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  • 1
    Electronic Resource
    Electronic Resource
    Implications of Coulomb plasticity for the velocity dependence of experimental faults (1995)
    Springer
    Pure and applied geophysics 144 (1995), S. 251-276 
    Details
    ISSN: 1420-9136
    Keywords: Friction ; fault gouge ; fault mechanics ; Riedel shear ; earthquakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Simulated fault gouges often deform more stably than initially bare surfaces of the same composition. It is important to understand why the sliding stability is enhanced because the presence of gouge on natural faults may have the same effect as seen in experiments, and thus explain the absence of earthquakes at shallow depths. Gouge stabilization in experiments has been attributed to positive contributions to velocity dependence within gouge layers from either dilation (Marone et al., 1990) or grain fracture (Biegel et al., 1989). In this study we test the hypothesis that some aspects of gouge and initially bare surface velocity dependence are identical by measuring the time-dependent constitutive parameterb. An important result follows however from stress analysis: if both sample configurations are frictional in the Mohr-Coulomb sense, each configuration is required to deform on planes of distinctly different orientation. The measured strength and velocity dependence will reflect this geometric difference. Our observed values ofb for simulated granite and quartz gouge are two to two and a half times smaller thanb for initially bare surfaces. This difference is completely accounted for if gouge is represented as a cohesionless-Coulomb plastic material. The analysis demonstrates the following points: 1) gouge deformation is fully consistent with Coulomb plasticity, 2) observed gouge velocity dependence is a function of observed strength and 3) the constitutive parameterb is the same for both bare surfaces and gouge. Furthermore, the results suggest that there is no time-dependent strengthening associated with stabilizing effects in gouge. These observations provide a framework for understanding how slip on initially bare surfaces and gouge deformation are related.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878634
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  • 2
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    Direct Evidence for Fluid Pressure, Dilatancy, and Compaction Affecting Slip in Isolated Faults (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-08-12
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 3
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    A Robust Calibration Technique for Acoustic Emission Systems Based on Momentum Transfer from a Ball Drop (2015)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2015-01-30
    Description: We describe a technique to estimate the seismic moment of acoustic emissions and other extremely small seismic events. Unlike previous calibration techniques, it does not require modeling of the wave propagation, sensor response, or signal conditioning. Rather, this technique calibrates the recording system as a whole and uses a ball impact as a reference source or empirical Green’s function. To correctly apply this technique, we develop mathematical expressions that link the seismic moment M 0 of internal seismic sources (i.e., earthquakes and acoustic emissions) to the impulse, or change in momentum p , of externally applied seismic sources (i.e., meteor impacts or, in this case, ball impact). We find that, at low frequencies, moment and impulse are linked by a constant, which we call the force-moment-rate scale factor . This constant is equal to twice the speed of sound in the material from which the seismic sources were generated. Next, we demonstrate the calibration technique on two different experimental rock mechanics facilities. The first example is a saw-cut cylindrical granite sample that is loaded in a triaxial apparatus at 40 MPa confining pressure. The second example is a 2 m long fault cut in a granite sample and deformed in a large biaxial apparatus at lower stress levels. Using the empirical calibration technique, we are able to determine absolute source parameters including the seismic moment, corner frequency, stress drop, and radiated energy of these magnitude –2.5 to –7 seismic events.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 4
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    Faulting within the Mount St. Helens conduit and implications for volcanic earthquakes (2013)
    Geological Society of America (GSA)
    Details
    Publication Date: 2013-02-28
    Description: The 2004–2008 eruption of Mount St. Helens produced seven dacite spines mantled by cataclastic fault rocks, comprising an outer fault core and an inner damage zone. These fault rocks provide remarkable insights into the mechanical processes that accompany extrusion of degassed magma, insights that are useful in forecasting dome-forming eruptions. The outermost part of the fault core consists of finely comminuted fault gouge that is host to 1- to 3-mm-thick layers of extremely fine-grained slickenside-bearing ultracataclasite. Interior to the fault core, there is an ~2-m-thick damage zone composed of cataclastic breccia and sheared dacite, and interior to the damage zone, there is massive to flow-banded dacite lava of the spine interior. Structures and microtextures indicate entirely brittle deformation, including rock breakage, tensional dilation, shearing, grain flow, and microfaulting, as well as gas and fluid migration through intergranular pores and fractures in the damage zone. Slickenside lineations and consistent orientations of Riedel shears indicate upward shear of the extruding spines against adjacent conduit wall rocks. Paleomagnetic