for the best of us to relate to our everyday lives. 

One of the interesting aspects of our public outreach effort is that 

in this region of tectonic activity with volcanoes and subduction 

zones as well as offshore large faults and fractures, people are 

much more concerned with potential for ground water contamination or water use impacts than they are with induced seismicity. 

While the Newberry area itself is very seismically quiet and quite 

remote from people, Oregonians are regularly rattled by temblors 

mostly on offshore faults. So they are familiar with small, natural 

seismic events. 

On the other hand this is arid area with little water and little 

rainfall. Water is of key importance. It’s in scarce supply. The focus 

by the regulators on induced seismicity took attention away from 

the key issue for the public which is water. 
17 

The result of a public outreach on our communication with regulators, as well as the expert input of the DOE, was a mitigation 

protocol that should enable us to both conduct our project and reduce the risk of felt seismicity. Our effort at Newberry is far more 

extensive and in depth. What is required of operators of waste 

water disposal wells with the risk, based on past experience, is far 

higher than what we have at Newberry. 

What can we take away from our experience with the Newberry 

project and with other EGS projects? 

Project citing can help us to reduce the risk and also the concerns of the public about that risk. We need to site projects away 

from large populations and dense populations until we better understand the risks surrounding this technology. 

We need to avoid areas with large faults. How far away do we 

need to be from those faults? We don’t yet know. That’s something 

that needs further research. 

Existing background data on seismicity is crucial for site selection and for gathering the information needed for permitting and 

operation of these sites. 

Public outreach is very important. But communication with regulators is equally so. Risk assessment results are difficult to explain 

to both the public and to regulators. So we need to select experts 

to write up and communicate these results, who have excellent 

communication skills. 

Graphics are needed. But they need to be easy to explain and understand. 

We also need to work with the press to get the message across. 

We have to provide data and graphics to reporters to help them understand the project. I have to say that this has been one area that 

has really been very difficult. I think has resulted in a lot of misunderstanding about what’s going on in this technology. 

We also need to identify key local issues. We don’t want to let 

induced seismicity dominate the discussion if it isn’t the key issue. 

Induced seismicity mitigation protocol for all injection related 

projects in the energy interest—industry that’s consistent across 

the technologies would be a useful tool for both project developers 

and regulators. 

Thank you. 

[The prepared statement of Ms. Petty follows:] 
18 

PREPARED STATEMENT OF SUSAN PETTY, PRESIDENT AND CHIEF TECHNOLOGY

OFFICER, ALTATROCK ENERGY, INC. SEATTLE, WA 
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The CHAIRMAN. Thank you very much. 

Dr. Zoback. 

STATEMENT OF MARK D. ZOBACK, BENJAMIN M. PAGE PROFESSOR OF EARTH SCIENCES, DEPARTMENT OF GEOPHYSICS, STANFORD UNIVERSITY, STANFORD, CA 

Mr. ZOBACK. Chairman Bingaman, Senator Murkowski and committee members, thank you for asking me to testify today. 

My name is Mark Zoback. I’m a Professor of Geophysics at Stanford University. My field of expertise is in quantifying the geologic 

processes in the Earth that control earthquakes and hydraulic fracture propagation. I’ve been doing this research for over 30 years. 

While I was not a member of the NRC Committee chaired by 

Professor Hitzman, I did have the opportunity to speak to them 

about the issues I’ll talk to you about today. Let me say at the outset, that I’m in full agreement with the principle findings of their 

report. 

I want to limit my comments today to discussing earthquakes 

and energy technologies in 2 specific contexts. 

First will be the earthquakes triggered by injection of waste 

water. Of course of particular interest has been the injection of the 

flow back water coming out from shale gas wells following hydraulic fracturing. 

Second, I want to comment briefly about the potential for triggered seismicity associated with the large scale carbon capture and 

storage or CCS, as it is widely known. 
34 

As Dr. Leith pointed out, in 2011 the relatively stable interior of 

the U.S. was struck by a surprising number of small to moderate 

size, but still widely felt earthquakes. Most of these events, as he 

indicated, were the kinds of natural events that occur from time to 

time in intra-plate regions. But a number of the small to moderate 

earthquakes that did occur in 2011 appeared to be associated with 

the disposal of waste water, at least in part related to shale gas 

production. Seismic events associated with waste water in 2011 include the earthquakes near Guy, Arkansas and those near Youngstown, Ohio. 

It is understandable that the occurrence of injection related 

earthquakes is of concern to the public, the government and industry alike. I think it is clear that with proper planning, monitoring 

and response, the occurrence of small to moderate earthquakes associated with waste injection can be reduced and the risks associated with these events effectively managed. 

Five straight forward steps can be taken to reduce the probability of triggering seismicity whenever we inject fluid into the 

subsurface. 

First, and as Susan Petty just pointed out, we need to avoid injection into faults in brittle rock. While this may seem like a nobrainer, there’s not always a sufficient site characterization prior 

to approval of an injectionsite. In fact EPA guidelines does not include the consideration of triggered seismicity among its requirements. 

Second, formations need to be selected that minimize the pore 

pressure changes. It is the increase of pore pressure that is the 

problem. We can minimize that increase in pore pressure by careful 

selection of formations used for injection. 

Third, local seismic monitoring arrays should be installed when 

there is a potential for triggered seismicity. 

Fourth, protocols should be established in advance to define how 

operations would be modified if seismicity were to be triggered. 

These kinds of proactive steps, I think, will go a long way toward 

making the rare occurrence of these events even more rare and assure the public that their safety is being protected. 

I’d now like to comment briefly about the potential for triggered 

seismicity associated with large scale carbon capture and storage. 

My colleague, Steve Gorelick and I, have recently pointed out that 

not only would large scale CCS be an extremely costly endeavor, 

there is a high probability that earthquakes will be triggered by injection of the enormous volumes of CO2 associated with large scale 

CCS in many regions currently being considered. 

There are 2 issues I want to emphasize in particular. 

First, our principle concern is not the probability of triggering 

large earthquakes. Large faults are required to produce large 

earthquakes. We assume that such faults would be detected and 

thus avoided by careful site characterization studies. 

Our concern is that even small to moderate size earthquakes 

would threaten the seal integrity of the formations being used to 

store the CO2. Studies by other scientists have shown that a leak 

rate from an underground CO2 storage reservoir of less than 1 percent per thousand years is required for CCS to achieve the same 

climate benefits as switching to renewable energy sources. 
35 

Second, it’s important to emphasize that we recognize that CCS 

can be a valuable and useful tool for reducing greenhouse gas emissions in specific situations. Our concern is whether CCS can be a 

viable strategy for achieving global greenhouse gas reductions and 

appropriate positive effects on climate change. From a global perspective, if large scale CCS is to significantly contribute to reducing 

the accumulation of greenhouse gases, it must operate at a massive 

scale on the order of the volume injected has to be on the order of 

the 27 billion barrels of oil that are produced each year around the 

world. So it’s a truly massive undertaking. 

Now multiple lines of evidence indicate that pre-existing faults 

found in brittle rocks almost everywhere in the Earth’s crust are 

close to frictional failure. In fact, over time periods of just a few 

decades, modern seismic networks have shown us that earthquakes 

occur nearly everywhere in continental interiors. 

So in the light of the risk posed to a CO2 repository by even 

small to moderate sized earthquakes, formations for suitable large 

scale injection of CO2 must be well sealed by impermeable overlying strata. 

They must be weakly cemented so as to not fail through brittle 

faulting. 

They must be porous, permeable and laterally extensive to accommodate large volumes of CO2 with minimal pressure increases. 

Thus the issue is not whether CO2 can be safely stored at a given 

site. The issue is whether the capacity exists for sufficient volumes 

of CO2 to be stored in geologic formations for it to have a beneficial 

effect on climate change. In this contest—in this context, it must 

be recognized that large scale CCS will be an extremely expensive 

and risky strategy for achieving significant reductions in greenhouse gas emissions. 

Mr. Chairman, Senator Murkowski, members of the committee, 

thank you for the opportunity to speak to you today. 

