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Amy Day-Lewis Mark Zoback Department of Geophysics, Stanford University Stephen Hickman

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. EarthScope – “A New View into the Earth”.

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Amy Day-Lewis Mark Zoback Department of Geophysics, Stanford University Stephen Hickman

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  1. 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

  2. EarthScope – “A New View into the Earth” 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 A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  3. The site is small,… SAFOD A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  4. …but the goal is big. To directly measure the physical and chemical processes that control deformation and earthquake generation within an active, plate-bounding fault zone. A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  5. 1966 2004 our target Slip rate inferred from geodetic measurements 1966-1991 (Murray et al. 2001). Microseismicity1984 - 1999, up to M 5, F. Waldhauser & B. Ellsworth). A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  6. U.C. Berkeley (HRSN) stations JCN, MMN and VCA repeating micro-earthquakes in plane of SAF perpendicular to SAF GROUP 1 (10/20/03) primary SAFOD target main SAF S.F. L.A. GROUP 2 (10/21/03) GROUP 3 (6/27/01?) [Waldhauser, 2004] A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  7. 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. 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? A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  8. Comprehensive Site Characterization multi-phase approach C. Thurber, S. Roecker A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  9. 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 multi-phase approach San Andreas Fault Zone M 2.1 Target Earthquake Resistivities: Unsworth & Bedrosian 2004 Earthquake locations: Roecker & Thurber 2004 A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  10. 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 multi-phase approach San Andreas Fault Zone M 2.1 Target Earthquake A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  11. 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 multi-phase approach San Andreas Fault Zone A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  12. 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 multi-phase approach San Andreas Fault Zone A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  13. 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 Andreas Fault Zone multi-phase approach Fiber optic strain meter cemented behind casing Retrievable geophone, accelerometer, tilt meter, fluid pressure and temperature monitoring array inside casing Retrievable geophone, accelerometer and tilt meter inside casing A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  14. earthquake locations by Zhang and Thurber Paulsson Geophysical Array PASO Array benefits of this approach A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  15. In the Field

  16. seds granite Franciscan X The mudloggers were the first to recognize SAFOD’s entry into sedimentary rock! continuous cuttings analysis A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  17. 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

  18. 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

  19. log analysis stress relief zones shear zones (Boness and Zoback, 2004) A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  20. stress and wellbore stability analysis A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  21. coring A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  22. Phase I core: 1.5 km hornblende-biotite granodiorite A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  23. 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 Phase I core: 2.5 km (top) A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  24. 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

  25. core “Sample Party,” February 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 A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  26. Phase II core very fine sandstone, siltstone, and shale Inoceramus fossils & bioturbation • photography (flat and 360° scans) & • continuous physical property scans A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  27. shear zone at 3,067 m MD • one-foot-thick clay-rich zone, with abundant internal shearing (polished surfaces and slickensides) • separates siltstone from heavily fractured and recemented granite cobble conglomerate. A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  28. 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 3-4 2005

  29. ft MD firstmudstone firstserpentine changein bedding in image logs major drillingbreak, gas kick real-time decision-making A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  30. 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 side-wall coring A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  31. sidewall core examples conglomerates (granite cobble?) fine- to coarse-grained sandstones Core 38: 3,387 m Core 67: 3,126 m shales and mudstones Core 23: 3,722 m Core 58: 3,213 m A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  32. 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 2005 to 2007 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 3-4 2005

  33. early monitoring success Laser Strainmeter 3-Comp. Seismometer Borehole Tiltmeter M 2.8 at 4 km distance A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  34. Pilot Hole Results • 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) A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  35. physical properties state of stress geochemical analysis of gases and fluids borehole seismic studies mechanical, petrological, structural and microbiological analyses of cuttings and core Phase I and II Results 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 A. Day-Lewis, CLSI Workshop, Tokyo, October 3-4 2005

  36. 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

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