directions, demagnetization paths, oxide mineralogy, and petrology indicate that cataclasis took place within dacite in a solidified steeply dipping volcanic conduit at temperatures above 500 °C. Low water content of matrix glass is consistent with brittle behavior at these relatively high temperatures, and the presence of tridymite indicates solidification depths of 〈1 km. Cataclasis was coincident with the eruption’s seismogenic zone at 〈1.5 km. More than a million small and low-frequency "drumbeat" earthquakes with coda magnitudes (M d ) 〈2.0 and frequencies 〈5 Hz occurred during the 2004–2008 eruption. Our field data provide a means with which to estimate slip-patch dimensions for shear planes and to compare these with estimates of slip patches based on seismic moments and shear moduli for dacite rock and granular fault gouge. Based on these comparisons, we find that aseismic creep is achieved by micron-scale displacements on Riedel shears and by granular flow, whereas the drumbeat earthquakes require millimeter to centimeter displacements on relatively large (e.g., ~1000 m 2 ) slip patches, possibly along observed extensive principal shear zones within the fault core but probably not along the smaller Riedel shears. Although our field and structural data are compatible with stick-slip models, they do not rule out seismic and infrasound models that call on resonance of steam-filled fractures to generate the drumbeat earthquakes. We suggest that stick-slip and gas release processes may be coupled, and that regardless of the source mechanism, the distinctive drumbeat earthquakes are proving to be an effective precursor for dome-forming eruptions. Our data document a continuous cycle of deformation along the conduit margins beginning with episodes of fracture in the damage zone and followed by transfer of motion to the fault core. We illustrate the cycle of deformation using a hypothetical cross section of the Mount St. Helens conduit, extending from the surface to the depth of magmatic solidification.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 5
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    Re-Estimated Effects of Deep Episodic Slip on the Occurrence and Probability of Great Earthquakes in Cascadia (2014)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2014-02-04
    Description: Mazzotti and Adams (2004) estimated that rapid deep slip during typically two week long episodes beneath northern Washington and southern British Columbia increases the probability of a great Cascadia earthquake by 30–100 times relative to the probability during the ~58 weeks between slip events. Because the corresponding absolute probability remains very low at ~0.03% per week, their conclusion is that though it is more likely that a great earthquake will occur during a rapid slip event than during other times, a great earthquake is unlikely to occur during any particular rapid slip event. This previous estimate used a failure model in which great earthquakes initiate instantaneously at a stress threshold. We refine the estimate, assuming a delayed failure model that is based on laboratory-observed earthquake initiation. Laboratory tests show that failure of intact rock in shear and the onset of rapid slip on pre-existing faults do not occur at a threshold stress. Instead, slip onset is gradual and shows a damped response to stress and loading rate changes. The characteristic time of failure depends on loading rate and effective normal stress. Using this model, the probability enhancement during the period of rapid slip in Cascadia is negligible (〈10%) for effective normal stresses of 10 MPa or more and only increases by 1.5 times for an effective normal stress of 1 MPa. We present arguments that the hypocentral effective normal stress exceeds 1 MPa. In addition, the probability enhancement due to rapid slip extends into the interevent period. With this delayed failure model for effective normal stresses greater than or equal to 50 kPa, it is more likely that a great earthquake will occur between the periods of rapid deep slip than during them. Our conclusion is that great earthquake occurrence is not significantly enhanced by episodic deep slip events.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 6
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    Earthquake Source Properties from Pseudotachylite (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-12-02
    Description: Earthquake-radiated motions contain information that can be interpreted as source displacement and therefore related to stress drop. Except in a few notable cases, these displacements cannot be easily related to the absolute stress level or the fault strength, or attributed to a particular physical mechanism. In contrast, paleoearthquakes recorded by exhumed pseudotachylite have a known dynamic mechanism whose properties constrain the coseismic fault strength. Pseudotachylite can be used to directly address a discrepancy between seismologically measured stress drops, which are typically a few MPa, and much larger dynamic stress drops expected from thermal weakening during slip at seismic speeds in crystalline rock ( Mckenzie and Brune, 1972 ; Sibson, 1973 ; Lachenbruch, 1980 ; Mase and Smith, 1987 ; Rice, 2006 ), and as have been observed in laboratory experiments at high slip rates ( Di Toro, Hirose, Nielsen, Pennacchioni, et al. , 2006 ). This places pseudotachylite-derived estimates of fault strength and inferred crustal stress within the context and bounds of naturally observed earthquake source parameters: apparent stress, stress drop, and overshoot, including consideration of fault-surface roughness, off-fault damage, fracture energy, and the strength excess. The analysis, which assumes stress drop is related to corner frequency as in the Madariaga (1976) source model, is restricted to earthquakes of the Gole Larghe fault zone in the Italian Alps, where the dynamic shear strength is well constrained by field and laboratory measurements. We find that radiated energy is similar to or exceeds the shear-generated heat and that the maximum strength excess is ~16 MPa. These events have inferred earthquake source parameters that are rare, for instance, a low percentage of the global earthquake population has stress drops as large, unless fracture energy is routinely greater than in existing models, pseudotachylite is not representative of the shear strength during the earthquake that generated it, or the strength excess is larger than we have allowed.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 7
