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Rock Properties and Internal Structure of the San Andreas Near ~ 3 km Depth in the SAFOD Borehole Based on Meso- to Micro-scale Analyses of Phase III Whole Rock Core

Kelly Keighley Bradbury Utah State University

James P. Evans Utah State University

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Recommended Citation Bradbury, Kelly Keighley and Evans, James P., "Rock Properties and Internal Structure of the Near ~ 3 km Depth in the SAFOD Borehole Based on Meso- to Micro-scale Analyses of Phase III Whole Rock Core" (2010). Geosciences Presentations. Paper 5. https://digitalcommons.usu.edu/geology_pres/5

This Poster is brought to you for free and open access by the Geosciences at DigitalCommons@USU. It has been accepted for inclusion in Geosciences Presentations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. TA41A-2099 Rock properties and Internal Structure of the San Andreas Fault at ~ 3km depth in the SAFOD Borehole: Mesoscopic to Microscopic Analyses of Phase III Whole Rock Core By Kelly Keighley Bradbury ([email protected]) and James P. Evans ([email protected]), Department of Geology, Utah State University, 4505 Old Main Hill, Logan, UT I. Introduction III. Mesoscopic to Microscopic Core-Based Studies V. Whole-Rock Geochemistry We examine the relationships between rock properties and structure within ~ 41 m Lithology & Mineralogical Composition Deformation-Related Features of PHASE III whole-rock core collected from ~ 3 km depth along the SAF in the San Hole E Core Images b c Lithologies encountered include (reported in measured core depths): d 3150 m 3192.5 m 3195.8 m Major Elements a Andreas Fault Observatory at Depth (SAFOD) borehole, near Parkfield, CA. Arkosic sandstones [3141 - 3144.5 m and 3145.8 - 3152.6 m] XRF results from SAFOD Sheared black silty shale [3144.5 - 3145.7 m]

Direct mesoscale observations of the core are integrated with detailed petrography 1906 M 7.8 Black ultrafine-grained rocks [3192.9 – 3196.4 m] cuttings data for the main San Francisco Phyllosilicate-rich (± serpentinite-bearing) block-in-matrix or mélange and microstructural analyses coupled with X-Ray Diffraction and X-ray Fluorescence 1989 M 6.9 fault rocks [3186.7 - 3196.4 m; 3198.4 - 3311.8 m] borehole (D. Kirschner, NA Plate 3151 m techniques to document variations in composition, alteration, and structures that Alternating beds and/or blocks of siltstone, sandstone, and shale 3142 m 3144.6 m 3151 m SAFOD 2004;1966 M ~ 6.0 d 3196.7 m 3197.8 m pers. comm). Samples from may be related to deformation and/or fluid-rock interactions. 1857 M 7.9 [3294.9 – 3311.8 m ]. Hole G Core Images f 3297.8 m g h e g core area are highlighted in Across the low velocity zone (LVZ) defined by borehole geophysical data, lithologies Los Angeles % of Total Sampled Core Lithostratigraphic Units the outlined box and shown ~ 48 mm/yr 3% Lithic arkose are comprised of a heterogeneous sequence of fine-grained sandstones, siltstones, 1% 3305.7 m 3312.1 m 3.3% Feldspathic Arkose below. mudstones, and shale with block-in-matrix textures and pervasively foliated fabrics. 4% Silty black shale/mudstone 3192.7 m 3193.7 m 3193.7 m 7.6% Phyllosilicate-rich melange More competent clasts within the block-in-matrix materials exhibit pinch-and-swell Study Area Location 0.7% 3192.9 m Black cataclasite to ultracataclasite shaped structures with crosscutting veins that do not extend into the surrounding Siltstone with carbonate veining j Banded siltstone i LOI Sheared black silty shale phyllosilicate-rich matrix. 