Heat flow, stress, and rate of slip along the San Andreas Fault, California

Brune, James N.; Henyey, Thomas L.; Roy, Robert F.

doi:10.1029/jb074i015p03821

Cited by 431 publications

(244 citation statements)

References 14 publications

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“…On one hand direct laboratory measurements (STESKY and BRACE, 1973) and deep mine fracture experiments in intact rock (SPoTTIswooD and MCGARR, 1975) indicate that the shear stress at about 10 km is 1 to 2 kbars and that stress changes of up to 1 kbar should therefore accompany faulting. On the other hand an upper limit on the average shear stress on the fault of a few hundred bars is indicated by the absence of a detectable heat flow anomaly near the San Andreas fault (BRUNE et al, 1969;LACHENBRUCH and SASS, 1973). The mean displacement-to-length ratios far earthquakes that rupture the surface also indicate an average change in stress of about 100barS (CHINNERY and PETRAK, 1968).…”

Section: Introductionmentioning

confidence: 99%

Local magnetic field variations and stress changes near a slip discontinuity on the San Andreas fault.

Johnston

1978

J. geomagn. geoelec

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Data from an array of proton magnetometers in central California indicate that a systematic decrease in magnetic field of about 21 in 5 years has occurred in a localized region near Anzar, California, just north of the creeping section of the San Andreas fault. This field change has most likely resulted from changes in crustal stress in this region, although an unknown second-order effect of secular variation cannot be excluded as a alternate explanation. Tectonomagnetic models have been developed using dislocation modeling of slip on a finite section of fault. Assuming a fault geometry and rock magnetization, these models relate changes in stress, fault slip, and fault geometry to surface magnetic field anomalies. A large-scale anomaly, opposite in sense to that observed but of similar amplitude, would be expected to have accumulated in this area during the past 70 years. A localized 5-bar decrease in shear strain on the fault resulting from about 2 cm of slip on a 0.25-km square patch at a depth of 1 km beneath the surface trace of the fault opposite the magnetometer could explain the observed data and still be compatible with the geodetic strain measurements in the area. Other models of limited local slip are equally possible. The occurrence of a moderate magnitude earthquake in this region will allow comparison of stress changes estimated by different techniques.

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Section: Introductionmentioning

confidence: 99%

Local magnetic field variations and stress changes near a slip discontinuity on the San Andreas fault.

Johnston

1978

J. geomagn. geoelec

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“…These initiatives have recovered samples of fault rock and gouge and conducted measurements of in situ stress, fluid chemistry, and temperature at depths where earthquakes nucleate. Samples and data emerging from these drilling projects provide an unparalleled opportunity to gain new insight into absolute fault strength [e.g., Brune et al, 1969;Zoback et al, 1987;Scholz, 2000;Carpenter et al, 2012], causes of apparent fault weakness [e.g., Rice, 1992;Faulkner and Rutter, 2001;Brantut et al, 2011;Gratier et al, 2011;Lockner et al, 2011], and the laws that govern fault slip and failure [e.g., Dieterich, 1979;Marone, 1998a;Ikari et al, 2009;Carpenter et al, 2011;Sone et al, 2012].…”

Section: Introductionmentioning

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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“…This magnitude of friction is hypothesized to generate large thermal anomalies on natural faults with large slip rates and/or large total displacements, assuming hydrostatic pore pressure. Curiously, analysis of surface heat flow data [e.g., Brune et al, 1969;Lachenbruch and Sass, 1980;Wang et al, 1995] and subsurface temperature profiles [Yamano and Goto, 2001;Kano et al, 2006;Tanaka et al, 2006Tanaka et al, , 2007 that cross fault zones do not show substantial, unequivocal anomalies from frictional heating. These observations prompt two questions: (1) could the frictional resistance be as large as expected from Byerlee's law and hydrostatic pore pressure, but the heat signal is masked or dissipated by other processes?…”

Section: Introductionmentioning

confidence: 99%

Does hydrologic circulation mask frictional heat on faults after large earthquakes?

et al. 2010

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[1] Knowledge of frictional resistance along faults is important for understanding the mechanics of earthquakes and faulting. The clearest in situ measure of fault friction potentially comes from temperature measurements in boreholes crossing fault zones within a few years of rupture. However, large temperature signals from frictional heating on faults have not been observed. Unambiguously interpreting the coseismic frictional resistance from small thermal perturbations observed in borehole temperature profiles requires assessing the impact of other potentially confounding thermal processes. We address several issues associated with quantifying the temperature signal of frictional heating including transient fluid flow associated with the earthquake, thermal disturbance caused by borehole drilling, and heterogeneous thermal physical rock properties. Transient fluid flow is investigated using a two-dimensional coupled fluid flow and heat transport model to evaluate the temperature field following an earthquake. Simulations for a range of realistic permeability, frictional heating, and pore pressure scenarios show that high permeabilities (>10 −14 m 2 ) are necessary for significant advection within the several years after an earthquake and suggest that transient fluid flow is unlikely to mask frictional heat anomalies. We illustrate how disturbances from circulating fluids during drilling diffuse quickly leaving a robust signature of frictional heating. Finally, we discuss the utility of repeated borehole temperature profiles for discriminating between different interpretations of thermal perturbations. Our results suggest that temperature anomalies from even low friction should be detectable at depths >1 km 1 to 2 years after a large earthquake and that interpretations of low friction from existing data are likely robust.Citation: Fulton, P. M., R. N. Harris, D. M. Saffer, and E. E. Brodsky (2010), Does hydrologic circulation mask frictional heat on faults after large earthquakes?,

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Heat flow, stress, and rate of slip along the San Andreas Fault, California

Cited by 431 publications

References 14 publications

Local magnetic field variations and stress changes near a slip discontinuity on the San Andreas fault.

Local magnetic field variations and stress changes near a slip discontinuity on the San Andreas fault.

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

Does hydrologic circulation mask frictional heat on faults after large earthquakes?

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