[The prepared statement of Mr. Zoback follows:] 

PREPARED STATEMENT OF MARK D. ZOBACK, BENJAMIN M. PAGE PROFESSOR OF

EARCH SCIENCES, DEPARTMENT OF GEOPHYSICS, STANFORD UNIVERSITY, STANFORD, CA 

Chairman Bingaman, Senator Murkowski and members of the committee, thank 

you for asking me to testify today. My name is Mark Zoback, I am a Professor of 

Geophysics at Stanford University. For your general information, I last spoke to this 

committee in October as a member of the Secretary of Energy’s Advisory Board 

Shale Gas Subcommittee. I also served on the National Academy of Engineering 

committee that investigated the Deepwater Horizon accident. My field of expertise 

is in quantifying geologic processes in the earth that control earthquakes and hydraulic fracture propagation. I have been doing research in these fields for over 30 

years ago. My PhD students and I have been carrying out a number of collaborative 

research projects seeking to better understand these processes in the context of carbon capture and storage and production from shale gas reservoirs. 

While I was not a member of the NRC committee chaired by Professor Hitzman, 

I did have the opportunity to speak with the committee about the issues I’ll comment upon today. Let me say at the outset that I am in full agreement with the 

principal findings their report. 

Today, I will limit my comments to discussing earthquakes and energy technologies in two specific contexts. First, will be earthquakes triggered by injection of 

wastewater. While wastewater can come from many sources, of particular interest 

in the past few years has been the injection of the flow-back water coming out of 

shale gas wells following hydraulic fracturing. Second, I want to comment briefly 
36 

about the potential for triggered seismicity associated large-scale carbon capture 

and storage, or CCS, as it is widely known. 

In most cases, if earthquakes are triggered by fluid injection it is because injecting fluid increases the pore pressure at depth. The increase in pore pressure reduces 

the frictional resistance to slip on pre-existing faults, allowing elastic energy already 

stored in the rock to be released in earthquakes. For the cases I will speak about 

today, the earthquakes in question would have occurred someday as a natural geologic process—injection could simply advance their time of occurrence. 

I have provided the committee staff with recently published papers I’ve written 

on these topics to provide more details. 

Earthquakes associated with wastewater injection 

In 2011 the relatively stable interior of the U.S. was struck by a surprising number of small-to-moderate, but widely felt earthquakes. Most of these were natural 

events, the types of earthquakes that occur from time to time in all intraplate regions. The magnitude 5.8 that occurred in northern Virginia on Aug. 23, 2011 that 

was felt throughout the northeast and damaged the Washington Monument was one 

of these natural events. While the magnitude of this event was unusual for this part 

of the world, the Aug. 23rd earthquake occurred in the Central Virginia seismic 

zone, an area known for many decades to produce relatively frequent small earthquakes. 

This said, a number of the small-to-moderate earthquakes that occurred in the interior of the U.S. in 2011 appear to be associated with the disposal of wastewater, 

at least in part related to shale gas production. 

Following hydraulic fracturing of shale gas wells, the water that was injected during hydraulic fracturing is flowed back out of the well. The amount of water that 

flows back after fracturing varies from region to region. It’s typical for 25-50% of 

injected water to flow back. While the chemicals that comprise the fracturing fluid 

are relatively benign, the flow-back water can be contaminated with brine, metals 

and potentially dangerous chemicals picked up from the shale and must be disposed 

of properly. 

Seismic events associated with injection of wastewater in 2011 include the earthquakes near Guy, Ark., where the largest earthquake was a magnitude-4.7 event 

on Feb. 27th and the earthquakes that occurred on Christmas Eve and New Year’s 

Eve near Youngstown, Ohio. The largest Youngstown event was magnitude 4.0. It 

is understandable that the occurrence of injection-related earthquakes is of concern 

to the public, government officials and industry alike. 

I believe that with proper planning, monitoring and response, the occurrence of 

small-to-moderate earthquakes associated with fluid injection can be reduced and 

the risks associated with such events effectively managed. No earthquake triggered 

by fluid injection has ever caused serious injury or significant damage. Moreover, 

approximately 140,000 Class II wastewater disposal wells have been operating safely and without incident in the U.S. for many decades. 

Five straightforward steps can be taken to reduce the probability of triggering 

seismicity whenever we inject fluid into the subsurface. First, it is important to 

avoid injection into faults in brittle rock. While this may seem a ‘‘no-brainer’’, there 

is not always sufficient site characterization prior to approval of a injection site. Second, formations should be selected for injection (and injection rates limited) so as 

to minimize pore pressure changes. Third, local seismic monitoring arrays should 

be installed when there is a potential for injection to trigger seismicity. Fourth, protocols should be established in advance to define how operations would be modified 

if seismicity were to be triggered. And fifth, operators need to be prepared to reduce 

injection rates or abandon injection wells if triggered seismicity poses any hazard. 

These five steps provide regulators and operating companies with a framework for 

reducing the risk associated with triggered earthquakes. 

In addition, the re-cycling of flow-back water (for use in subsequent hydraulic 

fracturing operations) is becoming increasingly common (especially in the northeastern U.S.). This is a very welcome development. Re-use of flow-back water avoids 

potential problems associated with transport and injection flow-back water or the 

expense and difficulty of extensive water treatment operations. 

It is important to note that the extremely small microseismic events occur during 

hydraulic fracturing operations. These microseismic events affect a very small volume of rock and release, on average, about the same amount of energy as a gallon 

of milk falling off a kitchen counter. The reason these events are so small is that 

pressurization during hydraulic fracturing affects only limited volumes of rock (typically several hundred meters in extent) and pressurization typically lasts only a few 

hours. A few very small earthquakes have occurred during hydraulic fracturing 
37 

(such as a magnitude-2.3 earthquake near Blackpool, England, in April 2011), but 

such events are extremely rare. 

It is important for the public to recognize that the risks posed by injection of 

wastewater are extremely low. In addition, the risks can be minimized further 

through proper study and planning prior to injection, careful monitoring in areas 

where there is a possibility that seismicity might be triggered, and operators and 

regulators taking a proactive response if triggered seismicity was to occur. 

Earthquake potential and large-scale carbon storage 

I would now like to comment briefly about the potential for triggered seismicity 

associated large-scale carbon capture and storage. My colleague Steve Gorelick and 

I have recently pointed out that not only would large-scale CCS be an extremely 

costly endeavor, there is a high probability that earthquakes will be triggered by 

injection of the enormous volumes CO2 associated with large-scale CCS. 

There are two issues I wish to emphasize in particular this morning. First, our 

principal concern is not the probability of triggering large earthquakes. Large faults 

are required to produce large earthquakes. We assume that such faults would be 

detected, and thus avoided, by careful site characterization studies. Our concern is 

that even small-to-moderate size earthquakes would threaten the seal integrity of 

the formations being used to store CO2 for long periods without leakage. Studies by 

other scientists have shown that a leak rate from underground CO2 storage reservoirs of less than 1% per thousand years is required for CCS to achieve the same 

climate benefits as switching to renewable energy sources. 

Second, it is important to emphasize that we recognize that CCS can be a valuable and useful tool for reducing greenhouse gas emissions in specific situations. 

Our concern is whether CCS can be a viable strategy for achieving appreciable global greenhouse gas reductions. From a global perspective, if large-scale CCS is to significantly contribute to reducing the accumulation of greenhouse gases, it must operate at a massive scale, on the order of 3.5 billion tonnes of CO2 per year. This 

corresponds to a volume roughly equivalent to the 627 billion barrels of oil currently 

produced annually around the world. 

Multiple lines of evidence indicate that pre-existing faults found in brittle rocks 

almost everywhere in the earth’s crust are close to frictional failure, often in response to small increases in pore pressure. In fact, over time-periods of just a few 

decades, modern seismic networks have shown that earthquakes occur nearly everywhere in continental interiors. In light of the risk posed to a CO2 repository by even 

small-to-moderate size earthquakes, formations suitable for large-scale injection of 

CO2 must be well-sealed by impermeable overlaying strata, weakly cemented (so as 

not to fail through brittle faulting) and porous, permeable, and laterally extensive 

to accommodate large volumes of CO2with minimal pressure increases. 

Thus, the issue is not whether CO2 can be safely stored at a given site, the issue 

is whether the capacity exists for sufficient volumes of CO2 to be stored in geologic 

formations for it to have a beneficial affect on climate change. In this context, it 

must be recognized that large scale CCS will be an extremely expensive and risky 

strategy for achieving significant reductions in greenhouse gas emissions. 

Mr. Chairman, Senator Murkowski and members of the committee, thank you for 

the opportunity to speak to you today. 

The CHAIRMAN. Thank you all very much for the excellent testimony. Let me start with a few questions. 

Dr. Hitzman, I’m trying to get clearly in mind the main thrust 

of your conclusions. From what I believe I heard you say and have 

read in your report here, the 2 biggest potential causes of this seismic activity, human causes, would be injection of waste water 

which is a significant issue because there’s a lot of it injected. 