14% 16.6% Massive graywacke k zone with veining (Sh1) Discrete microfaults with slickenlines to cm-wide zones of cataclasite Narrow fault strands at 3192 and 3302 m bound the LVZ and correspond to sites of active casing deformation (aseismic 6% Fault rocks (FZ1 and FZ2) Serpentinite (S) 3198.7 m and/or clay gouge, pinch-and swell clasts with extensional veins, lens- creep). Here, the rock consist of ~ 2 m thick serpentinite-bearing phyllosilicate gouge with a pervasive penetrative scaly clay 3300 m 3311 m 42.5% shaped (phacoidal) clasts with apparant structural order (Sills et al., fabric and phacoidal-shaped clasts. Bounding these two active slip surfaces are highly sheared and comminuted ultrafine- 2009), scaly , localized veining, black staining (see Janssen et grained black fault rocks with abundant calcite veins parallel and oblique to orientation. al., 2010), mineralization (calcite, pyrite), neomineralized clay ***In ~ 41 m total core have over 65% weak minerals/lithologies coatings (see Schleicher et al., 2010) clast or block

Localized shear surfaces bound multi-layered zones of medium to ultra-fine grained cataclasite in the near-fault environ- Ultracataclasite ~ Black Rock 3193.9 ment and record multiple generations of brittle deformation processes. Fault Rocks and Alteration 3193.6 m X-Ray Diffraction of 3193.9 m associated with SDZ casing deformation black cataclasite fault identified by Zoback et al. (2010) cataclasite slip localization rock at 3193.6 m Deformation at high-strain rates is suggested by the presence of crack-seal veins in clasts within the block-in-matrix materi- chrysotile gouge? measured core depth. Fault Gouge associated with CDZ casing deformation identified by Zoback et al. (2010) als, the presence of porphyroclasts, and the development of S-C fabrics in the phyllosilicate-rich gouge. Across the fault(s) Note accessory minerals. block or clast Calcite-rich within clast and related damage zones, foliated fabrics alternating with discrete fractures suggest a mixed-mode style of deformation XRF including both ductile and brittle deformation processes during the temporal and spatial evolution of the fault zone. 3192.7 m 3196.1 m 1 mm 1 mm 100 μm Quartz Si O2 block or clast garnet? basalt lithic Magnetite block or clast Evidence for fluid-rock interaction across the fault zone is indicated by depletion of Si and enrichment of MgO, FeO, and Fe +2 Fe2 +3 O4 LOI values range Quartz Si O2 Albite Si Al CaO; with significant clay alteration and/or growth of neo-mineralized vein fillings and fracture surface coatings. Shear local- X-Ray Diffraction of ( Na , Ca ) Al ( Si , Al )3 O8 Magnetite Sepiolite from 5-24% suggesting Fe +2 Fe2 +3 O4 black cataclasite fault Mg4 Si6 O15 ( O H )2 ·6 H2 O Chlorite-serpentine ization may decrease porosity and inhibit fluid flow whereas fracturing may locally facilitate fluid migration and/or chemical Kaolinite Carbon Values rock at 3193.9 m ( Mg , Al )6 ( Si , Al )4 O10 ( O H )8 Al2 Si2 O5 ( O H )4 significant hydration Kamacite? alteration within the fault zone. Results reveal the complex internal structure and fluid-rock interactions within the San An- Andradite measured core depth. ( Fe , Ni ) 3197.7 m 3297.9 m Ca3 Fe2 ( Si1.58 Ti1.42 O12 ) dreas Fault at shallow crustal levels and provide a geologic context, which can be used for further core-based studies and 1 mm 1 mm Palygorskite Mg Al Si4 O10 ( O H ) ·4 H2 O experimental analyses. reworked altered serpentinite clast cataclasite Summary Results: Trace Elements The penetrative scaly fabric within the phyllosilicate-rich block-in-

