**[Summary of February 3-4 Meeting on Induced Seismicity Associated with
Enhanced Geothermal Systems.]{.underline}**

We would like to thank all that attended and participated in the
meeting, as well as the sponsors DOE/Geothermal and the IEA. In
addition, we would like to thank Roland Horn for providing the space at
Stanford and Steve Hickman for the space at the USGS. Last but certainly
not least we would like to thank Laura Gardner at Stanford for arranging
all of the logistics and wonderful food.

You should all be congratulated for the lively exchange of ideas and
presentations, it made the meeting a big success and created a momentum
to move forward in addressing this topic which is very important to the
success of geothermal energy.

Find attached the original invitation and purpose of the meeting for
reference, we of course took much longer than scheduled but all of the
objectives were met and we arrived at some solid paths forward.

Also attached is the list of contact information for all those who
attended the meeting ( the sign up list that was sent around) .

**[Summary of Workshop]{.underline}**

Allan Jelacic (DOE) and Chris Bromley (IGNS) opened the workshop by
stating that the motivation for the workshop was part of an
international program to pursue a collaborative effort to gather a
critical mass of expertise to assess the seismic risk from fluid
injection into enhanced geothermal systems (EGS). As stated in ANNEX I,
Environmental Impacts of Geothermal Development, Sub Task D, Seismic
Risk From Fluid Injection Into Enhanced Geothermal Systems of the
International Energy Agency (IEA) Geothermal Implementing Agreement:

"Participants will pursue a collaborative effort to address an issue of
significant concern to the acceptance of geothermal energy in general
but EGS in particular. The issue is the occurrence of significant
seismic events in conjunction with EGS reservoir development or
subsequent extraction of heat from underground. These events have been
large enough to be felt by populations living in the vicinity of current
geothermal development sites. The objective is to investigate these
events to obtain a better understanding of why they occur so that they
can either be avoided or mitigated. Understanding requires considerable
effort to assess and generate an appropriate source parameter model,
testing of the model, and then calculating the source parameters in
relation to the hydraulic injection history, stress field and the
geological background. An interaction between stress modeling, rock
mechanics and source parameter calculation is essential. Once the
mechanism of the events is understood, the injection process, the
creation of an engineered geothermal reservoir, or the extraction of
heat over a prolonged period may need to be modified to reduce or
eliminate the occurrence of large events."

In other words, if geothermal is to reach its full potential the issue
of induced seismicity must be addressed to the point of public
acceptance. It was very apparent that the key word in moving forward is
collaboration. Research, both applied and basic is going on at a variety
of sites around the world, creating data and results that have a high
potential of being synthesized such that key results and conclusions can
be more quickly and effectively derived. Some key questions and issues
pointed out were:

1.  [Is it possible to mitigate and optimise production at the same
    time?]{.underline} It was pointed out that some regard seismicity as
    a positive aspect of EGS. For example, microearthquake (MEQ)
    activity is a sign of enhanced fluid paths, fracture
    opening/movement and possibly permeability enhancement (especially
    in hydrofracture operations). On the other hand, will seismicity
    control the upper limit on production? Seismicity is a measure of
    how one is perturbing an already dynamic system and to estimate how
    fluid injection will perturb the system a good idea of stress
    distribution is necessary.

2.  [Does the reservoir reach an equilibrium?]{.underline} Steady state
    may be the wrong term, but energy can be released in many different
    ways. The steam/hot water is releasing energy as does the seismicity
    , creep, subsidence, etc. ( local and regional stress are the energy
    inputs or storage). It was pointed out that although the number
    events at The Geysers is increasing, the average energy release (as
    measured by cumulative magnitude of events) is actually constant or
    slightly decreasing. If this occurs by many small events then this
    is good, if it occurs by few big events then this is undesirable .
    Thus an understanding of magnitude distribution in both space and
    time is necessary.

3.  [What are the critical parameters necessary to estimate the
    seismicity hazard]{.underline}. Or more practically, what is the
    minimum knowledge necessary for estimating the seismic hazard. It
    was pointed out that the hazard will differ from site to site. For
    example, it was pointed out that at Soultz a magnitude 2.9 event
    upset the community and caused great concern about the operations.
    At the Geysers events of this magnitude occur every couple of
    months, although some of the local community members are not happy
    about this but if the seismicity was to stay at that level it would
    be generally acceptable. Also, if the field is sited in a remote
    area then there will be no community to feel the events.
    Additionally, if the geology is such that ground vibrations are
    minimized, i.e. hard rock versus infill, then the level of
    acceptable seismicity would be higher. In any case the definition of
    hazard will not be the same everywhere.

