Magnitude of Shear Stress on the San Andreas Fault: Implications of a Stress Measurement Profile at Shallow Depth

Zoback, Mark D.; Roller, John C.

doi:10.1126/science.206.4417.445

Cited by 36 publications

(18 citation statements)

References 8 publications

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“…We know from surface exposures that fault gouge of various compositions occurs along active tectonic faults (e.g., the San Andreas Fault). There is a discrepancy between the shear stress required to initiate rock-on-rock sliding and the shear stress on the San Andreas fault and other active tectonic areas (Zoback and Roller 1979). Early laboratory studies (Velde 1969) showed that kaolinite and montmorillonite form a stable mineral assemblage at pressures up to 3.5 GPa and temperatures below 420 ∞C.…”

Section: Introductionmentioning

confidence: 98%

Pressure-controlled polytypism in hydrous layered materials

Dera

Prewitt

Japel

et al. 2003

American Mineralogist

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An isosymmetric displacive structural transformation in the hydrous layer silicate dickite [Al 2 Si 2 O 5 (OH) 4 , monoclinic Cc, a = 5.161(3), b = 8.960(6), c = 14.459(10) Å, b = 96.77(1)∞], occurring under hydrostatic compression above 2.0 GPa, has been studied using single-crystal X-ray diffraction and diamond-anvil cell techniques. The structure of the high-pressure phase, determined in situ, is monoclinic with space group Cc with unit-cell parameters a = 5.082(3), b = 8.757 (6), c = 13.771(9) Å, and b = 89.60(2)∞ at 4.1 GPa. The positions of all hydrogen atoms at both ambient and high pressure have been determined by a combination of simulated annealing and energy minimization. The mechanism of the transformation, which may be general for other hydrous layered materials, involves a shift of the 1:1 layers with respect to each other by the vector [1/6, 1/6, 0] and is accompanied by the formation of new hydrogen bonds.

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Section: Introductionmentioning

confidence: 98%

Pressure-controlled polytypism in hydrous layered materials

Dera

Prewitt

Japel

et al. 2003

American Mineralogist

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“…Accordingly, the hydraulic fracturing technique was used to make stress measurements in wells ~230 m in depth that were drilled along profiles roughly perpendicular to the fault; one profile was located in the western Mojave desert near Palmdale, where the San Andreas has been locked since the 1857 great earthquake, and the other profile was located in the Gabilan range of central California, where aseismic creep and small magnitude earthquakes characterize the fault's behavior. The Mojave profile data were briefly discussed by Zoback and Roller [1979]. Second, we measured the variation of shear stress with depth in a ~ 1-km-deep hole that was drilled at one of the sites of the Mojave profile located about 4 km from the fault.…”

Section: Introductionmentioning

confidence: 99%

Stress measurements at depth in the vicinity of the San Andreas Fault: Implications for the magnitude of shear stress at depth

Zoback¹,

Tsukahara²,

Hickman³

1980

J. Geophys. Res.

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154

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“…In this field, one of the most exciting developments in the last few years has been the systematic measurement of in situ stresses using the hydrofrac technique at depths of the order of several hundred meters along horizontal profiles in the vicinity of the San Andreas fault, California [Zoback and Roller, 1979;Keys et al, 1979]. The study by Keys et al in central California was not entirely successful, because the shale formation in which they made their measurements appeared to be too weak to retain substantial deviatoric stresses.…”

Section: Introductionmentioning

confidence: 99%

Some constraints on levels of shear stress in the crust from observations and theory

McGarr¹

1980

J. Geophys. Res.

116

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In situ stress determinations in North America, southern Africa, and Australia indicate that on the average the maximum shear stress increases linearly with depth to at least 5.1 km measured in soft rock, such as shale and sandstone, and to 3.7 km in hard rock, including granite and quartzite. Regression lines fitted to the data yield gradients of 3.8 MPa/km and 6.6 MPa/km for soft and hard rock, respectively. Generally, the maximum shear stress in compressional states of stress for which the least principal stress is oriented near vertically is substantially greater than in extensional stress regimes, with the greatest principal stress in a vertical direction. The equations of equilibrium and compatibility can be used to provide functional constraints on the state of stress. If the stress is assumed to vary only with depth z in a given region, then all nonzero components must have the form A+Bz, where A and B are constants which generally differ for the various components. This implies that the deviatoric stress changes linearly with depth, and the general solution also allows the directions of the horizontal principal stresses to change monotonically with depth. Solutions to the equations, a churning stress to vary with both z and x, were fit to the observations of Zoback and Roller, who measured stress along a horizontal profile near Palmdale, California. The results indicate that the average shear stress in the upper 8 km of the fault zone is about 3.5 MPa less than the shear stress in the far field, but this far field term, which is part of the solution and has the form A+Bz, cannot be evaluated using the existing constant depth data.

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Magnitude of Shear Stress on the San Andreas Fault: Implications of a Stress Measurement Profile at Shallow Depth

Cited by 36 publications

References 8 publications

Pressure-controlled polytypism in hydrous layered materials

Pressure-controlled polytypism in hydrous layered materials

Stress measurements at depth in the vicinity of the San Andreas Fault: Implications for the magnitude of shear stress at depth

Some constraints on levels of shear stress in the crust from observations and theory

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