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Dynamic weakening of serpentinite gouges and bare surfaces at seismic slip rates.

Proctor BP, Mitchell TM, Hirth G, Goldsby D, Zorzi F, Platt JD, Di Toro G - J Geophys Res Solid Earth (2014)

Bottom Line: X-ray diffraction revealed dehydration reaction products in samples that frictionally weakened.Microstructural analysis revealed highly localized slip zones with melt-like textures in some cases gouge experiments and in all bare surfaces experiments for V ≥ 1 m/s.One-dimensional thermal modeling indicates that flash heating causes frictional weakening in both bare surfaces and gouge.

View Article: PubMed Central - PubMed

Affiliation: Department of Geological Sciences, Brown University Providence, Rhode Island, USA.

ABSTRACT

: To investigate differences in the frictional behavior between initially bare rock surfaces of serpentinite and powdered serpentinite ("gouge") at subseismic to seismic slip rates, we conducted single-velocity step and multiple-velocity step friction experiments on an antigorite-rich and lizardite-rich serpentinite at slip rates (V) from 0.003 m/s to 6.5 m/s, sliding displacements up to 1.6 m, and normal stresses (σn ) up to 22 MPa for gouge and 97 MPa for bare surfaces. Nominal steady state friction values (μ nss) in gouge at V = 1 m/s are larger than in bare surfaces for all σn tested and demonstrate a strong σn dependence; μ nss decreased from 0.51 at 4.0 MPa to 0.39 at 22.4 MPa. Conversely, μ nss values for bare surfaces remained ∼0.1 with increasing σn and V. Additionally, the velocity at the onset of frictional weakening and the amount of slip prior to weakening were orders of magnitude larger in gouge than in bare surfaces. Extrapolation of the normal stress dependence for μ nss suggests that the behavior of antigorite gouge approaches that of bare surfaces at σn ≥ 60 MPa. X-ray diffraction revealed dehydration reaction products in samples that frictionally weakened. Microstructural analysis revealed highly localized slip zones with melt-like textures in some cases gouge experiments and in all bare surfaces experiments for V ≥ 1 m/s. One-dimensional thermal modeling indicates that flash heating causes frictional weakening in both bare surfaces and gouge. Friction values for gouge decrease at higher velocities and after longer displacements than bare surfaces because strain is more distributed.

Key points: Gouge friction approaches that of bare surfaces at high normal stressDehydration reactions and bulk melting in serpentinite in < 1 m of slipFlash heating causes dynamic frictional weakening in gouge and bare surfaces.

No MeSH data available.


Related in: MedlinePlus

(a) Results from three multiple-velocity step experiments: 3 mm/s for ∼6 cm of displacement, acceleration to ∼4.5 m/s, and deceleration to rest. The approximate thermal-weakening distance (Dth) and slip-weakening distance (Dw) are indicated for Run 735 (see text for details). Stars indicate the displacement at which the friction rapidly decreases; the corresponding velocity (falloff velocity) is shown in Figure 2b. (b) Frictional stick-slip instabilities observed in Run 735 at 3 mm/s. (c) The imposed velocity profiles for experiments shown in Figure 2a. Note that the acceleration is very similar in both gouge and bare surface experiments.
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fig02: (a) Results from three multiple-velocity step experiments: 3 mm/s for ∼6 cm of displacement, acceleration to ∼4.5 m/s, and deceleration to rest. The approximate thermal-weakening distance (Dth) and slip-weakening distance (Dw) are indicated for Run 735 (see text for details). Stars indicate the displacement at which the friction rapidly decreases; the corresponding velocity (falloff velocity) is shown in Figure 2b. (b) Frictional stick-slip instabilities observed in Run 735 at 3 mm/s. (c) The imposed velocity profiles for experiments shown in Figure 2a. Note that the acceleration is very similar in both gouge and bare surface experiments.

Mentions: Results from all multiple-velocity step tests are reported in Table 1. Three representative experiments (Runs 705, 824b, and 735) are shown in Figure 2a. These tests illustrate differences between the frictional behavior of serpentine bare surfaces and serpentine gouge at subseismic and seismic slip velocities.