4.  [What are the factors controlling the seismicity?]{.underline} Apart
    from estimating the hazard there is a need to understand the physics
    of the process to not only mitigate but to gain knowledge on the
    short and long term impact of injections on production. Suggestions
    were made on factors which could influence the generation of seismic
    events , such as stress redistribution, (regional and local)
    geologic conditions and history, historical seismicity, faulting
    patterns and scale, reservoir pressure and temperatures, fluid
    content and distribution, geochemical conditions, production history
    ( rate of injection and withdrawal, pressures, volume of injection,
    etc.) spatial and temporal distribution of wells, and other factors
    that may contribute to the generation of small as well as large
    seismicity.

5.  [What measurements and data are lacking, and if additional data are
    needed, how much and how long should monitoring
    continue?]{.underline} It was pointed out that if one is to
    understand the physics of the process, dynamic range, bandwidth, and
    multicomponent seismic data are a great advantage. Also surface data
    versus borehole data should be taken into consideration as well as
    spatial and temporal aspects. An example was given on spatial
    coverage and source mechanism studies where it was pointed out that
    if one does have dense azimuthal coverage one can infer details of
    the failure mechanism and the type of energy release ( shear versus
    volumetric change, etc). Also, mentioned was the proper scale and
    range of reservoir parameters as mentioned above.

6.  [What can we learn from other induced seismicity cases]{.underline}?
    Several other instances of induced seismicity were presented and
    discussed. An oilfield example was presented where it was clear that
    the production caused seismicity, rather than injection. A mining
    example was also presented that showed volume change( subsidence?)
    caused seismicity. Triggered seismicity by distant events and
    teleseismic energy was shown to cause seismicity. However, triggered
    seismicity was not consistant with all events and the hypothesis was
    put forward that triggering was band limited and occured at lower
    frequencies.

7.  [In terms of larger seismic EGS events do they have a pattern with
    respect to the general seismicity?]{.underline} It was pointed out
    that at Soultz ,The Geysers and other sites the largest events occur
    on the fringes, even out side the "main cloud" of events. Why is
    this and what is the relation to the smaller events? Does this imply
    a stress redistribution larger than expected?

8.  [Can Probabilisitic Seismic Hazard Analysis (PSHA) be used for
    Geothermal areas to estimate the largest events]{.underline}? Most
    applications of PSHA is for "normal" tectonic areas where there has
    been a history of seismicity, known fault lengths and mechanisms and
    constant stress patterns over the time of interest. In geothermal
    regions none of these may be known. If one had tried to apply PSHA
    to The Geysers, the estimate would probably be way off of the
    reality. On the other hand, it was pointed out that there should be
    an effort to be responsible to the community to use some method to
    estimate the maximum event based on the best available data.
    Possibly comparing the potential EGS site to other similar sites ,
    historical seismicity in the area , etc could be used to place
    bounds on the larger events. Again it was pointed out that unless
    the physics is known it is difficult tro derive at accurate
    estimates of seismicity.

9.  [How does one explain the occurrence of large events when there are
    no large faults?]{.underline} The issue of stress drop versus fault
    size and moment was brought up. There is some evidence that large
    stress drops may be occurring on small faults resulting in larger
    magnitude events than the conventional models would predict. It was
    pointed out that stress heterogeneity may be a key to understanding
    EGS seismicity. Results were presented from Soultz that supports
    this hypothesis. For example the determination of the regional
    stress field is necessary before any stability analysis is done. It
    was also concluded that this requires integration of various
    techniques. It was also found that induced seismicity does not prove
    that the rock mass is close to failure, it only outlines local
    stress concentrations. It was also found that at Soultz it takes 4
    to 5 MPa pore pressure increments at around 3500m depth, to
    structure induced seismicity into a fresh large scale fault that
    ignores large scale pre-existing fractures. Lastly it is difficult
    to identify the failure criterion of large scale pre-existing
    faults, many of which do have a significant cohesion.

