Lithology and internal structure of the San Andreas fault at depth based on characterization of Phase 3 whole-rock core in the San Andreas Fault Observatory at Depth (SAFOD) borehole

Bradbury, Kelly K.; Evans, James P.; Chester, J. S.; Chester, F. M.; Kirschner, David

doi:10.1016/j.epsl.2011.07.020

Cited by 63 publications

(69 citation statements)

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“…Experiments on cuttings from the CDZ document a low coefficient of friction (μ < 0.25), low (near-zero) rates of frictional healing, and strong localization of these mechanical properties to the creeping gouge zone [Carpenter et al, 2011]. These behaviors are correlated with the presence of magnesium-rich clays, suggesting that clay mineralogy is an important control on the strength and healing behavior of the fault, at least at these depths [e.g., Schleicher et al, 2010;Bradbury et al, 2011;Holdsworth et al, 2011;Hadizadeh et al, 2012;Richard et al, 2014].…”

Section: 1002/2015jb011963mentioning

confidence: 99%

Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

2015

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We present results from a comprehensive laboratory study of the frictional strength and constitutive properties for all three active strands of the San Andreas Fault penetrated in the San Andreas Observatory at Depth (SAFOD). The SAFOD borehole penetrated the Southwest Deforming Zone (SDZ), the Central Deforming Zone (CDZ), both of which are actively creeping, and the Northeast Boundary Fault (NBF). Our results include measurements of the frictional properties of cuttings and core samples recovered at depths of ~2.7 km. We find that materials from the two actively creeping faults exhibit low frictional strengths (μ = ~0.1), velocity‐strengthening friction behavior, and near‐zero or negative rates of frictional healing. Our experimental data set shows that the center of the CDZ is the weakest section of the San Andreas Fault, with μ = ~0.10. Fault weakness is highly localized and likely caused by abundant magnesium‐rich clays. In contrast, serpentine from within the SDZ, and wall rock of both the SDZ and CDZ, exhibits velocity‐weakening friction behavior and positive healing rates, consistent with nearby repeating microearthquakes. Finally, we document higher friction coefficients (μ > 0.4) and complex rate‐dependent behavior for samples recovered across the NBF. In total, our data provide an integrated view of fault behavior for the three active fault strands encountered at SAFOD and offer a consistent explanation for observations of creep and microearthquakes along weak fault zones within a strong crust.

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Section: 1002/2015jb011963mentioning

confidence: 99%

Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

2015

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“…Geodetic measurements reveal a permanent displacement rate of about 28 mm/year at its maximum over a narrow zone of less than 20 m (Titus et al, 2006). Bore hole drilling through the SAF allowed to correlate fault rock microstructures with real time geophysical data and therefore provides useful information to identify aseismic mechanisms (Bradbury et al, 2011;Holdsworth et al, 2011;Schleicher et al, 2009;Solum et al, 2006;Zoback et al, 2010).…”