matrix sequences is ubiquitous throughout the low velocity zone and SiK 100um AlK 100um 3297.8 m surrounds the main active slip surfaces and associated serpentinite- 200x kV:10.0 Tilt:0 200x kV:10.0 Tilt:0 X-Ray Diffraction of bearing clay fault gouges. 3297.7 m serpentinite-bearing S Ca II. Geologic and Geophysical Setting 1 mm 3297.8 m The penetrative and highly sheared nature of the fabric at the meso- fault gouge at scale, consisting of anastomosing slip surfaces weaving around foliated gouge altered clasts garnet porphyroclast 3297.8 m measure phacoidal shaped lozenges with striated and/or polished slip surfaces Surface Geology Borehole Geometry core depth. Note extends down to the microscale. Borehole Velocity Logs accessory minerals. Tu Some of these thin, anastomosing surfaces, may accommodate active KJf 36°02’30” & ! Tm 3000 m MD slip along the fault, while others may record continuous deformation 3 Tm Serp. Vs processes related to aseismic creep (Faulkner et al., 2003). Lithology Based on Cuttings 2.5 3298.4 m Saponite KJf 2 1 mm 500 μm Ca0.2 Mg3 ( Si , Al )4 O10 ( O H )2 ·4 H2 O QTp Development of this fabric in the phyllosilicate-rich rocks may also Buzzard Canyon Fault SAFSan Andreas Fault S K 100um CaK 100um Tm Southwest zone of Casing Clinochrysotile 200x kV:10.0 Tilt:0 200x kV:10.0 Tilt:0 SAFOD BCF Mg3 ( Si2-x O5 ) ( O H )4-4x enhance fluid-rock interactions and the rate of neomineralized growth Tu Qls 5 Kgv? 0 85° Q/T Vp Photomicrographs of samples from within the Te Tm 4 Deformation (SDZ) Ankerite by creating pathways for fluid flow (Schleichler et al., 2010) and might SEM and EDAX Images from the black cataclasite rock bounding sediments Ca ( Mg0.67 Fe0.33 +2 ) ( C O3 )2 Qal Tu 3 ~ 3192 m SDZ and CDZ regions of casing deformation highlight also help to focus or channelize fluids. The mixed fault gouge and Quartz the southwestern margin of the SDZ at 3193.9 m measured core Qal 500 Central zone of Casing related damage zone regions comprised of block-in-matrix materials San Andreas the nature of foliated fault gouge, melange texture, Si O2 Fault Zone TMT Qls Salinian Nontronite of varying strength may reflect heterogeneous continuous- depth granite Deformation (CDZ) areas of slip localization, and distinct mineral ( Na , Ca )0.3 Fe2 ( Si , Al )4 O10 ( O H )2 ·x H2 O KJf/Qls ~ 3302 m discontinuous deformation as described by Fagargeng and Sibson 36° 1000 QTp assemblages. (2010), whereas the ultrafine black rocks may reflect older slip events. KJf PA Plate LVZ ! Values of Ni and Cr are BCFZ ? Tertiary arenite Te 1500 Kp ± arkose Tu ± siltstone 3500 m MD very high within the Qal Tm Tu Tvr Te 2000 IV. Physical Rock Properties SAFOD Qls N Qal [m] depth Vertical serpentinite-bearing Carbon values approach petroliferous Qf Pilot Melange or block-in-matrix textures GHF 2500 Hole Borehole Logging Data (Jeppson et al., 2010) quantity within several fault rocks QTp fault gouge samples K/T sandtones, Vp Vs Poisson's Ratio Gamma Ray Porosity Density Tu 1966 Qf Boxed area 3000 9836.7 Hole G Run 1 Section 2 Rupture Modified 1 km Qal highlights siltstones, dmod=maximum observed dimension Kg Phase III core NA Plate mudstones, From Jeppson dmod range=.5-13.5 Qal 35°57’30” 3000 0 cm Tu shales 3100 #clasts=59 (74) BCFZ = Buzzard Canyon Fault Zone Kg Low Velocity (Vp & Vs) Zone et al., (2010); TMT = Table Mountain Thrust Qal QTp ? 87 cm Tsm at SAFOD Data from 0 5 10 cm 1.9 2.5 GHF = Gold Hill Fault 4.5 2.9 1.7 Qal 2.6 1.1 3200 10492.5 3.1 3500 as defined by Zoback et al (2010) C. Thurber, 2.7 11.5 4 Excursions in velocity, resistivity, 10.1 1.7 1.1 1.1 VI. Conclusions 120° 33’30” 120° 30’ ~3192 (SDZ) 5 5.2 13.5 (pers. comm) 4.3 Modified from Bradbury et al (2007) and references 3.3 SW 0 500 1000 1500 2000NE & porosity are observed 4 3.9 3300 1.2 therein ~3302 (CDZ) within the SAFOD borehole 1.4 3.3 1.5 7.2 1.1 Composition of rocks and structural features in the core show that the near-fault environment of the SAF is a complex zone of predominately fine- to 2.6 2.3 3.1 3400 11148.3 .8 3.1 9.2 1.1 1 1.6 3 1.5 near major lithologic boundaries .9 2.2 Depth (ft) Depth 4.4 1.3 2.4 3 1.7 2.3 4.1 .5 2.3 7.8 2.6 2.1 ultrafine-grained lithologies, containing localized zones of slip within broader zones of distributed deformation. This is consistent with recent work 1.5 4 3.9 2.9 4.6 2.1 3500 or in association