Dynamic weakening of serpentinite gouges and bare surfaces at seismic slip rates.

Proctor BP, Mitchell TM, Hirth G, Goldsby D, Zorzi F, Platt JD, Di Toro G - J Geophys Res Solid Earth (2014)

(a) Results from three multiple-velocity step experiments: 3 mm/s for ∼6 cm of displacement, acceleration to ∼4.5 m/s, and deceleration to rest. The approximate thermal-weakening distance (Dth) and slip-weakening distance (Dw) are indicated for Run 735 (see text for details). Stars indicate the displacement at which the friction rapidly decreases; the corresponding velocity (falloff velocity) is shown in Figure 2b. (b) Frictional stick-slip instabilities observed in Run 735 at 3 mm/s. (c) The imposed velocity profiles for experiments shown in Figure 2a. Note that the acceleration is very similar in both gouge and bare surface experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497455&req=5

fig02: (a) Results from three multiple-velocity step experiments: 3 mm/s for ∼6 cm of displacement, acceleration to ∼4.5 m/s, and deceleration to rest. The approximate thermal-weakening distance (Dth) and slip-weakening distance (Dw) are indicated for Run 735 (see text for details). Stars indicate the displacement at which the friction rapidly decreases; the corresponding velocity (falloff velocity) is shown in Figure 2b. (b) Frictional stick-slip instabilities observed in Run 735 at 3 mm/s. (c) The imposed velocity profiles for experiments shown in Figure 2a. Note that the acceleration is very similar in both gouge and bare surface experiments.
Mentions: Results from all multiple-velocity step tests are reported in Table 1. Three representative experiments (Runs 705, 824b, and 735) are shown in Figure 2a. These tests illustrate differences between the frictional behavior of serpentine bare surfaces and serpentine gouge at subseismic and seismic slip velocities.

Bottom Line: X-ray diffraction revealed dehydration reaction products in samples that frictionally weakened.Microstructural analysis revealed highly localized slip zones with melt-like textures in some cases gouge experiments and in all bare surfaces experiments for V ≥ 1 m/s.One-dimensional thermal modeling indicates that flash heating causes frictional weakening in both bare surfaces and gouge.

View Article: PubMed Central - PubMed

Affiliation: Department of Geological Sciences, Brown University Providence, Rhode Island, USA.

ABSTRACT

: To investigate differences in the frictional behavior between initially bare rock surfaces of serpentinite and powdered serpentinite ("gouge") at subseismic to seismic slip rates, we conducted single-velocity step and multiple-velocity step friction experiments on an antigorite-rich and lizardite-rich serpentinite at slip rates (V) from 0.003 m/s to 6.5 m/s, sliding displacements up to 1.6 m, and normal stresses (σn ) up to 22 MPa for gouge and 97 MPa for bare surfaces. Nominal steady state friction values (μ nss) in gouge at V = 1 m/s are larger than in bare surfaces for all σn tested and demonstrate a strong σn dependence; μ nss decreased from 0.51 at 4.0 MPa to 0.39 at 22.4 MPa. Conversely, μ nss values for bare surfaces remained ∼0.1 with increasing σn and V. Additionally, the velocity at the onset of frictional weakening and the amount of slip prior to weakening were orders of magnitude larger in gouge than in bare surfaces. Extrapolation of the normal stress dependence for μ nss suggests that the behavior of antigorite gouge approaches that of bare surfaces at σn ≥ 60 MPa. X-ray diffraction revealed dehydration reaction products in samples that frictionally weakened. Microstructural analysis revealed highly localized slip zones with melt-like textures in some cases gouge experiments and in all bare surfaces experiments for V ≥ 1 m/s. One-dimensional thermal modeling indicates that flash heating causes frictional weakening in both bare surfaces and gouge. Friction values for gouge decrease at higher velocities and after longer displacements than bare surfaces because strain is more distributed.

Key points: Gouge friction approaches that of bare surfaces at high normal stressDehydration reactions and bulk melting in serpentinite in < 1 m of slipFlash heating causes dynamic frictional weakening in gouge and bare surfaces.

No MeSH data available.


Related in: MedlinePlus