Seismic-frequency Laboratory Measurements of Shear Mode Viscoelasticity in Crustal Rocks II: Thermally Stressed Quartzite and Granite

Cao, Lu; Jackson, Ian

doi:10.1007/978-3-0348-8711-3_10

Cited by 6 publications

(8 citation statements)

References 52 publications

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“…The sample mass and mercury porosimetry‐measured porosity are used in conjunction with this measured envelope volume to calculate a grain density of 2,708 ± 7 kg/m 3 for the Cape Sorell quartzite; the Alberta sample is measured to have a grain density of 2,659 ± 7 kg/m 3 . The Cape Sorell results are ~2% different to the density of 2,637 kg/m 3 measured by Lu and Jackson () using Archimedes principle. This small discrepancy is likely indicative of local heterogeneity between the porosity or mineralogy of the Cape Sorell samples measured in the separate studies.…”

Section: Characterization Of Rock Specimenscontrasting

confidence: 76%

“…It is concluded that much of the porosity measured at ambient conditions on the thermally cracked quartzites is probably contributed by uniform partings of near‐zero aspect ratio (Figures d and d) expected to close at pressures <<10 MPa; cracks of significantly larger aspect ratio than 0.001 that remain open at the highest experimentally accessible pressure of 150 MPa, and account for the residual crack density, also contribute to the total porosity. Previous studies infer the Cape Sorell quartzite to have porosity with an initial aspect ratio of 0.02 (Lu & Jackson, ), which may remain an upper bound on the aspect ratio distribution for this quartzite after induced cracking. The larger crack density modeled in the Alberta quartzite than in the Cape Sorell quartzite at high pressures implies that the Alberta quartzite may have either a larger number or more equant, higher aspect ratio, cracks than the Cape Sorell sample.…”

Section: Discussionmentioning

confidence: 91%

“…Both quartzite specimens are dominated by quartz grains of ~0.5 mm diameter. The Cape Sorell specimen (Figure ) is a translucent light gray in appearance and has been shown to be more than 99% quartz by volume, with <1% muscovite at the grain boundaries (Lu & Jackson, ). X‐ray diffraction and SEM confirm that the Alberta quartzite, by comparison, is nearly entirely composed of quartz grains with a thin film of iron oxide at the grain boundaries (Figure ).…”

Section: Characterization Of Rock Specimensmentioning

confidence: 99%

“…Thin section images of the quartzites prior to any treatment showed that they initially did not have significant crack porosity (Figures and ); saturating with distilled water in a vacuum gave an initial porosity of 0.3% in the Cape Sorell quartzite (Lu & Jackson, ), and mercury porosimetry measured 0.8% initial porosity in the Alberta quartzite. In order to increase the crack porosity and thereby the potential dispersion, it was necessary to induce additional cracks into these materials.…”

Section: Characterization Of Rock Specimensmentioning

confidence: 99%

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Shear Modulus Dispersion in Cracked and Fluid‐Saturated Quartzites: Experimental Observations and Modeling

2018

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The effect of pore fluids on acoustic wave dispersion in rocks with low aspect ratio crack porosity is important for the interpretation of laboratory and field observations in hard rock mineral exploration environments. Here we make laboratory measurements of shear modulus dispersion at frequencies 0.01–1 Hz and at 1 MHz with different saturating fluids (dry, argon, and water saturated) in two thermally cracked quartzite samples with ~2% total porosity. Measurements are made across a range of effective pressures (10–150 MPa), with the resulting very low permeabilities of the samples varying from 1–300 × 10−21 m2. Moduli across the 0.01–1 Hz band were typically independent of frequency. The shear moduli measured at sub‐Hz frequencies are unaffected by fluid saturation, as expected for the saturated isobaric (Gassmann) regime. In marked contrast, water saturation of the cracked rocks results in very large increases in the shear moduli measured at 1 MHz and low effective pressures, indicative of saturated isolated conditions. Thus, at an effective pressure of 20 MPa, the shear moduli for the two water‐saturated quartzites increase by 74% and 98% from 1 Hz to 1 MHz. The contrast in elastic moduli between dry and water‐saturated conditions is well represented by the theoretical model developed by Walsh and others. The observed dispersion highlights the need for care in seismological application of results obtained at MHz frequencies from laboratory ultrasonic measurements.

