Fluids and Faulting:

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Fluids and Faulting Water and Earthquakes in
California
Mark Zoback Stanford University
California Colloquium on Water October 12, 2004
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Earthquakes and Fluid Injection
Waste Injection Denver Arsenal
Fluid Injection Rangely Oil Field
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Coulomb Criterion Frictional Sliding
Sn
Coefficient of Friction
Pp
4
Earthquakes and Fluid Withdrawal
(after Segall, 1989)
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Earthquakes, Plate Tectonics and Water
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Intraplate Earthquakes and Water
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The Lithosphere is in a State of Failure
EquilibriumResulting in a Critically-Stressed
Crust
Zoback and others (2003)
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Critically-Stressed Crust KTB Stress Profile
Zoback and Harjes (1997)
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Permeability of Faulted Crust is High Which
Maintains Hydrostatic Fluid Pressure
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Strong Crust in Intraplate Areas Hydrostatic Pore
Pressure
Townend and Zoback (2001)
How Faulting Keeps the Crust Strong
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Dixie Valley, Nevada
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Steam Production From Stillwater Fault
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Earthquakes and Water Why are Plate Boundaries
Weaker Than Plates?
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S an A ndreas F ault O bservatory at D epth
Testing Fundamental Theories Of Faulting
Through Scientific Drilling
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USArray
A New View into Earth
SAFOD
A program for study of the structure, dynamics
and evolution of the North American continent
PBO
InSAR
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San Andreas Fault Observatory at DepthProject
Overview and Science Goals

• Test fundamental theories of earthquake
  mechanics
• Determine structure and composition of the fault
  zone.
• Measure stress, permeability and pore pressure
  conditions in situ.
• Determine frictional behavior, physical
  properties and chemical processes controlling
  faulting through laboratory analyses of fault
  rocks and fluids.
• Establish a long-term observatory in the fault
  zone
• Characterize 3-D volume of crust containing the
  fault.
• Monitor strain, pore pressure and temperature
  during the cycle of repeating microearthquakes.
• Observe earthquake nucleation and rupture
  processes in the near field.

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SAFOD Project History

• 1992 Asilomar Workshop on San Andreas Fault Zone
  Drilling
• 1994 Marconi Workshop on Site Characterization
• 1994 Menlo Park Workshop on Site Selection
• 1994 Geophysical Surveys of Middle Mountain
  Begin
• 1996 NSF Project Proposal
• 1998 NSF Proposal Package (with 68 PIs from U.S.
  Universities, USGS, DOE Labs and Foreign
  Institutions)
• 1999 EarthScope initiative first proposed by NSF
• 2000 Dense Seismic Network (PASO) Installed
• 2001 International Workshop on Borehole
  Instrumentation and Near-Source Seismology
• 2001 Parkfield Seismic Imaging Workshop
• 2002 Pilot Hole drilled, funded by ICDP (science
  funded by NSF and USGS) Site Characterization
  Studies employing downhole array begin
• 2003 EarthScope funded
• 2004 SAFOD Drilling Starts!

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• KEY QUESTIONS TO BE ADDRESSED WITH SAFOD
• Why are major plate-boundary faults like the San
  Andreas weak?
• What is the fluid pressure within and adjacent to
  the fault zone and how does it vary during a
  seismic cycle?
• What is the origin and composition of fault zone
  fluids?
• How do stress orientations and magnitudes vary
  across the fault zone?
• What factors control the nucleation, propagation,
  arrest and recurrence of earthquake rupture
• How are stress and strain transferred along or
  between faults over different time scales?
• What are the width and structure (geologic and
  thermal) of the active fault zone at depth?
• What are the mineralogies, deformation mechanisms
  and frictional properties of the fault rocks?
• What processes lead to the localization of
  deformation within the fault zone?
• What are the permeabilities of fault-zone
  materials and country rock?
• What is the extent of chemical water-rock
  interaction and how does this effect fault-zone
  behavior?
• What is the origin of low-velocity/high-electrical
  -conductivity zones associated with the fault
  zone?
• How is energy partitioned within the fault zone
  between seismic radiation, frictional heating and
  other processes?