with fault rocks Internal Fault Zone Structure from Phase III Core Observations Depth (m) suggesting mixed modes of deformation behavior may occur during the spatial and temporal evolution of a major plate-bounding fault (e.g., Fager- 3600 11804 Hole G Run 6 Section 5 ang and Sibson, 2010; Marone and Richardson, 2010). dmod=maximum observed dimension Shear Modulus Poisson’s Ratio dmod range=.6-12.3 3700 (GPa) #clasts=9(9) ~3141 0 cm Characterization of SAFOD core provides important details concerning the rock properties of the SAF and addresses topics including: Summary Result: 0 5 10 cm 88 cm 3800 12459.8 Significant internal structural and compositional 9.5 12.3 3900 ~ 53 blocks/m & variability at the meter to submeter scale - the Surface Geology 1) Development of weak minerals (e.g. serpentine) within phyllosilicate-rich fault rocks or as coatings along fracture surfaces (Schleicher et al., 2010) 4000 which may exhibit deformation either through aseismic creep or may demonstrate significant velocity weakening and/or unstable frictional behavior 3 4 5 6 2 2.5 3 0.08 0.16 0.24 0.32 40 80 120 160 0 10 20 2.2 2.4 2..6 Average Dmod* = 2.9 km/sec km/sec API % g/cc 9.8 .6 scale at which earthquakes occur 1 1 .8 4.2 (e.g.Reinen et al., 1994; Reinen et al., 2000; Moore et al., 1997; Saffer et al., 2001; Jeffries et al., 2006; Moore and Rymer, 2007; Niemeijer and Spiers, Multiple slip surfaces and zones of mineralization- Summary Result: 4.3 2.54 cm ~ 20 blocks/m 2007; Collettini et al., 2009) A ? and alteration Moduli are highly variable but significant reduction Average Dmod* = 2.2 occurs over the broader region of the low velocity Hole G Runs 1 and 2 Hole G Runs 4, 5, and 6 zone and within the regions of casing deformation 2) Role of extensive network of foliation surfaces on fault slip and deformation behavior (Colletini et al., 2009) gap in core SDZ Near the SDZ and CDZ, fault rocks exhibit block-in- dmod values (cm) dmod values (cm) Fault Core Gouge 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 18 20 Moderate Deformation matrix or melange textures 3186.7 m 3304.8 m 3) Precipitation and dissolution reactions related to fluid-rock interactions which may affect the rate at which rock properties change and how they ≥ 11 m thick B ~ 2.5 m thick Greatest reduction in shear modulus associated are distributed within the fault zone (Goddard and Evans, 1995; Schulz and Evans, 1998; Wibberley et al., 2008; Colletini et al., 2009) C with black ultracataclasite or phyllosilicate-rich, CDZ serpentinite-bearing fault rock lithologies 4) An estimate of the proportions and distribution of competent vs. incompetent materials (Lindquist and Goodman, 1994; Medley, 1994; Fagereng Pervasive Deformation D Fault Core Gouge Between 3000 ~ 4000 m: and Sibson, 2010). ≥ 13 m thick E ? ~ 1.6 m thick Average Shear Modulus Average Poisson’s Ratio Mineralized F ~ 14 blocks/m Above SDZ ~ 21 GPa Above SDZ ~ 0.27 gap in core Average Dmod* = 3.9 3311.8 m SDZ region ~ 15 GPa SDZ region ~ 0.25 3194 m ~ 3.5 m thick *top core measurements only VI. References *top core measurements only CDZ region ~ 15.5 GPa CDZ region ~ 0.26 Bradbury et al (in revision), EPSL Mineralized G Bradbury, K.K., Barton, D.C., Solum, J.G., Draper, S.D., and Evans, J., 2007, Mineralogic and textural analyses of drill cuttings from the San Andreas Fault Observatory at Depth (SAFOD) boreholes: Initial interpretations of fault zone composition and constraints on geologic models: Geosphere, 3, 299-318, ~3313 doi: 10.1130/GES00076.1. ≥ 1 m thick Bradbury, K.K., Evans, J., Lowry, A.R., and Jeppson, T., 2009, Integration of geology and borehole geophysics to characterize rock properties at the San Andreas Fault Observatory at Depth (SAFOD) site, near Parkfield, CA, RMGSA Section 61st Meeting, Geol. Soc. Amer. Abs. Prog., 41, 6, 13. Gas rich zones Elastic Moduli 100 m Average A pervasive block-in-matrix (Medley and Goodman, 1994) or melange fabric exists throughout the core in Colletini, C., Niemeijer, A., Viti, C., and Marone, C., 2009, Fault zone fabric and fault weakness: Nature, 462, 907-910, doi: 10.1038/nature08585. !"