Effects of sample preparation on the microstructural signatures of faulting in clay-bearing fault gouge

Aiyama, Kotaro; Mizoguchi, Kazuo; Hirano, Kohei; Takizawa, Shigeru

doi:10.1016/j.jsg.2019.06.001

Cited by 6 publications

(1 citation statement)

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“…After the single velocity experiments, the sheared gouges were dried out in an environmental chamber and impregnated with a low viscosity epoxy resin. Most microstructures may be disturbed by the drying methodology (i.e., shrinkage may occur) either or after shear deformation (Aiyama et al., 2019). The impregnated samples were prepared into 30 μm thick petrographic thin sections, cut across the diameter of the sample and perpendicular to the slip surface.…”

Section: Methodsmentioning

confidence: 99%

Frictional Properties of the Longmenshan Fault Belt Gouges From WFSD‐3 and Implications for Earthquake Rupture Propagation

Kuo

Hung

et al. 2022

JGR Solid Earth

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The 2008 Mw 7.9 Wenchuan earthquake generated ∼270 and ∼80 km long surface ruptures along the Longmenshan fault belt, namely the Yingxiu‐Beichuan fault (YBF) and the Guanxian‐Anxian faults (GAF), respectively. So far, most of the frictional investigations were performed on the YBF gouge materials. Here, we present the results of rotary shear friction experiments performed on the GAF gouges recovered from the depth of ∼1.25 km of the Wenchuan Earthquake Fault Scientific Drilling project‐3 along the GAF. The fault gouges, mainly composed of quartz, illite, chlorite, and kaolinite, were sheared at slip velocities V ranging from 10−5 to 2 m/s and normal stresses from 8.5 to 10 MPa under both room humidity and wet conditions. At any imposed slip velocity, the wet gouges have an apparent friction coefficient lower than the room humidity one. In addition, enhanced velocity‐strengthening behavior at intermediate velocities (10−2 m/s < V ≤ 10−1 m/s) was recognized. We characterized the products using field‐emission scanning electron microscopy combined with synchrotron X‐ray diffraction analysis. These microanalytical investigations evidence the formation of size‐reduced particles (without mineral phase changes) and R‐ and Y‐shears in the principal slip zone (PSZ). Regardless of the ambient conditions, the width of PSZ was proportional to the input frictional work density (the product of shear stress times displacement). Our results support the hypothesis that the GAF preferentially ruptures through wet fault gouges; however, the enhanced velocity‐strengthening regime at intermediate velocities may act as a barrier to slip acceleration during fault rupture propagation.

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Section: Methodsmentioning

confidence: 99%