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Section: Characterization Of Rock Specimenscontrasting

confidence: 76%

Section: Discussionmentioning

confidence: 91%

Section: Characterization Of Rock Specimensmentioning

confidence: 99%

Section: Characterization Of Rock Specimensmentioning

confidence: 99%

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Shear Modulus Dispersion in Cracked and Fluid‐Saturated Quartzites: Experimental Observations and Modeling

2018

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“…The lower estimate of the Qaidam basin crustal temperature does not satisfy this limit. However, the decrease of Q β with an increase in temperature may accelerate above 400–500°C [ Lu and Jackson , 1996, 1998]; therefore the temperature of Qaidam basin could be less than 617°C, which suggests the presence of nearly a 100°C temperature change across the Kunlun Shan. As a comparison, Table 1 also lists the respective ranges of apparent Q Lg values at 1 Hz for the four terranes from Bao et al [2011], which does not remove the contribution of Q anisotropy or scattering.…”

Section: The Isotropic 1/qlg and Crustal Temperaturementioning

confidence: 99%

Azimuthal anisotropy of Lg attenuation in eastern Tibetan Plateau

Bao¹,

Sandvol²,

Chen³

et al. 2012

J. Geophys. Res.

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[1] The Q of seismic phase Lg is measured to approach the crustal Q b , which can be used to infer crustal rheology. A reverse two-station/event method is used to measure the interstation Q Lg , which theoretically eliminates effects from the source and site response. Strong azimuthal anisotropy of 1/Q Lg in northern Tibet is observed, which approximately correlates with the seismic velocity anisotropy observed using both surface waves and teleseismic S waves. Both the intrinsic and scattering attenuation contribute the isotropic Q, whereas the anisotropic Q may be associated with the fractures and faults in the crust. Strong 1/Q Lg is observed in the northwestern Songpan-Ganzi fold belt, where the high-Q directions correspond with the orientations of major strike-slip faults. Intrinsic and scattering Q values are estimated for different tectonic terranes in eastern Tibetan Plateau. The intrinsic Q values are approximately 500 in the northern Tibetan Plateau, which suggests a hot ($700 C) crust, consistent with low seismic velocity measurements. Our result suggests that the crust of northwestern Songpan-Ganzi fold belt may be hotter than that of the Qiangtang terrane, which may be related to the strain heating along the major strike slip fault zones that dominate the northernmost Tibet.

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A MATLAB toolbox and Excel workbook for calculating the densities, seismic wave speeds, and major element composition of minerals and rocks at pressure and temperature

Abers

Hacker

2016

Geochem Geophys Geosyst

141

186

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To interpret seismic images, rock seismic velocities need to be calculated at elevated pressure and temperature for arbitrary compositions. This technical report describes an algorithm, software, and data to make such calculations from the physical properties of minerals. It updates a previous compilation and Excel V R spreadsheet and includes new MATLAB V R tools for the calculations. The database of 60 mineral endmembers includes all parameters needed to estimate density and elastic moduli for many crustal and mantle rocks at conditions relevant to the upper few hundreds of kilometers of Earth. The behavior of a and b quartz is treated as a special case, owing to its unusual Poisson's ratio and thermal expansion that vary rapidly near the a-b transition. The MATLAB tools allow integration of these calculations into a variety of modeling and data analysis projects.

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Seismic-frequency Laboratory Measurements of Shear Mode Viscoelasticity in Crustal Rocks II: Thermally Stressed Quartzite and Granite

Cited by 6 publications

References 52 publications

Shear Modulus Dispersion in Cracked and Fluid‐Saturated Quartzites: Experimental Observations and Modeling

Shear Modulus Dispersion in Cracked and Fluid‐Saturated Quartzites: Experimental Observations and Modeling

Azimuthal anisotropy of Lg attenuation in eastern Tibetan Plateau

A MATLAB toolbox and Excel workbook for calculating the densities, seismic wave speeds, and major element composition of minerals and rocks at pressure and temperature

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