Second, if in fact we were to pursue carbon capture and storage 

at a large scale that also would be significant. 

That those 2 types of injection pose a much greater threat and 

are a much greater issue, in your mind, then the injection that is 

generally referred to as fracking and geothermal activity as well as 

I understand it. Is that a reasonable summary of your—— 

Mr. HITZMAN. That’s a very fair statement of what the report 

says. Yes. 
38 

The CHAIRMAN. So you’re not as worried about fracking. You’re 

not as worried about geothermal energy production activities. 

But you are worried about waste water and you are worried 

about CCS if it goes to a large scale? 

Mr. HITZMAN. Correct. It really is volume dependent. 

So in geothermal we’re trying to balance a reservoir. 

In fracking there’s very small volume. 

But in waste water, most of the waste water disposal wells are 

fine. But with vast numbers of them and putting lots and lots of 

these wells in, some of them with fairly large volumes, occasionally 

there will be an event. 

CCS, because it has such very large volumes, as pointed out by 

Dr. Zoback, are sort of in a different league. So that clearly is of 

concern. 

The CHAIRMAN. Now as far as I understand, to deal with the— 

or to reduce the likelihood that you’re going to have human felt induced seismic activity from waste water injection. I think your suggestion is that there are some best practices that can be followed. 

I guess my question there is, is it clear that who would have the 

responsibility or authority to define those best practices and try to 

implement them or is this such—you’ve got so many agencies and 

so many different levels of government involved here that the 

whole thing is a hodgepodge? 

Mr. HITZMAN. The committee actually didn’t try to specify who 

should do it because, as you say, there are a number of agencies 

and different groups involved. But clearly, sort of as happened with 

the DOE protocol for EGS. What took place there was a cooperative 

venture between several levels of government with academia, with 

industry, with local communities try and come up with best practices. 

The committee felt that that was the sort of way moving forward 

with the other energy technologies as well. 

The CHAIRMAN. So the Department of Energy or EPA or somebody at the Federal level could convene a group of all the various 

players in this field and try to come up with some kind of guidelines. Say this is what we need to be doing in order to reduce the 

likelihood of this seismic activity resulting from waste water injection. 

Mr. HITZMAN. Yes, absolutely. 

The CHAIRMAN. Yes. 

Now what’s your reaction to Dr. Zoback’s comment? 

He’s made a very interesting point here which is basically that 

he thinks that, as I understand it, and Dr. Zoback correct me if I 

misstate your view here. But your basic view is that in order for 

carbon capture and storage to be pursued on the large scale that 

it would have to be pursued in order to achieve significant climate 

change benefits or, you know, we have real problems in pursuing 

it at that scale considering the likelihood of leakage out of these 

underground storage facilities. 

Is that a fair summary of—maybe you can state it much better 

than that. 

Mr. ZOBACK. I’ll try. 

When we look at the global greenhouse gas problem, you know, 

the real problem is that by mid-century the—if we do nothing emis-
39 

sions will be twice as much as they are today. So we’ll be adding, 

you know, something like 15 billion tons of carbon to the atmosphere per year in 2050. You know, we’re currently at the 7 or 8 

billion ton level. 

So we have a problem that’s on the scale of needing to reduce 

emissions by 7 or 8 billion tons of carbon. Now if CCS is going to 

be part of that solution at that scale it has been proposed that it 

should deal with say, one seventh or one eighth of the problem. 

Can it go along with, you know, enhanced use of renewables? 

Can it go along with energy efficiency programs? 

Can it go along with fuel switching from coal to natural gas? 

All of which will reduce emissions. 

If it’s going to be a player at the billion ton level then we get 

into a situation where we need 3,500 projects of the scale of the 

single operable project that’s going on now in the North Sea. So it’s 

really not the fact that we can’t find good places to put CCS. But 

for CCS to be part of a global strategy for stabilizing emissions it’s 

got to operate at this billion ton of carbon scale which is 3,500 

times what we’re doing today at a single site. 

The CHAIRMAN. OK. 

Why don’t I defer to Senator Murkowski for her questions and 

then Senator Landrieu? 

Senator MURKOWSKI. Thank you, Mr. Chairman. 

I appreciate the testimony from all the witnesses this morning. 

Very interesting. I think that the focus here on CCS and waste 

water injection is an interesting one. Perhaps the results of this 

study were different than what some imagined before you began 

this. 

But let me ask the question again, sticking with the CCS. I mean 

we’ve got new EPA rules that essentially ban construction of new 

coal fired power plants unless CCS is out there. So a lot of interest 

in whether or not we can do this right and/or if at all. 

More specific perhaps to this committee is the work that we’ve 

done to draft the liability protections for CCS operators. So I guess 

the question to you, Dr. Hitzman, is with this information that we 

know have do you think that it is perhaps premature or even unwise to provide liability protection for CCS operators? I mean, can 

we even do this or do we need to know more? 

Mr. HITZMAN. That certainly is outside the scope of what our 

committee looked at. We did not look at insurance whatsoever. So 

where we can down to is that there is significant concerns. We 

thought that DOE should address those concerns to look at how 

this technology may play out in the large scales that Dr. Zoback 

has talked about. 

Senator MURKOWSKI. You—we’re talking now about the increased risk, comparative, when we’re talking about geothermal or 

fracking as it relates to waste water injection and CCS. But is it— 

it’s not fair to describe that the risk or the consequences between 

waste water injection and CCS are comparable. Is that correct? 

I mean, you’ve got a higher risk with CCS? 

Mr. HITZMAN. It depends on the volumes. So it’s volume related. 

If we were injecting billions of tons, as Dr. Zoback discussed, then 

the risks are probably much greater because certainly none of our 

waste water wells are injecting anywhere near that. 
40 

So really it’s—think about volume. The more volume probably 

the more risk. 

Senator MURKOWSKI. You made a statement that, let’s see, no 

geologic review before injection. This is with the disposal of the 

waste water. Is that, perhaps, part of the reason that we see higher 

rates of seismic activity is because you don’t have that same geologic study that you have, say for instance, when you’re doing a 

geothermal well or even fracking? 

You’ve got some pretty serious studies that proceed before you 

move forward. Is that perhaps accounting for some of the difference? 

Mr. HITZMAN. That’s part of it, yes. With any of the CCS projects 

going on, with certainly with geothermal, we have a lot of geologic 

data before those happen. 

For many waste water wells they’re relatively low cost operations. They don’t have a lot of citing—site characterizations done 

ahead of time. 

But it also is important to note that the vast majority of waste 

water wells do not have an issue. So we’re not, in the report, we 

certainly do not suggest requiring that that occur for all waste 

water wells. 

Senator MURKOWSKI. OK. 

Dr. Leith, let me ask you about monitoring. Both the report and 

your testimony indicate that we need greater monitoring activity. 

In terms of scale do we need to double the monitoring that we’re 

doing? 

What would you suggest in terms of stepped up monitoring activities here? 

Mr. LEITH. The USGS, the National Seismic Network, is capable 

of routinely locating earthquakes that are around magnitude 3 and 

in many areas lower than that. But with that network we certainly 

cannot detect the onset of low magnitude induced earthquakes 

from an injection operation in most of the country. 

So what we rely upon is learning early about the occurrence of 

earthquakes. That typically doesn’t happen until they’re felt. It’s 

just going to be above magnitude two somewhere. 

Then deploying portable seismometers to go in and assess what’s 

going on. This is what we did in Arkansas and in Oklahoma 

and—— 

Senator MURKOWSKI. Do you do that just in a few specific areas 

or is—are you doing this monitoring across the country? 

Mr. LEITH. We do not have enough portable systems to deploy to 

all of the interesting cases of induced seismicity. 

Senator MURKOWSKI. If you have enough portable systems in 

these interesting areas, as you put it, what would that require? 

Mr. LEITH. We have been so busy with natural earthquakes for 

the last few years. Then this increased occurrence of induced earthquakes has piled onto that demand. 

We would need, I would estimate, some hundreds of portable systems to respond to just the earthquakes that are in the magnitude 

4 and above range. That, of course, doesn’t include the scientist’s 

time, the analyst to evaluate the data and the researchers to then 

correlate what’s recorded by the seismometer to determine its rela-
41 

tion to the injection activity, the fluid volumes injected, the pressures and those sort of things. 

Senator MURKOWSKI. Thank you, Mr. Chairman. 

The CHAIRMAN. Senator Landrieu. 