#$$"%&$'()*"' Fagereng A., and Sibson, R.H., 2010, Melange rheology and seismic style: Geology, 38, 8, 751-754, doi: 10.1130/G30868.1. H Faulkner, D.R., Lewis, A.C., and Rutter, E.H., 2003, On the internal structure and mechanics of large strike-slip fault zones; field observations of the Carboneras Fault in southeastern Spain: Tectonophysics, 367, 235–251, doi: 10.1016/S0040-1951(03)00134-3. (after Weirsberg & Erzinger, !# &!# (!# '!# )!# !!# *!# Hole G. Pinch-and-swell shaped blocks of higher competency are enclosed by anastomosing shear sur- Goddard, J., and Evans, J., 1995, Chemical changes and fluid-rock interaction in faults of crystalline thrust sheets, northwestern Wyoming, U.S.A.: J. of Struct. Geol., 15, 4, 533-547, doi: 10.1016/0191-8141(94)00068-B. ")&!#Poisson’s")(!# ")'!#Ratio Summary Result: Modified from Bradbury et al (under revision) 2008) 500 m!""# Jeffries, S., Holdsworth, R.E., Shimamato, T., Takagi, H., Lloyd, G.E., and Spiers, C.J., 2006, Origin and mechanical significance of foliated cataclastic rocks in the cores of crustal-scale faults: examples from the Median Tectonic Line, Japan: J. Geophys. Res., 111, B12303, 1-17, doi: 10.1029/2005JB004205. !""# faces and matri materials comprised of phyllosilicate-rich, lower competency rocks. $""# Plotting moduli for the Lindquist E.S. and Goodman, R.E., 1994, The strength and deformation properties of a physical model of melange, in: Nelson, , and Laubach, S.E., (Eds.), Proc. 1st North American Conference (NARMS), Austin, TX, 843-850. Zones of Casing Deformation 500 $""#m Jeppson, T.N., Bradbury, K.K., and Evans, J.P, 2010, Geophysical properties of the San Andreas fault zone a the San Andreas fault Observatory at Depth (SAFOD) and their relationship to rock properties: J. Geophys. Res., doi:10.1029/2010JB007563. Pervasive Deformation (Zoback et al., 2010) 900 m%""# entire borehole at the 100 Marone, C., and Richardson, E., 2010, Learning to read fault-slip behavior from fault-zone structure, Geology, 38., 8, 767-768, doi: 10.1130/focus082010.1. %""# Pinch-and-swell shaped clasts vary in terms of degree of deformation and in diameter from < 1 mm to 19 cm Medley, E.W., and Goodman, R.E., 1994, Estimating the block volumetric proportions of mélanges abd similar block-in-matrix rocks (bimrocks) in Nelson, , and Laubauch, S.E., (Eds.), Rock Mechanics Models and Measurement Challenges from Industry, Proceedings, 1st North American Rock Mechanics &&""# ≥ 13 m thick &&""# m-average scale highlights (Figure 4), yet exhibit a preferred orientation trending ~ 40° to 90° to the core axis. In general, the average Symposium, Austin, TX, May 1994, 851-858. &'""# Moore, D.E., Lockner, D.A., Shengli, M., Summers, R., and Byerlee, J., 1997, Strengths of serpentinite gouges at elevated temperatures: J. Geophys. Res., 102, 14787-14801, doi:10.1029/97JB00995. &'""# major shifts within the longest clast diameter (dmod after Medley and Goodman, 1994) increases towards the base of Hole G with Moore, D.M., and Rymer, M.J., 2007, Talc-bearing serpentinite and the creeping section of the San Andreas fault: Nature, 448, 795-797, doi: 10.1038/nature06065. &!""# Neimeijer . A.R., and Spiers, C.J., 2007, A microphysical model for strong velocity weakening in phyllosilicate-bearing fault gouges: J. Geophys. Res., 112, B10405, doi: 10.1029/2007JB005008. &!""