10. [Are there experiments that can be performed which will shed light
    on key mechanisms causing EGS seismicity?]{.underline} Over the
    years of observing geothermal induced seismicity, many different
    mechanisms have been proposed. Pore pressure increase, thermal
    stresses, volume change, chemical alteration, stress redistribution,
    subsidence, are just a few of the proposed mechanisms. ). Are
    repeating events a good sign or not, similarity of signals may
    provide clues to overall mechanisms. One proposed experiment was
    injecting hot water versus cold water to determine if thermal
    effects are the cause. If we can come up with a few key experiments
    to either eliminate or determine the relative effects of different
    mechanisms it would be a step forward.

11. [How does induced seismicity mitigation differ in natural fractured
    systems versus hydrofracturing environments?]{.underline} The
    variability of natural systems is quite large, they vary from system
    such as The Geysers to low temperature systems, each varying in
    geologic and structural complexity. Do similar mechanisms apply, how
    would one design mitigation measures for each, i.e will it be
    necessary to start new with each system or can we lean from each
    system such that it will be easier as we address each system.

12. 

# Path Forward

It was clear that we do not have all the answers and further work is
necessary. On the other hand, the operators pointed out that an open
ended research program may be scientifically interesting but how can we
get results in the short term that will answer the overall question that
the community and possibly regulators will ask of EGS, i.e what is the
risk?. Therefore, to meet the objective of the meeting, (how can
different efforts be leveraged to move forward) the following action
items were identified.

1.  Put the results of the meeting on a web site (which Chris Bromley
    said he would maintain) with the different presentations and other
    information people would think appropriate.

2.  The web site would also include links to data and results not
    presented at the workshop in order to facilitate data exchange.

3.  The web site would also serve as a means to facilitate researchers
    to work together and leverage individual research efforts.

4.  Form a working group to prioritize efforts and keep the
    collaboration current.

5.  Have a short and intermediate term goal of understanding mechanisms
    of larger "hazardous" events and develop mitigation techniques.

6.  Longer term goal of understanding induced seismicity in general.

7.  Publish summary of workshop in EOS.

8.  Have a dedicated issues of International Journal of Rock Mechanics
    addressing EGS Induced seismicity .

9.  Schedule the next workshop at the annual meeting of the GRC.

**[Attachment 1: Original invitation and agenda]{.underline}**

**[DOCUMENT FOR CIRCULATION TO POTENTIAL PARTICIPANTS]{.underline}**

> **[AT THE STANFORD MICROSEISMIC WORKSHOP]{.underline}**

Dear Colleagues,

As part of the interest and concern over induced seismicity in
geothermal systems we are organizing a workshop on seismicity caused by
enhancing geothermal systems. The workshop will be held directly
following the 2005 Stanford Geothermal Reservoir Engineering Meeting,
i.e. Thursday Feb 3, and until Friday about noon on Feb 4, 2005. The
location will be at the Hartley Conference center in the Mitchell Earth
Sciences Bldg.on the Stanford Campus the first day and at the USGS Bldg
15 the second day. You can get information on location and hotel
accommodations by logging on to the Stanford Geothermal Meeting website.
We have included the URL for accommodations at the Stanford SLAC House,
which is a new and very economical alternative to the nearby hotels.
<http://www.stanford.edu/dept/hds/SLAC/>. Information on the Sheraton is
also included. <http://ekofisk.stanford.edu/geoth/sheraton.html>

This workshop is a result of an IEA effort to address various issues
associated with geothermal systems. As the global demand for energy
increases it is obvious that geothermal must and will play a significant
part in meeting this demand. Exploitation of deep resources such as
Geothermal, mining, hydrocarbon etc. will need manipulation of the deep
geological setting to release the trapped economic resource. One of the
environmental as well as scientific issues that must be addressed is the
effect and role of seismicity in managing geothermal resources.
Seismicity is currently being used as a reservoir management tool, but
is it is also becoming a negative issue with some of the communities
surrounding geothermal fields. Events with magnitude 2 and above have
raised concern to the residents near certain fields for not only their
individual but cumulative effect. In particular, the general public\'s
perception is that this induced seismicity may cause damage to
structures on the surface, similar to that caused by "natural"
earthquakes. A related concern is that not enough resources have been
invested in trying to answer some of the questions associated with
larger induced events. For example, how and why do they occur and can we
devise any procedures to reduce them, what are the conditions that cause
a hazard to exist, etc.