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• KEY QUESTIONS TO BE ADDRESSED WITH SAFOD
• Why are major plate-boundary faults like the San
  Andreas weak?
• What is the fluid pressure within and adjacent to
  the fault zone and how does it vary during a
  seismic cycle?
• What is the origin and composition of fault zone
  fluids?
• How do stress orientations and magnitudes vary
  across the fault zone?
• What factors control the nucleation, propagation,
  arrest and recurrence of earthquake rupture?
• How are stress and strain transferred along or
  between faults over different time scales?
• What are the width and structure (geologic and
  thermal) of the active fault zone at depth?
• What are the mineralogies, deformation mechanisms
  and frictional properties of the fault rocks?
• What processes lead to the localization of
  deformation within the fault zone?
• What are the permeabilities of fault-zone
  materials and country rock?
• What is the extent of chemical water-rock
  interaction and how does this effect fault-zone
  behavior?
• What is the origin of low-velocity/high-electrical
  -conductivity zones associated with the fault
  zone?
• How is energy partitioned within the fault zone
  between seismic radiation, frictional heating and
  other processes?

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San Andreas Fault Observatory at Depth (SAFOD)
North American Plate
The central scientific objective of SAFOD is to
directly measure the physical and chemical
processes that control deformation and earthquake
generation within an active plate-bounding fault
zone.
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SAFOD Phase 1 Drilling Summer 2004 (Pilot Hole
drilled summer of 2002)
Phase 1 Rotary Drilling to 2.5 km Drill 12-1/4
hole to 2.5 km. Below kick-off point (1.5 km),
steer hole toward target earthquakes (deviation
55). After setting casing, obtain 20 m cores
at 1.5 and 2.5 km. Conduct permeability tests,
fluid sampling and hydrofracs in core
holes. Collect comprehensive suite of wireline
logs from 0.6 - 2.5 km (electrical and ultrasonic
imaging, density, porosity, resistivity, dipole
sonic, geochemical, temperature, etc.)
San Andreas Fault Zone
M 2.1 Target Earthquake
Resistivities Unsworth Bedrosian
2004 Earthquake locations Steve Roecker Cliff
Thurber 2004
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SAFOD Phase 2 Drilling Summer 2005
Phase 2 Drilling Through Fault Zone Drill
8-1/2 hole at 55 to 3.2 km Conduct full
Logging While Drilling suite (azimuthal density
and resistivity, porosity, fluid pressure,
acoustic, gamma). Periodic (up to 4) 10-m spot
cores. Side-wall cores if possible. Following
open-hole wireline logging (perhaps with
drill-pipe deployment), case and cement
hole. Conduct permeability tests, fluid sampling
and hydrofracs through perforations in cemented
casing (10 tests).
San Andreas Fault Zone
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SAFOD Phase 3 Drilling Summer 2007
San Andreas Fault Zone
Phase 3 Coring the Multi-Laterals Drill 4
multilateral core holes extending 250 m from main
hole. Depths to be determined from data obtained
in Phase 2, plus repeat logging for casing shear
and downhole seismic monitoring (2005-2007).
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SAFOD Observatory Monitoring Instrumentation Depl
oyment in 3 Distinct Stages
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San Andreas Fault Observatory at Depth (SAFOD)
North American Plate
Why this site?
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Slip rate inferred from geodetic measurements
1966-1991 (Murray et al. 2001)
Microseismicity 1984 - 1999, up to M 5 (Feliz
Waldhauser Bill Ellsworth)
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Relative Locations of SAFOD Target Earthquakes
(Repeaters)
SAFOD
Main SAF
Strand
Felix Waldhauser (2004)
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Publication of First Scientific Results

• GRL SPECIAL ISSUE PREPARING FOR THE SAN ANDREAS
  FAULT OBSERVATORY AT DEPTH
• PART 1 EARTHQUAKES AND CRUSTAL STRUCTURE, Vol.
  31, No 12, 2004 (10 papers)
• PART 2 THERMOMECHANICAL SETTING, PHYSICAL
  PROPERTIES AND MINERALOGY, Vol. 31, No. 15, 2004
  (10 papers)

