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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

Normal stress dependence on (a) nominal steady state and minimum friction values (LIZ gouge), (b) thermal weakening distance, and (c) the falloff velocity for multiple-velocity step and single-velocity step experiments. Run numbers are indicated in parentheses.
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fig04: Normal stress dependence on (a) nominal steady state and minimum friction values (LIZ gouge), (b) thermal weakening distance, and (c) the falloff velocity for multiple-velocity step and single-velocity step experiments. Run numbers are indicated in parentheses.

Mentions: The results of all single-velocity step experiments are reported in Table 1 and illustrated in Figure 3. In general, these experiments demonstrated similar differences between the behavior of bare surfaces and gouge observed in the multiple-velocity step experiments. In addition, because the velocity was held constant and normal stress was varied, we were able to explore the normal stress dependence on μnss, Dth, and Vf (compiled in Figure 4).


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)

Normal stress dependence on (a) nominal steady state and minimum friction values (LIZ gouge), (b) thermal weakening distance, and (c) the falloff velocity for multiple-velocity step and single-velocity step experiments. Run numbers are indicated in parentheses.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig04: Normal stress dependence on (a) nominal steady state and minimum friction values (LIZ gouge), (b) thermal weakening distance, and (c) the falloff velocity for multiple-velocity step and single-velocity step experiments. Run numbers are indicated in parentheses.
Mentions: The results of all single-velocity step experiments are reported in Table 1 and illustrated in Figure 3. In general, these experiments demonstrated similar differences between the behavior of bare surfaces and gouge observed in the multiple-velocity step experiments. In addition, because the velocity was held constant and normal stress was varied, we were able to explore the normal stress dependence on μnss, Dth, and Vf (compiled in Figure 4).

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