The San Andreas Fault Observatory at Depth (SAFOD)
An integrated study of a major plate-bounding fault at seismogenic depths
Amy Day-LewisMark Zoback
Department of Geophysics, Stanford University
Stephen HickmanU.S. Geological Survey
SAFOD A borehole observatory across the San Andreas Fault to directly measure the physical conditions under which earthquakes occur
Plate Boundary Observatory A fixed array of GPS receivers and borehole strainmeters to measure real-time deformation on a plate-boundary scale
USArray A continental-scale seismic array to provide a coherent 3-D image of the lithosphere and deeper Earth
EarthScope – “A New View into the Earth”
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
The site is small,…
SAFOD
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
To directly measure the physical and
chemical processes that control
deformation and earthquake
generation within an active, plate-
bounding fault zone.
…but the goal is big.
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
our target
Microseismicity 1984 - 1999, up to M 5, F. Waldhauser & B. Ellsworth).
Slip rate inferred from geodetic measurements 1966-1991 (Murray et al. 2001).
1966 2004
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
GROUP 1 (10/20/03)
GROUP 2 (10/21/03)
GROUP 3 (6/27/01?)
primarySAFODtarget
in plane of SAF perpendicular to SAF
mainSAF
repeating micro-earthquakes
[Waldhauser, 2004]U.C. Berkeley (HRSN) stations JCN, MMN and VCA
S.F. L.A.
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
1) 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.
2) 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 – are earthquakes predictable?
specific objectives
1) 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.
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
multi-phase approach
Comprehensive Site Characterization
C. Thurber, S. Roecker
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Comprehensive Site Characterization
Pilot Hole• drilled in 2002 to 2.2
km MD/TVD• laid the scientific and
technical groundwork for SAFOD
• constrained local geology
• improved locations of target earthquakes M 2.1
Target Earthquake
San
An
dre
as F
ault
Zo
ne
San
An
dre
as F
ault
Zo
ne
Resistivities: Unsworth & Bedrosian 2004
Earthquake locations: Roecker & Thurber 2004
multi-phase approach
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Comprehensive Site Characterization
Pilot Hole Phase I Main Hole
• drilled in 2004 vertically to 1.5 km TVD, deviated 55° to 2.5 km TVD
• intense physical sample collection
• geophysical logging• hydrofracture tests• coring
M 2.1 Target Earthquake
San
An
dre
as F
ault
Zo
ne
San
An
dre
as F
ault
Zo
ne
multi-phase approach
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Comprehensive Site Characterization
Pilot Hole Phase I Main Hole Phase II Main Hole
• drilled in 2005 through the San Andreas Fault Zone to a final depth of 3.1 km TVD
• On-site mineralogical analysis
• MWD, LWD, and pipe-conveyed logging
• spot and sidewall coring
San
An
dre
as F
ault
Zo
ne
San
An
dre
as F
ault
Zo
ne
multi-phase approach
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Comprehensive Site Characterization
Pilot Hole Phase I Main Hole Phase II Main Hole Phase III Main Hole
• dedicated coring phase in 2007
• 4 multi-lateral cores drilled 250 m from the main hole
• on site core processing
San
An
dre
as F
ault
Zo
ne
San
An
dre
as F
ault
Zo
ne
multi-phase approach
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Comprehensive Site Characterization
Pilot Hole Phase I Main Hole Phase II Main Hole Phase III Main Hole Multi-stage
Observatory• 2007-2027• monitor strain, tilt,
pore pressure, temperature
• observe earthquakes in the near-field
San
An
dre
as F
ault
Zo
ne
San
An
dre
as F
ault
Zo
ne
Retrievable geophone, accelerometer, tilt meter, fluid pressure and temperature monitoring array inside casing
Fiber optic strain meter cemented behind casing
Retrievable geophone, accelerometer and tilt meter inside casing
multi-phase approach
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
benefits of this approach
Paulsson Geophysical ArrayPASO Array
earthquake locations by Zhang and Thurber
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
In the Field
continuous cuttings analysis
The mudloggers were the first to recognize SAFOD’s entry into sedimentary rock!