Senator LANDRIEU. Thank you very much. I have a short statement for the record. 

Senator LANDRIEU. I want to say I really appreciate the hearing 

the chairman and the ranking member have put together. This is 

very, very interesting, particularly about the volume necessary, the 

3,500 sites, to take care of the billion tons of carbon sequestration. 

Let me ask you, if you could, Dr. Zoback, to describe these locations to the best of your ability to those of us that are trying to 

get our heads around what such a location might look like. You 

said there would need to be 3,500 sites. So we could pick 100 countries, put 35 in each one. 

How—what would a site look like? Describe the one that exists 

now so we can get a little better understanding of that. 

Mr. ZOBACK. The project that exists now is a gas field. It’s operating in the North Sea. When they produce the gas it has a large 

fraction of CO2 mixed with the methane. So they have to deal with 

the CO2. They separate it from the natural gas. Put the natural gas into 

a pipeline. Then they have an injection well in which they inject 

the CO2 into a geologic formation, basically above the gas reservoir. 

This geologic formation has, what I consider to be, you know, ideal 

characteristics. 

First, it’s very laterally extensive. It’s big. So you’re putting the 

CO2 into a large volume. 

Senator LANDRIEU. It’s right near the site itself. 

Mr. ZOBACK. That’s exactly right. It’s—the well has been drilled 

off the same platform that the gas wells were drilled from. 

So the geologic formation, it’s called the Utsira formation. It’s a 

very—it’s laterally extensive. It’s very porous and permeable so it’s 

easy for them to get the CO2 into it. It has this added characteristic that it’s very weak and friable. 

It’s easy to imagine that if you had a very weak sandstone and 

you squeezed on it, well it would just kind of deform slowly in your 

hands and, you know, there’s no problem. Whereas a very strong 

rock, as you squeeze on it, it holds the force much better. But when 

it does fail it will fail brittle-ly. You know, it’s like a very small 

earthquake. 

So the Utsira formation is porous, permeable, laterally extensive 

and very weak and located where you want it to be. It’s absolutely 

ideal. 

Senator LANDRIEU. Let me follow that up. Because I was thinking that it would have to be on countries, on land. But this could 

be 3,500 sites in the world in the oceans, on land, etcetera, 

etcetera. 

So while it sounds like a lot of sites, you know, it’s a big planet. 

So I think we have to get the scale of this to understand. But I 

think it’s a very important point that you raised. 

But it’s also, I would say in response, while it seems overwhelming when you first say it. Until you’ve had a little bit more 

information about how many other potentially, really enormous 
42 

and very good sites there might be. Before we completely rule this 

out we need to have a little bit more, a lot more, data about that. 

Let me ask my other question. 

I’m very pleased to hear that fracking is not the problem. We’ve 

heard a lot of problems about fracking. Since my State is doing a 

lot of it and think we’re contributing to the natural gas production 

which is helping clean our atmosphere and provide the energy that 

our Nation and the world needs to move forward. But it’s the waste 

water injections. 

So I want to ask a couple of questions. 

Is the oil and gas industry, primarily in the United States, responsible for the majority of waste water wells? Are there other industries that are injecting waste water? Could somebody give us 

some data, if you have it, about that? 

Is it primarily the oil and gas industry or is it primarily other 

mining or is it petrochemical or agriculture, etcetera, etcetera? 

Mr. HITZMAN. There’s some data in the NRC report. I don’t have 

at the top of my head the percentage. But there are a number of 

producers of waste water that are disposed in the subsurface. Oil 

and gas is one of the major ones in the country. 

Senator LANDRIEU. But there are other major ones? 

Mr. HITZMAN. There are other major ones. 

Senator LANDRIEU. Are there any industries that are more than 

the oil and gas industry? Does anybody know? You think there 

would be—— 

Mr. HITZMAN. I think it probably is the single largest. But it’s 

probably not super high above. 

Senator LANDRIEU. Above the others. 

Mr. HITZMAN. Some of the others, yes. 

Senator LANDRIEU. OK. 

Those are my questions. Thank you. I’m going to submit the rest 

for the record. 

The CHAIRMAN. Thank you very much. 

Let me just try to put a little finer point on Dr. Zoback’s testimony and as least as I understand it just to be clear. As I understand, your basic point is that you doubt that CCS, carbon capture 

and storage, can be a successful strategy for dealing with the long 

term effects of climate change. A main reason you doubt that is because of these small to moderate sized earthquakes that, not only 

do you have to have 3,500 of these projects like the one you’ve just 

described to us. 

But there are small to moderate size earthquakes that occur naturally, as I understand it, that will, as you put it, threaten the seal 

integrity of the formations that might be used for the CCS. Is that 

accurate? 

Mr. ZOBACK. That’s exactly our point, Senator. 

The CHAIRMAN. Yes. Alright. 

Is this something you and fellow researcher expert that you mentioned have concluded on your own? Is this anything that the—any 

other group has looked at? Has the National Academy reviewed 

that set of recommendations or conclusions? 

Mr. ZOBACK. Basically the conclusions we’ve recently written 

about are essentially identical to the conclusions that the com-
43 

mittee, chaired by Professor Hitzman, came to. So we’re in complete concordance. They basically said—— 

The CHAIRMAN. But their report, the one that we have before us 

today doesn’t go as far as you’re going with your conclusions about 

the problems with planning on CCS as a strategy for long term climate change mitigation. 

Mr. ZOBACK. That’s true. They did not go that far. But in some 

ways they went further by pointing out the potential for large 

earthquakes because of the extremely large volumes to be injected. 

The question there is how good site characterization studies will 

be. We took what we thought was an approach by saying the site 

characterization will be so comprehensive that, you know, there 

will be no big faults. There will be no probability for a bigger earthquake. But it’s the small faults that you can miss. 

So therefore, our statement would have been due to the large 

scale, large volumes, there’s a high probability of something happening, probably something small to moderate in size. Their statement was a bit stronger on the hazard part of it. They said that 

in fact there was the potential, perhaps, of missing some of the bigger faults and a potential for a larger earthquake occurring. 

So philosophically I think we’re 100 percent in agreement. It’s a 

slight change in interpretation about what the hazard might be. 

The CHAIRMAN. Dr. Hitzman, let me just ask you. 

Did you—does your report deal with the issue of whether or not 

small earthquakes or small instances of induced seismicity might 

result in natural earthquakes being substantially more likely in 

certain areas? For example if you go to a place where there’s a natural known fault and there’s a real risk of an earthquake at some 

point, could you hasten the time of that earthquake or increase the 

likelihood of that natural major earthquake by doing the type of 

small injection activity that we’re talking about here? 

Mr. HITZMAN. That is addressed in the report. The basic answer 

is yes that many faults are near a critical state. So if we perturb 

them, manmade, we can trigger events. So the answer is yes. 

Is that something we routinely do? No. I mean site characterization, especially around areas of known faults we do today. 

So I don’t see that as a particular large issue. 

The CHAIRMAN. So as long as we stay away from the known 

faults that are naturally there, we pretty much deal with that 

problem. 

Mr. HITZMAN. Right. But what happens is there are faults we 

don’t know about. That’s where, certainly in the waste water injection, that’s where we’ve had the problems. We found faults we 

didn’t know existed. 

The CHAIRMAN. Senator Murkowski. 

Senator MURKOWSKI. Thank you, Mr. Chairman. 

I want to follow up to the questioning that Senator Landrieu had 

about the various types of waste water injection. It’s my understanding that there are 6 different classes of injection wells. 

One is municipal and industrial waste. We’ve got mineral solution, mining. We’ve got other things. 

So the question would be whether or not we think that any of 

these other well classifications. Whether or not they’ve been associ-
44 

ated with any additional seismic activity, whether we’ve looked at 

that. Whether it’s possible that they could. 

Then as a follow on as we see communities expanding and population going into certain areas, is it possible that we could see enhanced seismic activity just due to what we’re contributing from 

the municipal and industrial waste? I don’t know whether it’s a significant enough volume or quantity to make a difference. Have you 

looked at that? 

Mr. HITZMAN. Our committee specifically looked at Class Two 

wells with energy injection. 

Senator MURKOWSKI. OK. 

Mr. HITZMAN. So we didn’t consider the others. 

But what I would say is it really makes no difference whether 

the fluid is produced by an energy or by another industry or just 

simply waste water. It’s water being injected down. 

Senator MURKOWSKI. It’s the volumes that are the critical piece. 

Mr. HITZMAN. Right. Right. 