A large amount of knowledge and experience exits and needs to be
synthesized. The objective of the workshop is to leverage resources and
knowledge to define a path forward. The workshop is intended to be an
interactive exercise with all contributing in one fashion or another,
i.e., a true workshop not a string of presentations. [In that sense,
participation will require a certain amount of preparation by all of the
attendees!!! Included in this invitation at the end is an agenda and
list of possible discussion topics. If you are willing to come and
participate we would also like to know in the areas where you would most
like to contribute to discussions, and, alternatively, if you think the
agenda is missing important topics , feel free to comment.]{.underline}
Ideally, the result of the workshop would define definite studies,
synthesis of information, and/or experiments that will shed light on the
cause and hopefully control of seismicity in geothermal systems.

Following is a suggested agenda and discussion topics. Feel free to
volunteer to be a discussion leader, which would entail a brief 5- 10
min introduction to the topic, keeping the discussion going, focusing on
what is known and what needs to done to answer key roadblocks.

A proposed agenda & possible chairpersons are shown below but this may
change depending on the response of the participants.

8:00 AM Introductions and welcome, Purpose and goals of workshop ,
anticipated results. ( Chris Bromley and Allan Jelacic)

8:15 AM Statement of Problem and Expected results of Workshop- Roy Baria

8:30 Discussion of Probabilistic Hazard Parameters - Art McGarr

9:00 Case histories/ description of bigger induced  events from various
sites and it\'s effect on general public Short ( 10 -- 15 min each)
Presentations on key observations and history of seismicity and
production. Available data, data coverage and possible opportunities,
instrumentation used, etc. The ultimate objective of these presentations
is to establish what do we know and what we need to study in the
future.\
**[\
]{.underline}**                        a.      Soultz          \
                        b.      The Geysers     **\
**                        c.      Indonesia  

Break 10:30 -- 10:45

                        d.      New Zeland                           \
                        g.      Others ( Oil and Gas)

Lunch 12:00

The afternoon topics are meant to follow the case histories and generate
discussion of possible mechanisms/reservoir processes/properties
controlling seismicity. For example, what are the key candidate
mechanisms for causing \"geothermal  events\", if there such a thing, is
it only injection  we need to control?, production?, how does the
natural fault and tectonic setting come into play ?, rock type? 
temperature, fault length and depth, geochemistry, etc. etc

1:00 PM Possible conditions which assist in the generation of bigger
seismic events such as: volume injected, specific stress conditions,
open system, closed system, injection flow and pressures, geological
setting etc. ( Mike Fehler Discussion Leader)

                                \
3:00 PM Break

3:15 PM Possible mechanisms for the generation of bigger induced events:
Dave Oppenheimer\
                        1. Shearing of large existing faults\
                        2. Possible stress migration and lock up\
                        3. Rupture velocity ie greater seismic
efficiency\
                        4. Stress relaxation\
                        5. etc.

5:00 PM adjourn

6:30 PM Dinner ( at the Hartly Center)

Day 2 ( to be held at The USGS in Menlo Park, Bldg 15,)

8:00 AM How is the seismic hazard estimated at any site & it\'s site
specific dependence

         Spatial & temporal distribution & it\'s effect on the hazard
potential\
         procedures for estimating / calculation of the seismic energy
form an event\
         Characterization of a seismic event using source parameters and
it\'s uncertainties\
         Characterization of a seismic event using FPS and it\'s
uncertainties

Quantitative relations between seismic energy release and injection
parameters

9:00 AM Public awareness & site investigation

Site investigation to minimise effect of seismic waves on the man made
structures.

Background investigation of possible problems for a specific site
(geology, stress)

Initial interaction with public to assess the acceptance of a programme.

Public relations exercise to make the project acceptable to the
community.

Establish a coordinating group to keep the local community in contact
with the programme.

10:00 AM Discussion and derivation of initial conclusions- Nafe Tokoz

A discussion about what  critical experiments and studies should be done
to advance our understandings.  Discussion on the cause of the bigger
events during fluid injections

Short and long term prospective to reduce bigger events. Where are the
gaps and what are the critical measurements that are needed to
understand and possibly mitigate seismicity. How do we interface with
the reservoir engineers and their understanding of reservoir mechanics.