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SAFOD Phase 1 - Status Drilling Finished
Ahead of Schedule Budget On budget On-Site
Activities 100 Successful Downhole
Measurements 100 Successful Coring and
Cuttings 100 Successful Minifrac -
Successful Fluid Sampling Not Successful. A
long term test is currently underway Observatory
Proceeding Well
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Real-Time Mud Gas Collecting and Analysis System

drill bit
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Pilot Hole Real-Time Mud Gas Logging Results
C isotopic analysis implies biogenic origin
3He/4He implies 9 mantle fluids
Gas composition suggests hydraulic communication
with shallow sed. section
lt 1 mantle fluids
Black lines oxide zones (Rymer). Grey bars
shear zones (Boness and Zoback, 2004)
Erzinger et al., 2004
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Why is There no Frictional Heat Detectable Along
the San Andreas Fault? Does the Fault Have Low
Frictional Strength?
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MECHANICAL IMPLICATIONS Heat-flow
constraint and fault-normal compression (SHmax
at 75or more to SAF) require either
1) Low friction (m 0.1) along the fault and
high friction elsewhere or
2) Super-lithostatic pore pressure confined to
the fault zone and/or 3)
Dynamic weakening mechanisms
37
The San Andreas Stress/Heat Flow Paradox
Mojave Desert Profile
Heat Flow Anomaly For 50 MPa Friction
Cajon Pass
Regional H.F. Average
Shallow H.F. Measurements
Brune et al. 1969 Lachenbruch Sass 1973, 1980,
1992

• Absence of heat-flow anomaly indicates San
  Andreas Fault much weaker than predicted by
  laboratory friction measurements (Byerlees Law).
• Groundwater flow not likely to erase thermal
  signature of strong SAF, even for wide range of
  assumed permeabilities (Saffer et al., 2003
  Fulton et al., 2004).

38
Williams et al 2004

• Absence of heat-flow anomaly indicates San
  Andreas Fault much weaker than predicted by
  laboratory friction measurements (Byerlees Law).
• Groundwater flow not likely to erase thermal
  signature of strong SAF, even for wide range of
  assumed permeabilities (Saffer et al., 2003
  Fulton et al., 2004).

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Fault-Normal Compression Adjacent to the San
Andreas and Calaveras Faults Indicates Extremely
Low Shear Stress
Calaveras Fault
Townend and Zoback (2001)
Peninsula Seismicity
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How does fluid pressure vary during the
earthquake cycle?
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What are the permeabilities of fault and country
rocks? What is the origin and composition of
fault zone fluids?
Middle Mt.
Kennedy et al. 1997
There is some support for this leaky fault zone
model from geochemical observations along the San
Andreas Fault.
Permeable conduit model requires continual fluid
input from deep crustal fault zone root.
43
What is the extent of chemical water-rock
interaction and how does this effect fault-zone
rheology?
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Fault Sealing and Permeability Reduction Field
and Laboratory Evidence
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Questions to be Addressed with SAFOD
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SAFOD
SAFOD Phase 2 Fluid sampling, pore pressure, and
least principal stress (mini fracs) through
perforations
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Need a title
Shear Heating Results in Dynamic Weakening
Simple prediction
Segall and Rice, in prep.
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MECHANICAL IMPLICATIONS Heat-flow
constraint and fault-normal compression (SHmax
at 75or more to SAF) require either
1) Low friction (m 0.1) along the fault and
high friction elsewhere or
2) Super-lithostatic pore pressure confined to
the fault zone and/or 3)
Dynamic weakening mechanisms
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h 3 mm Wibberley (priv. commun., 2003)
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Sept. 28, 2005
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Sept. 28, 2005
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Sept. 28, 2005
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• SAFOD Phase 1 - Status
• Mainshock and Aftershocks Caused no
  Operational, Technical or Scientific Problems
• Mainshock and Aftershocks Recorded on Pilot
  Hole Array
• Phase 2 Scheduled to get Underway in May 2005
  with a Fluid Sampling Test