So as we inject more and more volume into the subsurface, we 

probably will have more and more potential for seismic events. 

Senator MURKOWSKI. OK. Alright. 

Ms. Petty, we’ve been quiet regarding geothermal here. I am a 

huge advocate of geothermal power and the resource itself. We’ve 

got, I think, some considerable opportunities in my State. We’ve 

also got some pretty impressive fault lines that run up there have 

had a history of earthquake activity. 

We’ve apparently managed to avoid any major issues. I think 

that that’s great. But in listening to your testimony you seem to 

indicate that the risks associated with geothermal are perhaps 

more minimal. 

I guess a very generic question is whether or not you think the 

benefits then of geothermal outweigh any potential risk associated. 

Ms. PETTY. I think that the main aspect of this, as Dr. Hitzman 

said, is that in geothermal we want to balance the injection and 

production so that we don’t have a disproportionate amount of either. That way the pore pressure doesn’t change. There have been 

some cases in geothermal fields where we didn’t do that, where we 

took out more than we put back in. 

In those cases, especially when we started to put more in we’ve 

had increased amounts of seismicity. I think it’s that balancing of 

injection and production that’s kind of inherent to doing a good job 

of managing geothermal that makes me feel that we have less of 

an issue for potential large scale, induced seismicity, felt induced 

seismicity in geothermal. 

The cases where we are near large faults, I mean, in fact there 

are a number of geothermal fields that are near or actively injecting into faults. But because they add balance to the injection and 

production there hasn’t been an issue. 

For EGS where we are creating a reservoir, we—a necessity 

when we start out, we inject more than we produce because we 

don’t produce anything until we make the reservoir. That’s when 

the risk is more clear to us. In that’s where we need to have some 

kind of mitigation protocol. We have to have good site characterization, so that we can get that big resource. 
45 

Senator MURKOWSKI. It sounds like so much of this is, is we are 

learning. That’s an important piece to recognize in all of this as 

well. 

Dr. Zoback, you mention that there are ways that we can manage the risk. You cited 4 different points. 

I mean, one, which is pretty obvious, is avoid the faults. So we 

need to know where we are and we need to better understand our 

geology. Pay attention to that I would think. 

But appreciating that we can manage risk is one thing. Is there 

any way to avoid it to the extent that you can tell people don’t 

worry? We know and we understand what it is that we have to do 

to balance this. There should be no cause for concern. 

Are we to that point? 

Mr. ZOBACK. In some cases. For example thorough site characterization is a basis for assuring the public that you’ve done due diligence before you start. 

Monitoring with enhanced seismic networks if you think you’re 

in an area where something might happen. You know, you’re on 

top of it. That’s another issue that should assure the public. 

But something else is happening that should be pointed out with 

respect to the shale gas development and waste water injection 

problem. That is in the Northeastern U.S. which is, you know, an 

area of active development with the Marcellus shale is being exploited. There are really no good places to inject the waste water. 

So what’s happening is that industry has largely started to recycle the waste water. So the water that comes back from hydraulic 

fracturing is now being reused in subsequent hydraulic fracturing 

operations. That’s beneficial for everyone. 

You use less water. So the water resources are protected. You basically put the contaminated water, which was contaminated by its 

interaction with the shale to begin with. You put it back into the 

shale. 

So the more you can recycle these flow back waters, the smaller 

you make the problem. In the Northeastern U.S. this is now standard practice. In other areas, if there’s difficulty finding, you know, 

safe injectionsites, that practice can be extended to other parts of 

the country. 

Senator MURKOWSKI. We were in West Virginia this weekend 

looking at—we were at the Marcellus. They were speaking exactly 

to that process of the recycling and how that all plays into it. Again 

a recognition that we’re learning a little bit more. 

Did you learn anything from this report that you found surprising? 

Mr. ZOBACK. It was really nice to see that the information compiled, as it was. I was aware of the general issues, but they did a 

terrific job of pulling together information on a global basis and of 

course, with the United States getting particular emphasis. 

The other thing I really appreciated out of the report was that 

it points to the need for data. So often we’re asked, well, was that 

earthquake triggered or not. You don’t have a baseline to make an 

answer to that question. 

Whether it’s a seismic baseline and you’re not aware of what the 

seismicity was prior to a larger event occurring or the pore pressure or the stress or the pre-existing faults. In both the Youngs-
46 

town and Guy, Arkansas cases scientists have come forward after 

the fact and said, oh yeah, there was an active fault right there 

that was being injected into. Had that data been available prior to 

the injection neither incident would have occurred. 

So, you know, in some ways, as the report illustrates in case 

after case we have a good conceptual understanding of what the 

issues are but we rarely have the data in order to use that conceptual understanding to be definitive about, you know, what’s happened and how to prevent things from happening in the future. So 

it’s a data issue as much as anything else. 

Senator MURKOWSKI. Thank you all. I appreciate your testimony 

this morning. 

Thank you, Mr. Chairman. 

The CHAIRMAN. Thank you. 

Let me ask about a bill. Senator Murkowski referred to one of 

the bills that’s been reported out of our committee, S. 699, that provides—it proposes to provide some liability protection for CCS 

projects. The idea of that or the general thrust of it is to say that 

for the first ten large demonstrations of CCS there would be some 

liability protection provided if DOE could determine that there’s 

adequate measuring and monitoring and testing to verify that the 

carbon dioxide that is injected into the injection zone is not escaping or migrating and is not endangering underground drinking 

water sources. 

The idea of the legislation and then of course the bill tries to provide a long term stewardship for these demonstration projects, 

these first 10. I guess that I’d ask Dr. Hitzman. Is there anything 

in your report or in the work that your committee did that would 

tell us whether it makes sense to proceed with these kinds of large 

demonstration projects or to have encouragement to industry to 

proceed with these or not? 

I mean, is this something that is a waste of effort or is it something that would make some sense to help us understand whether 

or not this is an avenue that’s going to be beneficial? 

Mr. HITZMAN. I think what the report says is that we also see 

the potential benefits of doing CCS. But that we really need to understand it better at the scales that are being projected. So I’m not 

sure exactly how large, how many—what the volume is in these ten 

demonstration projects over the long term. 

But we recommend that the DOE continue with its research, 

probably use some of the research it’s doing now and focus it a little more on this particular issue so it can be better understood. 

That right now, we need the data. We can’t answer your question 

directly. 

The CHAIRMAN. OK. 

Dr. Zoback, did you have thoughts as to whether it makes sense 

for the Department of Energy and the Federal Government to be 

encouraging some of these large scale demonstration projects 

through this kind of legislation or do you think it’s such a nonstarter as that we really should look elsewhere to solve the long 

term climate change issue. 

Mr. ZOBACK. The paper that we, my colleague and I, just published on this topic is published as a perspective piece. It really is 

our perspective that because of these potential problems one has to 
47 

consider this, the strategy of large scale CCS with these issues in 

mind. So what we’re trying to do—and by the way, the paper was 

published yesterday. So there’s going to be a lot of reaction to it 

without question. 

What we’re trying to do is just change the dialog and ask people 

to consider this question not just in the context of the scale and the 

cost which have been raised by many people in the past. They are 

very real issues. But also in the context if 10 or 20 years from now 

one of these moderate sized earthquakes occur in one of the repositories what is that going to mean for this strategy that we’ve, you 

know, we’ve embarked on. 

So this has to be thought through very carefully. I’m not familiar 

with the legislation you referred to. So I’d rather not comment on 

it. 

But we’re just trying to change the dialog and broaden people’s 

perspective just as the case that triggered seismicity is not considered in the licensing requirements for a Type Two waste water injection well. Perhaps it should be, at least in certain parts of the 

country. Triggered seismicity should certainly be a strong consideration as we look at CCS in a research mode in the future. 

The CHAIRMAN. But your concern is triggered seismicity. But 

you’re also—your concern is natural seismicity. You’re basically 

saying there are natural, small and medium sized earthquakes 

that may thwart our ability to use CCS at large scale to solve climate change problems long term. 

Mr. ZOBACK. That’s true, Senator. We’re—but by raising the pore 

pressure, you know, the probability of something happening goes 

up because you are basically advancing the time at which a natural 

event would have occurred anyway. So in a given area natural 

earthquakes occur but they might be so infrequent that you would 

assume that during the lifetime of the repository there’s no possibility of an event occurring. 

But by injecting fluid we sort of bring the faults closer to failure 

and therefore enhance that probability. 

The CHAIRMAN. Senator Murkowski, did you have additional 

questions? 

