Evolution of ultrasonic velocity and dynamic elastic moduli with shear strain in granular layers

Knuth, M.; Tobin, H. J.; Marone, Chris

doi:10.1007/s10035-013-0420-1

Cited by 38 publications

(59 citation statements)

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“…There is a similar difference in stress‐strain evolution as a function of composition. Smectite‐rich samples (≥50 wt%) exhibit a peak friction and subsequent decay at shear strains of ~1–2, whereas smectite‐poor samples exhibit a roll over in friction after initial loading and simply approach a steady‐state value (Figure 3a) (Haines et al, 2013; Ikari et al, 2009; Knuth et al, 2013; Logan & Rauenzahn, 1987; Saffer & Marone, 2003). The natural samples—with high clay contents (~50% smectite + illite)—behave more similarly to the low clay synthetic gouges.…”

Section: Resultsmentioning

confidence: 99%

“…Like the smectite‐rich gouges, these materials exhibit a peak in wave speeds at shear strains of ~2 followed by a reduction in these quantities up to a shear strain of ~6, beyond which Vp , Vs , and elastic moduli all increase. As shear initiates, Riedel and P‐shears form first and are not pervasive enough nor are they oriented in a way that they would interfere with wave propagation (Fortin et al, 2007; Haines et al, 2013; Kaproth & Marone, 2014; Khidas & Jia, 2012; Knuth et al, 2013). As shear progresses, Y‐shears form, and Riedel shears begin to rotate subparallel to the direction of shear (often becoming Y‐shears) and perpendicular to the direction of wave propagation (Haines et al, 2013; Logan et al, 1992; Logan & Rauenzahn, 1987).…”

Section: Discussionmentioning

confidence: 99%

“…Using these velocities together with bulk densities defined by our mass loss model, we compute elastic moduli throughout shear (Digby, 1981; Kaproth & Marone, 2014; Knuth et al, 2013):

G = ρ V_{s}^{2}

K = {ρV}_{p}^{2} - \frac{4}{3} G

where K is bulk modulus and G is shear modulus.…”

Section: Methodsmentioning

confidence: 99%

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Evolution of Elastic and Mechanical Properties During Fault Shear: The Roles of Clay Content, Fabric Development, and Porosity

et al. 2020

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Phyllosilicates weaken faults due to the formation of shear fabrics. Although the impacts of clay abundance and fabric on frictional strength, sliding stability, and porosity of faults are well studied, their influence on elastic properties is less known, though they are key factors for fault stiffness. We document the role that fabric and consolidation play in elastic properties and show that smectite content is the most important factor determining whether fabric or porosity controls the elastic response of faults. We conducted a suite of shear experiments on synthetic smectite‐quartz fault gouges (10–100 wt% smectite) and sediment incoming to the Sumatra subduction zone. We monitored Vp, Vs, friction, porosity, shear and bulk moduli. We find that mechanical and elastic properties for gouges with abundant smectite are almost entirely controlled by fabric formation (decreasing mechanical and elastic properties with shear). Though fabrics control the elastic response of smectite‐poor gouges over intermediate shear strains, porosity is the primary control throughout the majority of shearing. Elastic properties vary systematically with smectite content: High smectite gouges have values of Vp ~ 1,300–1,800 m/s, Vs ~ 900–1,100 m/s, K ~ 1–4 GPa, and G ~ 1–2 GPa, and low smectite gouges have values of Vp ~ 2,300–2,500 m/s, Vs ~ 1,200–1,300 m/s, K ~ 5–8 GPa, and G ~ 2.5–3 GPa. We find that, even in smectite‐poor gouges, shear fabric also affects stiffness and elastic moduli, implying that while smectite abundance plays a clear role in controlling gouge properties, other fine‐grained and platy clay minerals may produce similar behavior through their control on the development of fabrics and thin shear surfaces.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Evolution of Elastic and Mechanical Properties During Fault Shear: The Roles of Clay Content, Fabric Development, and Porosity

et al. 2020

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“…In Figure 3, we provide one example illustrating these combined effects of friction rate dependence, the characteristic slip distance D c , and loading system stiffness, K. We consider a subduction zone example, parameterized with laboratory-derived friction data from clay and clay-quartz mixtures analogous to natural fault gouge (Ikari et al, 2007), with the effective stiffness of the loading system defined by elastic constants measured for subduction zone sediments over a wide range of stresses (Gettemy and Tobin, 2003;Knuth et al, 2013). In Figure 3, we provide one example illustrating these combined effects of friction rate dependence, the characteristic slip distance D c , and loading system stiffness, K. We consider a subduction zone example, parameterized with laboratory-derived friction data from clay and clay-quartz mixtures analogous to natural fault gouge (Ikari et al, 2007), with the effective stiffness of the loading system defined by elastic constants measured for subduction zone sediments over a wide range of stresses (Gettemy and Tobin, 2003;Knuth et al, 2013).…”

Section: Repetitive Frictional Failure and The Upper Stability Transimentioning

confidence: 99%

The Mechanics of Frictional Healing and Slip Instability During the Seismic Cycle

Marone

Saffer

2015

Treatise on Geophysics

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“…Knuth et al . [] showed that changes in P ‐wave speed and wave amplitude could be explained by changes in grain contact stiffness, crack density, and disruption of granular force chains, based on work by Jia et al . [].…”

Section: Introductionmentioning

confidence: 99%

On the evolution of elastic properties during laboratory stick‐slip experiments spanning the transition from slow slip to dynamic rupture

et al. 2016

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The physical mechanisms governing slow earthquakes remain unknown, as does the relationship between slow and regular earthquakes. To investigate the mechanism(s) of slow earthquakes and related quasi‐dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration. We reproduced the full spectrum of slip behavior, from slow to fast stick slip, by altering the elastic stiffness of the loading apparatus (k) to match the critical rheologic stiffness of fault gouge (kc). Our experiments show an evolution from stable sliding, when k > kc, to quasi‐dynamic transients when k ~ kc, to dynamic instabilities when k < kc. To evaluate the microphysical processes of fault weakening we monitored variations of elastic properties. We find systematic changes in P wave velocity (Vp) for laboratory seismic cycles. During the coseismic stress drop, seismic velocity drops abruptly, consistent with observations on natural faults. In the preparatory phase preceding failure, we find that accelerated fault creep causes a Vp reduction for the complete spectrum of slip behaviors. Our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults, depending on frictional properties. In agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by Vp changes during the seismic cycle. The observed reduction in Vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high‐resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors.

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Evolution of ultrasonic velocity and dynamic elastic moduli with shear strain in granular layers

Cited by 38 publications

References 100 publications

Evolution of Elastic and Mechanical Properties During Fault Shear: The Roles of Clay Content, Fabric Development, and Porosity

Evolution of Elastic and Mechanical Properties During Fault Shear: The Roles of Clay Content, Fabric Development, and Porosity

The Mechanics of Frictional Healing and Slip Instability During the Seismic Cycle

On the evolution of elastic properties during laboratory stick‐slip experiments spanning the transition from slow slip to dynamic rupture

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