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    The role of fluid pressure on frictional behavior at the base of the seismogenic zone (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-02-25
    Description: To characterize stress and deformation style at the base of the seismogenic zone, we investigate how the mechanical properties of fluid-rock systems respond to variations in temperature and strain rate. The role of fluids on the processes responsible for the brittle-ductile transition in quartz-rich rocks has not been explored at experimental conditions where the kinetic competition between microcracking and viscous flow is similar to that expected in the Earth. Our initial analysis of this competition suggests that the effective stress law for sliding friction should not work as efficiently near the brittle-ductile transition as it does at shallow conditions.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Using Low-Frequency Earthquake Families on the San Andreas Fault as Deep Creepmeters (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-01-01
    Description: The central section of the San Andreas Fault hosts tectonic tremor and low-frequency earthquakes (LFEs) similar to subduction zone environments. LFEs are often interpreted as persistent regions that repeatedly fail during the aseismic shear of the surrounding fault allowing them to be used as creepmeters. We test this idea by using the recurrence intervals of individual LFEs within LFE families to estimate the timing, duration, recurrence interval, slip, and slip rate associated with inferred slow slip events. We formalize the definition of a creepmeter and determine whether this definition is consistent with our observations. We find that episodic families reflect surrounding creep over the interevent time, while the continuous families and the short time scale bursts that occur as part of the episodic families do not. However, when these families are evaluated on time scales longer than the interevent time these events can also be used to meter slip. A straightforward interpretation of episodic families is that they define sections of the fault where slip is distinctly episodic in well-defined slow slip events that slip 16 times the long-term rate. In contrast, the frequent short-term bursts of the continuous and short time scale episodic families likely do not represent individual creep events but rather are persistent asperities that are driven to failure by quasi-continuous creep on the surrounding fault. Finally, we find that the moment-duration scaling of our inferred creep events are inconsistent with the proposed linear moment-duration scaling. However, caution must be exercised when attempting to determine scaling with incomplete knowledge of scale. ©2017. American Geophysical Union. All Rights Reserved.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 9
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    Constraints on Friction, Dilatancy, Diffusivity, and Effective Stress From Low-Frequency Earthquake Rates on the Deep San Andreas Fault (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-01-01
    Description: Families of recurring low-frequency earthquakes (LFEs) within nonvolcanic tremor on the San Andreas Fault in central California are sensitive to tidal stresses. LFEs occur at all levels of the tides, are strongly correlated and in phase with the ~200 Pa shear stresses, and weakly and not systematically correlated with the ~2 kPa tidal normal stresses. We assume that LFEs are small sources that repeatedly fail during shear within a much larger scale, aseismically slipping fault zone and consider two different models of the fault slip: (1) modulation of the fault slip rate by the tidal stresses or (2) episodic slip, triggered by the tides. LFEs are strongly clustered with duration much shorter than the semidiurnal tide; they cannot be significantly modulated on that time scale. The recurrence times of clusters, however, are many times longer than the semidiurnal, leading to an appearance of tidal triggering. In this context we examine the predictions of laboratory-observed triggered frictional (dilatant) fault slip. The undrained end-member model produces no sensitivity to the tidal normal stress, and slip onsets are in phase with the tidal shear stress. The tidal correlation constrains the diffusivity to be less than ~1 × 10−6/s and the product of the friction and dilatancy coefficients to be at most 5 × 10−7, orders of magnitude smaller than observed at room temperature. In the absence of dilatancy the effective normal stress at failure would be about ~55 kPa. For this model the observations require intrinsic weakness, low dilatancy, and lithostatic pore fluid. ©2017. American Geophysical Union. All Rights Reserved.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 10
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    On the Depth Extent of Coseismic Rupture (2018)
    Seismological Society of America
    Details
    Publication Date: 2018-02-13
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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