Thank you all very much. I think this has been very useful. 

Again, Dr. Hitzman, thank you for all the work you did on this 

report and your entire committee. 

That will conclude our hearing. 

[Whereupon, at 11:18 a.m. the hearing was adjourned.] 

(49) 

APPENDIX 

RESPONSES TO ADDITIONAL QUESTIONS

RESPONSES OF MURRAY W. HITZMAN TO QUESTIONS FROM SENATOR BINGAMAN

Question 1. Dr. Zoback has testified that the risk of venting stored carbon dioxide 

from small, induced seismic events is a primary concern and obstacle to the scaling 

up of CCS technologies to play a significant role in mitigating global greenhouse gas 

emissions to the atmosphere. Do you agree with this assessment? 

Answer. The statement of task for the study did not examine include consideration of the escape of carbon dioxide from CCS projects, thus we are not in a position to comment on this aspect of induced seismicity. 

Question 2. The NAS study we just heard about indicates that there have been 

relatively few induced seismic events that are directly attributable to the energy 

technologies considered here. At the same time, Dr. Leith’s testimony shows a sharp 

increase in the number of mid-continent earthquakes that USGS has measured over 

the past decade. 

Question 2a. Is there something else going on that could be causing this trend in 

earthquakes? 

Answer. The data Dr. Leith referred to in his testimony became available at the 

end of the NRC study and was not available in a peer-reviewed form. Hence, we 

were unable to examine it in detail. There could be a number of reasons for the seismicity to have apparently increased. Deep well disposal of waste water associated 

with energy development is one possibility. Another is a natural increase in seismicity. Finally, the apparent increase in number of events could be due to changes 

in the monitoring technologies employed over the past several years. 

Question 2b. Is this a measurement issue, or is it just that more work needs to 

be done to figure out what caused these earthquakes? 

Answer. As noted above, it could be a measurement issue. Certainly more work 

is required to better understand these seismic events. 

RESPONSES OF MURRAY W. HITZMAN TO QUESTIONS FROM SENATOR MURKOWSKI

Question 1. To the extent that wastewater injection wells are geologically unavailable in certain Eastern US areas, might those areas bear a correspondingly remote 

risk of induced seismicity from natural gas development? 

Answer. If the question is if waste water injection wells are not utilized will the 

seismic risks be decreased the answer is yes. However, fluids from energy development will need to be managed in some manner. 

Question 2. The NRC report indicates that the Federal and State Underground 

Injection Control (UIC) Programs ‘‘do[es] not address the issue of seismicity induced 

by underground injection.’’ At the same time, the current UIC program does require 

the injection well operator to perform a site characterization, including identifying 

the risks associated with nearby faults if any are located. Furthermore, several 

states (including Arkansas, Colorado, Ohio, and West Virginia,) are currently modifying their UIC Programs to specifically address seismicity. To this extent, might 

those state regimes reflect any of the proposed actions as noted in the report? 

Answer. The NRC report states ‘‘the Safe Drinking Water Act... does not specifically address the issue of seismicity induced by underground injection. (page 

106)’’ However, individual states have the authority to promulgate rules above and 

beyond the requirements of the SDWA including requirements such as providing additional information concerning induced seismicity as part of the permitting process. 

Our report (page 119) specifically notes the states of Colorado and Arkansas have 

adopted additional permitting regulations concerning induced seismicity in addition 

to the regulatory framework put forth in the SDWA. The additional information required by the state of Colorado closely parallels portions of the ‘‘Hazard Assessment’’ 

protocol recommended in our report on page 146. Our report also notes on page 106 
50 

‘‘UIC regulations requiring information on locating and describing faults in the area 

of a proposed disposal well are concerned with containment of the injected fluid, not 

the possibility of induced seismicity.’’ 

Question 3. The report establishes the ‘‘felt at surface’’ threshold as a magnitude 

2.0 seismic event. However, USGS documents state that a magnitude 2.0 to 2.9 is 

generally not felt, but might be recorded, while for the general population a magnitude 3.0 to 3.9 is more likely to be ‘‘felt.’’ As also noted, a seismic event typically 

does not cause damage until its magnitude falls in the range of 4.0 to 4.9, and the 

report indicates that the purpose of implementing a risk management protocol is to 

prevent the occurrence of damaging events. Are the report’s proposed actions targeted at such a risk management protocol or do they go further to seek to address 

any induced seismicity which might be recorded? 

Answer. While seismic events in the 2.0 range are commonly not felt, particularly 

if they occur deep within the Earth’s crust, the NRC committee met with residents 

living in the area of The Geysers where events in this range are shallow and are 

routinely felt. Damage from a seismic event depends on the location of the event 

relative to the structures being considered, the construction of such structures, and 

their contents. The NRC committee identified magnitude 2.0 since this is the smallest seismic event that can usually be felt by humans, even for shallow events caused 

by humans. The committee certainly is suggesting a risk protocol that is practical 

and widely applicable, not one for events that pose no risk. We would note that we 

are not disagreeing with the USGS documents, but feel the difference in wording 

has to do with the preciseness of the threshold of what may be felt. 

Question 4. Of the corresponding wells drilled for each of the following energy 

technologies in the U.S., please provide what percentage have been proven to induce 

seismicity: 

A) Enhanced oil recovery 

B) Wastewater injection wells 

C) Geothermal 

D) Hydraulic fracturing 

Answer. The committee could not find reliable statistics on the percentage of wells 

that have, or might have, induced felt seismicity (greater than M 2.0) for various 

energy technologies. Developing a reliable database of the numbers and characteristics of wells, and of the incidences of induced seismicity, as recommended in our report, will help with the understanding of the percentages associated with induced 

seismicity. 

However, based upon the available data from peer-reviewed resources the committee identified and examined, neither enhanced oil recovery nor hydraulic fracturing have to date have been proven to have induced felt seismic events in the 

United States. 

Regarding geothermal energy, although some of the events in our report’s database were clearly caused by injection to generate geothermal energy (for example 

at the Geysers and in the Coso geothermal field), geothermal wells tend to be drilled 

in areas that are often seismically active, making ‘proof’ of the tie to fluid injection 

difficult. 

Our report suggests that felt earthquakes at about 8 locations in the US over a 

period of about 40 years have been reasonably proven to be linked to wastewater 

injection. We know only the approximate number of wells today (∼30,000); some of 

the older wells that caused felt events are no longer in operation. An approximate 

estimate of the fraction of wastewater wells that have induced felt earthquakes is 

therefore 8/30,000, which is about 3/100 of 1%. 

Question 5. At the hearing, it was not clear how many of the various UIC wells 

of various classes were associated with oil and gas development (as opposed to municipal waste, etc.). Can you provide the committee with the breakdown of the various UIC well types and percentages relative to the total number of wells? 

Answer. The committee examined in detail only Class II wells, with some mention 

of Class V and Class VI (CCS) wells. The only Class VI wells currently in operation 

are those associated with two carbon sequestration test sites supported by the Department of Energy. Class II wells, of which there are approximately 151,000 currently permitted in the United States, are all used for the injection of fluids associated with oil and gas operations. Of that total of 151,000, approximately 30,000 

(∼20%) are for waste water disposal (from oil and gas development), approximately 

108,000 (∼71%) are for secondary oil and gas recovery (waterflooding), and approximately 13,000 (∼9%) are for tertiary recovery (enhanced oil recovery). Class V wells 

are the most numerous, accounting for almost 79 percent of the total number of UIC 

wells; wells used for fluid injection related to geothermal energy fall within this well 

class. However, only 239 wells in the United States among approximately 400,000- 
51 

650,000 Class V wells permitted in the country are for geothermal energy. The committee did not examine the other kinds of wells (which include storm water drainage 

wells, septic system leach fields, etc.) in this study so cannot provide a breakdown 

of the numbers of these kinds of wells. 

RESPONSE OF MARK D. ZOBACK TO QUESTION FROM SENATOR BINGAMAN

Question 1. Your testimony noted that offshore formations similar to the one utilized by the Sleipner project in Norway and also depleted oil and gas reservoirs 

could potentially be suitable for long-term storage of high volumes of carbon dioxide. 

The Department of Energy indicates there may be as much as 7.5 trillion tons of 

CO2 storage capacity in offshore formations in the Gulf Coast that are similar to 

the Sleipner project in Norway. The most recent estimates from the National Energy Technology Laboratory indicate that there may be as much as 20 billion tons 

of CO2 storage capacity in depleted oil and gas reservoirs. 