graniteseds
Fra
nci
scan
X
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
real-time mud gas logging
• Recognition of shear zones during drilling
• C isotope, 3He/4He → fluid origin (e.g., biogenic, mantle-derived)
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
geophysical logging
• hole orientation
• hole diameter (caliper)
• temperature
• gamma
• density
• seismic velocities
• electrical resistivity
• electrical and acoustic wellbore images
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
(Boness andZoback, 2004)
shear zones
stress relief
zones
log analysis
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
stress and wellbore stability analysis
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
coring
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
hornblende-biotite granodiorite
Phase I core: 1.5 km
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Phase I core: 2.5 km (top)pebble conglomerate and arkosic sandstones• consists almost entirely
of granitic debris, very little weathering
• grains poorly sorted and very poorly rounded
• grains tightly packed, with abundant grain-to-grain cracking
• pressure-solution features common
• matrix filled with crushed and recrystallized phylllosilicates, plus zeolites and carbonates
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Phase I core: 2.5 km (bottom)Core catcher contents from final run (Run #5, deepest rock cored): Heavily fractured and recemented granite or granite cobble conglomerate
Shear Zone
fine to very fine siltstone
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
• structural, petrologic and geochemical study of deformation and diagenesis
• mineral transformations and fabrics
• thermochronolgy (zircons)• brittle fracture, deformability,
permeability and seismic anisotropy
• thermal conductivity and radiogenic heat production
• fluid inclusion volatiles analysis
core “Sample Party,” February 2005
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Phase II core
Inoceramus fossils &
bioturbation
very fine sandstone, siltstone, and shale
photography (flat and 360° scans) &
continuous physical property scans
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
• one-foot-thick clay-rich zone, with abundant internal shearing (polished surfaces and slickensides)
• separates siltstone from heavily fractured and recemented granite cobble conglomerate.
shear zone at 3,067 m MD
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
on-site mineralogypetrographic examination of grain-mount thin sections
XRD and XRF analysis for mineralogy
magnetic susceptibility and remanant magnetization
heavy mineral separations for high-pressure Franciscan metamorphic minerals
All helped identify shear zones & lithologic changes (and the east side of the fault!).
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
real-time decision-makingft MD
firstmudstone
firstserpentine
changein beddingin image logs
major drillingbreak, gas kick
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
side-wall coring
52 1” cores recovered over open-hole interval (3,066–3,953 m MD)
depths selected to best sample lithologic, structural and physical property variations identified in real-time cuttings analysis (optical and XRD) and geophysical well logs, while avoiding highly washed-out zones
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
shales and mudstones
Core 23: 3,722 m
Core 38: 3,387 m Core 67: 3,126 m
Core 58: 3,213 m
fine- to coarse-grained sandstones
conglomerates (granite cobble?)
sidewall core examples
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
2005 to 2007
• repeat logging for casing shear
• collection of new regional and borehole seismic data to refine the location of the target events
• data integration to determine the optimum locations for Phase III coring
Hypocentroid locations determined by Felix Waldhauser using cross correlation measurements of NCSN waveforms and hypoDD.
Red: “S.F.” targetBlue: “L.A.” targetGreen: “S.W.” targetYellow: July 16, 2005 S.F. and
August 2, 2005 S.W.
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
3-Comp. Seismometer
Laser Strainmeter
Borehole Tiltmeter
early monitoring success
M 2.8 at 4 km distance
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
Geophysical Research Letters Volume 31 2004
Special Sections on the San Andreas Fault Observatory at Depth
• Part 1: Earthquakes and Crustal Structure (no. 12, 10 papers)
• Part 2: Thermomechanical Setting, Physical Properties and Mineralogy (no. 15, 10 papers)
Pilot Hole Results
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
AGU Fall Meeting, Session T11
San Francisco, CaliforniaDecember 5–9, 2005
Sponsored by the Tectonophysics and Seismology Sections
Conveners: Naomi Boness, Stanford andJohn Solum, USGS
Phase I and II Results
• physical properties• state of stress• geochemical analysis of
gases and fluids• borehole seismic studies• mechanical, petrological,
structural and microbiological analyses of cuttings and core
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005
SAFOD is funded by:
National Science Foundation
and the EarthScope Project
With co-principal investigators:
William Ellsworth and Stephen Hickman, U.S. Geological Survey, and
Mark Zoback, Stanford University
And assistance by:
International Continental Scientific Drilling Program
A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005