12:00 Way forward & any other topics -Roy Baria

Cooperation under IEA/GIA & possible way forward\
           Exchange of data to verify possible conditions &
mechanisms                       

 Develop techniques to avoid bigger induced events and test\
           Develop  procedures to reduced the concern by the public

Possibly publish the summary of the workshop in an appropriate journal
(?)\
\
13:00 End of formal workshop

The workshop is jointly organized by Roy Baria ( EEIG Heat Mining, ie
the Soultz Project), Ernie Majer (LBNL, USA),Mike Fehler (LANL, USA);
Chris Bromley (GNS, New Zealand) and supported by Nafi Toksoz ( MIT,
USA)

**[Attachment 2: List of information on the attendees]{.underline}**

###  NAME E-MAIL PHONE ORGANIZATION

  ---------------- --------------------------------- -------------- ---------------
  Ernie Majer      elmajer@lbl.gov                   510/486-6709   LBNL

  Glenn Melosh     gmelosh@unocal.com                707/521-7721   Unocal

  Bill Cumming     wcumming@wcumming.com             707/546-1245   Cumming
                                                                    Geoscience

  Reinhard Jung    rjung@gga-hannover.de             0049           GGA Institute
                                                     511-6432820    

  Nicolas Cuenot   cuenot@eost.u-strasbg.fr          33 3 90 26 00  EOST,
                                                     70             University
                                                                    Strasboug

  Jean Charlety    charlety@eost.u-strasbg.fr        33 3 90 2400   EOST,
                                                     70             University
                                                                    Strasboug

  Chris Bromley    c.bromley@gns.crinz               64 7 37482 11  IGNS

  Jay Nathwani     jay.nathwani@go.doe.gov           303/275-4756   DOE-GO

  Ann              art@geothermex.com                510/527-9876   GeothermEx,
  Robertson-Tait                                                    Inc.

  Clement Baujard  clement.baujard@ensmp.fr          33 1 64 69 47  Paris School of
                                                     36             Mines

  Francois Henri   cornet@ipgp.jussieu.fr            33 1 44 27 38  Institute
  Cornet                                             97             Physics du
                                                                    Globe, Paris

  Piere Ungemach   piere.ungemach@geoproduction.fr   33 1 48 63 08  Geoprodction
                                                     08             Consultants
                                                                    (GPC)

  Paul Segall      Segall@Stanford.edu               650/725-7241   Stanford
                                                                    University

  Emily Brodsky    brodsky@css.ucla.edu              310/206-6256   UCLA

  David            oppen@usgs.gov                    650/329-4792   USGS
  Oppenheimer                                                       

  Lane Johnson     lnj@ccs.lbl.gov                   510/486-4173   LBNL

  Nafi Toksoz      Toksoz@mit.edu                    617/253-7852   MIT

  Sophie Michelet  sophiem@mit.edu                   617/253-7890   MIT

  Roy Baria        baria@soultz.net                  33 3 88 80 53  EEIG Soultz
                                                     63             

  Mike Fehler      fehler@lanl.gov                   505/667-1925   LANL

  Mitch Stark      mitchs@calpine.com                707/431-6101   Calpine Corp.

  Allan Jelacic    allan.jelacic@ee.doe.gov          202/586-6054   DOE

  John Garnish     john_garnish@yahoo.co.uk          44 1258 858684 

  David Wilson     david.wilson@mightyriver.co.nz    64 74 8570335  Mightyriver
                                                                    Power, New
                                                                    Zealand

  Miklos Antics    m.antics@geoproduction.fr         33 1 48 63 08  Geoproduction
                                                     08             Consultants
                                                                    (GPC)

  Steve Hickman    hickman@usgs.gov                  650/329-4807   USGS

  Dominque Bruel   dominque.bruel@ensmp.fr           33 1 64 69 47  ENSMP
                                                     54             

  Ali Khan         akhan@conservation.ca.gov         707/576-2385   DOOGR, State of
                                                                    California

  Nick Beeler      nbeeler@usgs.gov                  650/329-4863   USGS

  Ahmad Ghassemi   ahmad.ghassemi@und.nodak.edu      701/777-3213   University of
                                                                    North Dakota

  Volker Oye       volker@norsar.no                  47 63 805932   NORSAR

  Stephen Karner   karnsl@inel.gov                   208/526-6292   Idaho National
                                                                    Lab

  Susan Petty      blackmountaintech@earthlink.net   206/217-5960   Black Mountain
                                                                    Technology

  Evelyn Rueloffs  evelynr@usgs.gov                  360/993-8937   USGS

  Bob Creed        creedrj@id.doe.gov                208/526-9063   DOE

  Gillian Foulger  gfoulger@usgs.gov                 650/329-4143   University of
                                                                    Durham/USGS

  Bruce Julian     julian@usgs.gov                   650/329-4797   USGS

  Art McGarr       mcgarr@usgs.gov                   650/329-5645   USGS
  ---------------- --------------------------------- -------------- ---------------