Question 1a. Could you please comment on these assessments of storage capacity 

and their suitability for the long-term storage of high volumes of carbon dioxide? 

Question 1b. Could you provide an estimate of how much storage is available in 

the types of formations that you described as having suitable characteristics for 

such long-term storage? 

Answer. As we noted in our PNAS paper on the potential of triggered seismicity 

associated with CO2 storage, there are a large number of formations in the Gulf 

Coast that have appropriate characteristics for long term CO2 storage. In other 

words, they are porous, permeable, weakly-cemented, laterally extensive, have adequate cap rocks and seals, etc. I am not familiar with the screening criterion used 

by the Dept. of Energy in their assessment of 7.5 trillion tons of CO2 storage capacity in these formations. If their criterion considered all of the characteristics enumerated above, it should be straightforward to calculate the rates at which CO2

could be injected without generating excess pore pressure could accommodate the 

enormous volumes of CO2 generated in the U.S. each year. Obviously, transport of 

large quantities of £ from thousands of point sources throughout the U.S. to the Gulf 

Coast would be a formidable operational challenge. Nonetheless, utilizing appropriate geologic formations in the Gulf Coast is a far more attractive strategy than 

utilization of non-ideal formations (from the perspective of possible earthquake triggering) that are located more closely to CO2 sources. With respect to the National Energy Technology Laboratory’s estimate that 20 billion tons of CO2 could be stored in depleted oil and gas reservoirs, it is important 

to recognize that this does not represent very much capacity. Coal burning power 

plants in the U.S. alone generate about 2 billion tons of CO2 each year so that depleted oil and gas reservoirs could accommodate emissions from coal burning plants 

for only 10 years. Another consideration is that successful long-term storage of CO2

in depleted reservoirs could be compromised by leakage through the cemented annulus of wells or via damaged well casings. Both are common occurrences in old wells. 

In addition, it is important to assure that oil field operations did not affect the natural geologic seals of the hydrocarbon reservoir. There are a variety of mechanisms 

could compromise the reservoir’s seal such as depletion-induced faulting or hydraulic fracturing, either when the well was first drilled or during subsequent water 

flooding operations. 

I have not carried out an assessment of the CO2 storage capacity of the geologic 

formations I would classify as being ideal for sequestration. Thus, I cannot respond 

to question 1b. 

RESPONSES OF MARK D. ZOBACK TO QUESTIONS FROM SENATOR MURKOWSKI

Question 1. To the extent that wastewater injection wells are geologically unavailable in certain Eastern US areas, might those areas bear a correspondingly remote 

risk of induced seismicity from natural gas development? 

Answer. It is true that there is a remote risk of triggering seismicity associated 

with multistage hydraulic fracturing in horizontal wells, the typical technique used 

to produce natural gas from shale formations. Any given hydraulic fracturing operation involves pressurization of small volumes of rock (typically a few hundred feet 

along the length of the wellbore) for short periods of time (typically about two 

hours). Hence, the probability of the pressurization affecting faults that might induce earthquakes large enough to be felt at the surface is extremely low. I fully 

agree with the conclusion of the NRC report that this is the principal reason why 

hundreds of thousands of hydraulic fracturing operations to develop gas from shale 

in the U.S. have not produced any confirmed cases of triggered seismicity. Globally, 

there has only been one confirmed case in which hydraulic fracturing associated 
52 

with shale gas development has triggered one very small earthquakes big enough 

to be felt at the surface. Considering the extremely small number of triggered earthquakes with hundreds of thousands of hydraulic fracturing operations clearly demonstrates that the risk associated with shale gas development is extremely low. 

Question 2. The NRC report indicates that the Federal and State Underground 

Injection Control (UIC) Programs ‘‘do[es] not address the issue of seismicity induced 

by underground injection.’’ At the same time, the current UIC program does require 

the injection well operator to perform a site characterization, including identifying 

the risks associated with nearby faults if any are located. Furthermore, several 

states (including Arkansas, Colorado, Ohio, and West Virginia,) are currently modifying their UIC Programs to specifically address seismicity. To this extent, might 

those state regimes reflect any of the proposed actions as noted in the report? 

Answer. It is good to learn that several states are modifying their UIC Programs 

to address the potential for triggered seismicity. If this has been in response to the 

NRC report, this is indeed a welcome development. 

RESPONSES OF WILLIAM LEITH TO QUESTIONS FROM SENATOR BINGAMAN

Question 1. Dr. Zoback has testified that the risk of venting stored carbon dioxide 

from small, induced seismic events is a primary concern and obstacle to the scaling 

up of CCS technologies to play a significant role in mitigating global greenhouse gas 

emissions to the atmosphere. Do you agree with this assessment? 

Answer. Dr. Zoback’s study identified the need to carefully study any prospective 

CCS projects and to evaluate potential risks associated with particular projects. We 

agree that induced earthquakes could be a significant risk to the efficacy of largescale CCS and that this hazard needs to be carefully studied and better understood. 

Although injection of CO2 into depleted oil and gas reservoirs (for example, as used 

in secondary oil recovery) may pose a low risk for induced seismicity, such is not 

the case during injection of CO2 into normally pressurized, undepleted aquifers. For 

injection in undepleted reservoirs, the geologic sequestration of CO2 is probably not 

significantly different from other large-volume liquid-injection projects, such as 

wastewater disposal at depth, for which there are numerous case histories involving 

earthquakes large enough to be of concern to the public. One of the early case histories concerned the injection of 625,000 cubic meters of wastewater at the Rocky 

Mountain Arsenal (RMA) well in the mid-1960s, which induced earthquakes of 

about magnitude 5 and caused damage to structures in the Denver, CO, area. 

Over the next three years, a DOE-sponsored demonstration project in Decatur, IL, 

will inject 1 million tons-about 1.4 million cubic meters of CO2- into an undepleted 

brine aquifer within the Mt. Simon sandstone at a depth of about 2 km. Injection 

at the Decatur well began in November 2011. Although the induced earthquakes at 

this site have been tiny as of July 2012, it is much too early to know what the seismic response will be as the injection grows; the total planned volume of injected CO2

at Decatur is more than double what was injected at the RMA. If the induced earthquake pattern at Decatur turns out to be similar to that at RMA, then some of the 

larger induced earthquakes that would occur at the site could indeed pose threats 

to the integrity of the capping seals. It is also possible that high pressures generated 

within the Mt. Simon sandstone could be communicated to ‘‘hidden’’ faults within 

the underlying granite basement. Although such faults have not been seen in the 

seismic data collected at Decatur so far, it is notoriously difficult to image faults 

in deep granitic rocks. Thus, a prudent approach would be to assume that there 

could be an earthquake risk to nearby communities during this project. 

To assess these seismic hazards, it is necessary to monitor induced earthquakes 

at each CCS pilot project with a seismic network designed to locate events precisely 

in three dimensions and thereby determine the exact nature of the seismic source. 

Microearthquake locations enabled by such a network would allow us to identify 

previously unknown faults within the underlying basement, as well as determine 

the maximum likely fault slip associated with these and other faults, including 

those located near the sealing formations. Other types of field and laboratory research will be needed to achieve a comprehensive understanding of the risk to reservoir seals from earthquake slip in various geological settings. 

Question 2. As USGS considers the amount of available storage for CCS, is the 

possibility of leakage from small seismic events something that is factored in? 

Answer. The 2007 Energy Independence and Security Act (Public Law 110-140, 

section 711) authorized the USGS to conduct a national assessment of geologic storage resources for carbon dioxide (CO2). The methodology that was developed for the 

national assessment (Brennan and others, 2010, http://pubs.usgs.gov/of/2010/1127/) 

addresses the geographical extent, the capacity, injectivity (permeability), and the 
53 

risk associated with potential storage formations. We evaluate the risk of a potential 

formation by providing maps of existing well penetrations which, in some cases, may 

be potential CO2 leakage pathways (for example well penetration maps see Covault 

and others, 2012, http://pubs.usgs.gov/of/2012/1024/a/). The USGS methodology also 

incorporates the Environmental Protection Agency (EPA) guidelines to prevent CO2

leakage to the surface and CO2 contamination of underground sources of drinking 

water (USDW) and overlying aquifers. EPA’s guidelines are: (1) a regional, well defined sealing unit to be present above each storage assessment unit, and (2) only 

assessing storage assessment units that have formation waters that are greater 

than 10,000 parts per million total dissolved solids. The risk of induced seismicity 

associated with a particular CO2 storage project depends on local storage reservoir 

fluid pressure management and CO2 injection rates and volumes, and is, therefore, 

an engineering problem that is not specifically evaluated in the current USGS CO2

storage assessment efforts. We do, however, note that a potential storage formation 

may be located in a region of the country where natural seismic risks are more likely. We are incorporating a discussion of the proximity of a potential storage formation to seismically active areas in the geologic framework reports for each assessed 

area that will be published during the coming year. 