# Fracture intensity increases down core with Sheared fine-grained interval comprised Reinen, L.A., Weeks, J.D., and Tullis, T.E., 1994, The frictional behavior of serpentinite: implications for asesimic creep on shallow crustal faults: Geophys. Res. Lett., 18, 10, 1921-1924. Calcite veins, , pyrite mineralization &$""# shear moduli and Poisson’s the average number of total clasts per meter significantly decreasing with increasing core depth (see above system of discrete slickenlined slip surfaces, of black injection-like staining & ≤ cm- scale thick &$""# Reinen, L.A., 2000, Seismic and aseismic slip indicators in serpentinite gouge: Geology, 28, 135-138, doi: 10.1130/0091-7613(2000)28<135:SAASII>2.0.CO;2. &%""# ratio throughout the Figures). Near the two main slip surfaces at ~ 3192 and ~ 3302 m, block Saffer, D.M., Fryer, K.M, Marone, C., and Mair, K., 2001, Laboratory results indicating complex and potentially unstable frictional behavior of smectite clay: Geophys. Res. Lett., 28, 12, 2297-2300. A C F +,-./#0123435#Shear Modulus &%""# or multilayered zones of cataclasite; stylolites zones of cataclasite to ultra-cataclasite; extensive Lame’s Schleicher, A.M., B.A. van der Pluijm, and L.N. Warr, 2010, Nanocoatings of clay and creep of the San Andreas fault at Parkfield, California.?Geology, 38, 667-670, doi: 10.1130/G31091.1. (&""# 6.0-75#8195:.9:# frequency increases, whereas dmod block sizes decreases. Phyllosilicate-rich gouge with altered 2100 m Buzzard Canyon Fault Constant (&""# SAFOD borehole Schulz, S.E., and Evans, J., 2000, Mesoscopic structure of the Punchbowl fault, southern California, and the geological and geophysical structure of active faults: J. of , 22, 913–930, doi: 10.1016/S0191-8141(00)00019-5. veining at the ≤ mm scale. ;139<75#0123435#Young’s Zoback, M.D., Hickman, S.H., and Ellsworth, W.L., 2010, Scientific Drilling Into the San Andreas Fault Zone: Eos, Transactions, American Geophysical Union, 91, 22, 197-204. ('""# Block-in-matrix melange fabric: pinch-and- serpentinite as sub-rounded to rounded blocks Modulus ('""# *+,--+./-# 012+# G &/or clasts (!""# (!""# swell shaped clasts , some with abundant Unaltered Serpentinite The apparent maximum block dimension (dmod) were determined by core mapping and measurements B ($""# veins, are embedded witihin a phyllosilicate- ($""# for the melange-type units in Hole G (after Medley and Lindquist, 1995). D Block-in-matrix melange fabric: pinch-and-swell shaped Average 100 m values: VII. Acknowledgements rich matrix; vitreous fracture surfaces (%""# (%""# Phyllosilicate-rich gouge with altered Shear Modulus 5-31 GPa to phacoidal clasts some with abundant veins '&""# This work was supported by NSF-Earthscope grants EAR-044527 and 0643027 to Evans, and EAR-0346190. Bradbury received supplementary support for H 3100 '&""#m Block proportions and relative competency can influence deformation style and overall mechanical be- serpentinite as sub-rounded to rounded blocks embedded witihin a phyllosilicate-rich matrix; Low Velocity Zone Lames Constant 1-49 GPa E 3300 ''""#m ''""# havior of fault zones (Fagereng and Sibson, 2010; Medley and Goodman, 1994). sample analyses and travel to the IODP Gulf Coast Repository (GCR) from DOSECC, SEG Foundation, AAPG, SPWLA Foundation, and the GDL Foundation, &/or clasts deformation intensity appears to decrease with depth Youngs Modulus 12-78 GPa '!""# '!""# and through the Peter Mckillop Scholarhsip, USU Geology Dept. XRF analyses were performed by WSU laboratory. We thank Bradley Weymer and Phil whereas pyrite mineralization increases at least locally '$""# Poisson’s Ratio 0.1 - 0.37 3700 '$""#m 3700 m Rumford at the GCR Laboratory for cutting and processing the SAFOD core, their patience in helping us to obtain our core samples, and for their efforts at core scale towards caring and preserving this core. This work has benefited from numerous discussions with Anthony Lowry and John Shervais. We are grateful for help from USU undergraduate student,Dave Richie, for sample prepartion and some assistance with graphics.