The San Andreas Fault Observatory at Depth (SAFOD) An integrated study of a major plate-bounding fault at seismogenic depths Amy Day-Lewis Mark Zoback Department of Geophysics, Stanford University Stephen Hickman U.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

The site is small,… SAFOD A. Day-Lewis, CLSI Workshop, Tokyo, October

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

our target Microseismicity , up to M 5, F. Waldhauser & B. Ellsworth). Slip rate inferred from geodetic measurements (Murray et al. 2001) A. Day-Lewis, CLSI Workshop, Tokyo, October

GROUP 1 (10/20/03) GROUP 2 (10/21/03) GROUP 3 (6/27/01?) primary SAFOD target in plane of SAFperpendicular to SAF main SAF 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

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

multi-phase approach  Comprehensive Site Characterization C. Thurber, S. Roecker A. Day-Lewis, CLSI Workshop, Tokyo, October

 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 Andreas Fault Zone Resistivities: Unsworth & Bedrosian 2004 Earthquake locations: Roecker & Thurber 2004 multi-phase approach A. Day-Lewis, CLSI Workshop, Tokyo, October

 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 Andreas Fault Zone multi-phase approach A. Day-Lewis, CLSI Workshop, Tokyo, October

 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 Andreas Fault Zone multi-phase approach A. Day-Lewis, CLSI Workshop, Tokyo, October

 Comprehensive Site Characterization  Pilot Hole  Phase I Main Hole  Phase II Main Hole  Phase III Main Hole dedicated coring phase in multi-lateral cores drilled 250 m from the main hole on site core processing San Andreas Fault Zone multi-phase approach A. Day-Lewis, CLSI Workshop, Tokyo, October

 Comprehensive Site Characterization  Pilot Hole  Phase I Main Hole  Phase II Main Hole  Phase III Main Hole  Multi-stage Observatory monitor strain, tilt, pore pressure, temperature observe earthquakes in the near-field San Andreas Fault Zone 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

benefits of this approach Paulsson Geophysical Array PASO Array earthquake locations by Zhang and Thurber A. Day-Lewis, CLSI Workshop, Tokyo, October

In the Field

continuous cuttings analysis The mudloggers were the first to recognize SAFOD’s entry into sedimentary rock! granite seds Franciscan X A. Day-Lewis, CLSI Workshop, Tokyo, October

real-time mud gas logging Recognition of shear zones during drilling C isotope, 3 He/ 4 He → fluid origin (e.g., biogenic, mantle-derived) A. Day-Lewis, CLSI Workshop, Tokyo, October

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

(Boness and Zoback, 2004) shear zones stress relief zones log analysis A. Day-Lewis, CLSI Workshop, Tokyo, October

stress and wellbore stability analysis A. Day-Lewis, CLSI Workshop, Tokyo, October

coring A. Day-Lewis, CLSI Workshop, Tokyo, October

hornblende-biotite granodiorite Phase I core: 1.5 km A. Day-Lewis, CLSI Workshop, Tokyo, October

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

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

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

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

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

on-site mineralogy petrographic 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

real-time decision-making ft MD first mudstone first serpentine change in bedding in image logs major drilling break, gas kick A. Day-Lewis, CLSI Workshop, Tokyo, October

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

shales and mudstones Core 23: 3,722 m Core 38: 3,387 mCore 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

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.” target Blue:“L.A.” target Green:“S.W.” target Yellow:July 16, 2005 S.F. and August 2, 2005 S.W. A. Day-Lewis, CLSI Workshop, Tokyo, October

3-Comp. Seismometer Laser Strainmeter Borehole Tiltmeter early monitoring success M 2.8 at 4 km distance A. Day-Lewis, CLSI Workshop, Tokyo, October

Geophysical Research Letters Volume 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

AGU Fall Meeting, Session T11 San Francisco, California December 5–9, 2005 Sponsored by the Tectonophysics and Seismology Sections Conveners: Naomi Boness, Stanford and John 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

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