Question 3. Dr. Zoback’s testimony noted that offshore formations similar to the 

one utilized by the Sleipner project in Norway and also depleted oil and gas reservoirs could potentially be suitable for long-term storage of high volumes of carbon 

dioxide. The Department of Energy indicates there may be as much as 7.5 trillion 

tons of CO2 storage capacity in offshore formations in the Gulf Coast that are similar to the Sleipner project in Norway. The most recent estimates from the National 

Energy Technology Laboratory indicate that there may be as much as 20 billion tons 

of CO2 storage capacity in depleted oil and gas reservoirs. 

Question 3a. Could you please comment on these assessments of storage capacity 

and their suitability for the long-term storage of high volumes of carbon dioxide? 

Question 3b. Could you provide an estimate of how much storage is available in 

the types of formations that Dr. Zoback has described as having suitable characteristics for such long-term storage? 

Answer a. The North American Carbon Storage Atlas (2012, available at: http:// 

www.netl.doe.gov/technologies/carbonlseq/global/nacap.html), published jointly by 

the Department of Energy and representative agencies from the governments of 

Canada and Mexico, indicates that within the Atlantic, Gulf of Mexico, and Pacific 

offshore regions of the United States, there is an estimated range of 467 billion to 

6.4 trillion metric tons of potential CO2 storage capacity in saline formations. The 

North American Storage Atlas also reports that oil and gas reservoir CO2 storage 

resources for the United States (onshore and offshore) are approximately 124 billion 

metric tons. In addition, a report by Kuuskraa and others (2011, http:// 

www.netl.doe.gov/energy-analyses/pubs/storing percent20co2 percent20w 

percent20eorlfinal.pdf), that was prepared for the National Energy Technology 

Laboratory, indicates that nearly 20 billion metric tons of CO2 may be needed to 

economically produce oil using ‘‘Next Generation’’ enhanced-oil-recovery techniques 

utilizing a mixture of naturally occurring CO2 produced from CO2-rich underground 

reservoirs and CO2 from anthropogenic sources. The resource numbers reported by 

the North American Carbon Storage Atlas (2012), the Carbon Sequestration Atlas 

of the United States and Canada (NETL, 2010, http://www.netl.doe.gov/technologies/ 

carbonlseq/natcarb/index.html), and Kuuskraa and others (2011) are general estimates of potential geologic CO2 storage resources in various regions of North America and the United States. 

The USGS is currently working on a comprehensive assessment of onshore areas 

and State waters that will identify and evaluate the Nation’s potential CO2 storage 

resources. Data used in the previous DOE assessments and data provided by State 

geological surveys are being integrated with USGS data to conduct these assessments. The USGS typically does not assess Federal offshore U.S. resources and refers to or works with the Bureau of Ocean Energy Management (BOEM) when evaluating offshore resources. By 2013, the USGS Geologic CO2 Sequestration Assessment Project will have geologically characterized and assessed more than 200 potential storage formations in 37 basins across the United States. This assessment will 

be the most comprehensive accounting of the Nation’s CO2 storage potential ever 

completed, and provide quantitative, probabilistic estimates of resource storage potential. A summary report is in preparation that will provide the storage assessment 

results for the Nation. In addition, the Geologic CO2 Sequestration Project is building an assessment methodology and associated engineering database that can be 

used for a detailed national assessment of recoverable hydrocarbon resources associated with CO2 injection and sequestration. USGS assessments are impartial, robust, 

statistically sound, and widely cited in the scientific literature and public media. 
54 

Answer b. The USGS assessment of CO2 storage capacities of onshore areas and 

State waters of the United States is scheduled to be completed in 2013. We do not 

have resource estimates available at this time. As mentioned in the answer for question 2 above, the risk of induced seismicity associated with a particular CO2 storage 

project depends on local storage reservoir fluid pressure management and CO2 injection rates and volumes, and is, therefore, a scientific and engineering problem that 

is not specifically evaluated in the current USGS CO2 storage assessment. The scope 

of research needed to better predict seismic risk in particular geologic settings is 

discussed further in the answer to question 1. In order to provide resource estimates 

for formations that are not likely to be prone to induced seismicity, an additional 

set of screening geologic and engineering criteria will need to be developed and applied to the assessment results generated by the current USGS Geologic CO2 Sequestration Assessment Project. 

Question 4. Is USGS doing, or planning to do work to better understand the risks 

of induced seismicity due to large-scale CCS as indicated in the report? Are there 

efforts at other agencies or national labs? 

Answer. The USGS is currently proposing to monitor induced seismicity at one 

or more DOE-funded CCS pilot projects, and we have been in contact with the operators of two such projects: one at Decatur, Illinois, and the other at Kevin Dome, 

northern Montana. Although no agreements have been reached so far, the USGS, 

as an objective science agency, is in a unique position to provide scientific knowledge 

needed to better understand and mitigate the potential seismic risk associated with 

CCS. In so doing, it is critical that these data and analyses be maintained in the 

public domain, to be amenable to full scientific peer review and to maintain public 

trust. 

The USGS recently purchased seismic recording equipment sufficient for a tenstation monitoring network that includes three seismometers that will record down 

boreholes about 500 feet deep. In the lower-noise environment at the bottom of these 

boreholes, we anticipate that the magnitude threshold for earthquake detection will 

be reduced considerably. 

The DOE-funded National Laboratories have conducted earthquake monitoring at 

CCS sites in Algeria and Australia, and perhaps other sites. In addition, the National Laboratories maintain an active and highly visible program in monitoring induced seismicity associated with Enhanced Geothermal Systems demonstration 

projects at several locations in the United States. 

The President’s budget request for fiscal year 2013 includes, as part of the hy- draulic fracturing initiative, a proposed $1.1 million increase to the Earthquake 

Hazards Program for work assessing the factors controlling the triggering of earthquakes due to fluid injection activities, developing a method to forecast the magnitude-frequency distributions of induced earthquakes including the maximum-magnitude earthquakes resulting from a specified fluid injection operation, and accounting in National Seismic Hazard Maps for the additional hazards due to fluid disposal-induced earthquakes. 

Question 5. The NAS study we heard about indicates that there have been relatively few induced seismic events that are directly attributable to the energy technologies considered here. At the same time, your testimony shows a sharp increase 

in the number of mid-continent earthquakes that USGS has measured over the past 

decade. 

Question 5a. Is there something else going on that could be causing this trend in 

earthquakes? 

Question 5b. Is this a measurement issue, or is it just that more work needs to 

be done to figure out what caused these earthquakes? 

Answer a. USGS believes that the increase in the number of magnitude 3 and 

larger earthquakes in the U.S. midcontinent is most probably caused by increased 

wastewater injection activities. The increase is most pronounced in Arkansas, along 

the Colorado-New Mexico border, and in Oklahoma. Earthquakes have also been 

noted in Texas, Ohio, and West Virginia, where they are otherwise uncommon. Research published since the NAS report was written demonstrates that the increase 

in earthquake activity in Arkansas is due to injection of wastewater related to shale 

gas development and production: http://srl.geoscienceworld.org/content/83/2/250. 

Studies recently completed by the USGS show that the earthquakes along the Colorado-New Mexico border are due to wastewater injection from coal-bed methane production in the Raton Basin. Studies to identify the underlying cause or causes of 

the increase in seismicity in Oklahoma are underway. 

Answer b. USGS is certain that the rate change discovered is not a measurement 

issue. Three lines of evidence support this conclusion. First, earthquakes with magnitudes of 3 and above (those used to detect the rate change) have been uniformly 

detected through the midcontinent since the 1970s by the USGS. Second, while im-
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provements in seismic instrumentation and installation of additional seismic stations have improved earthquake location accuracy, the algorithms for computing 

magnitude have remained unchanged. Third, both the USGS catalog and the catalog 

of the Oklahoma Geological Survey independently document the increase in activity 

that began in that state in 2009. 

To understand the factors that have led to the increased rate of induced earthquakes in the central and eastern United States, more work is clearly needed. Sitespecific investigations will be required to identify the underlying causes and improve our understanding so that the risk of induced earthquakes can be managed 

in the future. 

Æ