Section: -Steady State Pressure Solution Creep Law: Modelling An Aseimentioning

confidence: 99%

The Role of Pressure Solution Creep in the Ductility of the Earth’s Upper Crust

Gratier

Dysthe

Renard

2013

Advances in Geophysics

248

274

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The aim of this review is to characterize the role of pressure solution creep in the ductility of the Earth's upper crust and to describe how this creep mechanism competes and interacts with other deformation mechanisms. Pressure solution creep is a major mechanism of ductile deformation of the upper crust, accommodating basin compaction, folding, shear zone development, and fault creep and interseismic healing. However, its kinetics is strongly dependent on the composition of the rocks (mainly the presence of phyllosilicates minerals that activate pressure solution) and on its interaction with fracturing and healing processes (that activate and slow down pressure solution, respectively).The present review combines three approaches: natural observations, theoretical developments, and laboratory experiments. Natural observations can be used to identify the pressure solution markers necessary to evaluate creep law parameters, such as the nature of the material, the temperature and stress conditions or the geometry of mass transfer domains. Theoretical developments help to investigate the thermodynamics and kinetics of the processes and to build theoretical creep laws.Laboratory experiments are implemented in order to test the models and to measure creep law parameters such as driving forces and kinetic coefficients. Finally, applications are discussed for the modelling of sedimentary basin compaction and fault creep. The sensitivity of the models to time is given particular attention: viscous versus plastic rheology during sediment compaction; steady state versus non-steady state behaviour of fault and shear zones. The conclusions discuss recent advances for modelling pressure solution creep and the main questions that remain to be solved. -IntroductionIn order to investigate the role of pressure solution creep in the ductility of the Earth's upper crust the various mechanical behaviour patterns of the upper crust must first be discussed. Two types of approach can be considered on this topic.1 -The mechanical behaviour of the upper crust is modelled using brittle theories, that include friction laws (Byerlee, 1978;Marone, 1998). This modelling approach is supported by two kinds of observations: (i) the maximum frequency of earthquakes is located within the first 15-20 km of the upper crust (Chen and Molnar, 1983;Sibson, 1982); (ii) laboratory experiments run at relatively fast strain-rates (faster than 10 -7 s -1 ) indicate a transition from frictional to plastic deformation at pressure and temperature conditions appropriate for a depth of 10-20 km (Kohlstedt et al., 1995;Paterson, 1978;Poirier, 1985).2 -Conversely, the behaviour of the upper crust is also modelled by ductile behaviour with creep laws (Wheeler, 1992). This modelling approach is supported by two kinds of observations: (i) geological structures exhumed from depth, such as compacted basin, folds and shear zones, and regional cleavage, indicate ductile behaviour throughout the upper crust (Argand, 1924;Hauck et al., 1998;Schmidt et al., 1996) (Fig. ...

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“…Many previous studies suggest that the growth of Mg-rich phyllosilicates may play a key role in the mechanical behavior of the SAF and can be directly related to fault weakening (e.g. Rymer, 2007, 2012;Schleicher et al, 2010;Holdsworth et al, 2011;Bradbury et al, 2011;Lockner et al, 2011). Janssen et al (2011) suggest that the presence of abundant clay minerals is often related to the occurrence of nanoscale porosity that may indicates high fluid pressure.…”

Section: Fault Rock Compositionmentioning

confidence: 99%

“…Detailed descriptions of SAFOD Phase 3 core material from Holes E and G (Fig. 1c) are given by Bradbury et al (2011), Holdsworth et al (2011), Hadizadeh et al (2012, and the SAFOD Core Photo Atlas (2010). The temperature at the depths of Hole G core recovery (2.65e2.7 km vertical depth) was 110e115 C compare also Schleicher et al, 2009).…”

Section: The Safod Projectmentioning

confidence: 99%

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Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

Janssen

Wirth

Wenk

et al. 2014

Journal of Structural Geology

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a b s t r a c tThe microstructures, mineralogy and chemistry of representative samples collected from the cores of the San Andreas Fault drill hole (SAFOD) and the Taiwan Chelungpu-Fault Drilling project (TCDP) have been studied using optical microscopy, TEM, SEM, XRD and XRF analyses. SAFOD samples provide a transect across undeformed host rock, the fault damage zone and currently active deforming zones of the San Andreas Fault. TCDP samples are retrieved from the principal slip zone (PSZ) and from the surrounding damage zone of the Chelungpu Fault. Substantial differences exist in the clay mineralogy of SAFOD and TCDP fault gouge samples. Amorphous material has been observed in SAFOD as well as TCDP samples. In line with previous publications, we propose that melt, observed in TCDP black gouge samples, was produced by seismic slip (melt origin) whereas amorphous material in SAFOD samples was formed by comminution of grains (crush origin) rather than by melting. Dauphiné twins in quartz grains of SAFOD and TCDP samples may indicate high seismic stress. The differences in the crystallographic preferred orientation of calcite between SAFOD and TCDP samples are significant. Microstructures resulting from dissolutioneprecipitation processes were observed in both faults but are more frequently found in SAFOD samples than in TCDP fault rocks. As already described for many other fault zones clay-gouge fabrics are quite weak in SAFOD and TCDP samples. Clay-clast aggregates (CCAs), proposed to indicate frictional heating and thermal pressurization, occur in material taken from the PSZ of the Chelungpu Fault, as well as within and outside of the SAFOD deforming zones, indicating that these microstructures were formed over a wide range of slip rates.

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Lithology and internal structure of the San Andreas fault at depth based on characterization of Phase 3 whole-rock core in the San Andreas Fault Observatory at Depth (SAFOD) borehole

Cited by 63 publications

References 76 publications

Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

The Role of Pressure Solution Creep in the Ductility of the Earth’s Upper Crust

Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

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