Laboratory measurements of elastic anisotropy parameters for the exposed crustal rocks from the Hidaka Metamorphic Belt, Central Hokkaido, Japan

Takanashi, Mamoru; Nishizawa, O.; Kanagawa, Kyuichi; Yasunaga, Kazuaki

doi:10.1046/j.1365-246x.2001.00332.x

Cited by 14 publications

(44 citation statements)

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“…One of the important factors controlling the closure pressure of a dry crack is its geometry. Thin cracks with large aspect ratios generally close at low pressures (≤100 MPa [ Walsh , 1965; Takanashi et al , 2001]), whereas spherical pores can remain open at pressures > 200 MPa [ Nur and Simmons , 1969]. Hysteresis is observed for velocities when P C is reduced to room pressure, due to some porous spaces and cracks that do not reopen.…”

Section: Sample Preparation and Methodsmentioning

confidence: 99%

Elastic properties of anisotropic synthetic calcite‐muscovite aggregates

Almqvist¹,

Burlini²,

Mainprice³

et al. 2010

J. Geophys. Res.

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[1] A set of synthetic aggregates, containing mixtures of calcite and muscovite, were compacted with varying uniaxial loads ranging from 20 MPa up to 400 MPa. Their elastic properties have been measured using compressional and shear waves in confining hydrostatic pressures up to 475 MPa. Measured seismic velocities are shown to depend on 1) the ratio of calcite to muscovite, 2) the uniaxial load used during sample manufacturing, and 3) the porosity amount prior to velocity measurements. The matrix framework may also affect the seismic velocities, but this effect is not easily quantifiable. In general, measured seismic velocities decrease with increasing muscovite content and porosity. Elastic properties have been calculated based on texture measurements, which were obtained by neutron diffraction. The calculated velocities are based on the calcite and muscovite single crystal elastic tensors, their orientation distribution functions, and their modal fractions. A large discrepancy is apparent between calculated and measured velocities, where the former always overestimate the actual velocities. Shear waves display less of a difference between calculated and measured values, than do compressional waves, indicating that waves propagating by shearing are less affected by sample porosity and matrix framework. A better agreement between measured and calculated seismic velocities arises when the initial porosity is taken into account, using a differential effective medium model. Seismic anisotropy is evident from both measured and calculated velocities, and is low for samples containing pure calcite, but becomes prominent as the muscovite concentration increases. The intensity of anisotropy further depends on the uniaxial load used during sample compaction and the initial porosity.

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Section: Sample Preparation and Methodsmentioning

confidence: 99%

Elastic properties of anisotropic synthetic calcite‐muscovite aggregates

Almqvist¹,

Burlini²,

Mainprice³

et al. 2010

J. Geophys. Res.

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“…In recent years, many workers (e.g., Takanashi et al 2001) have used "ε -δγ" parameterizations that allow approximate calculation of the variation in velocity with direction using simpler trigonometric formulas. The original formulas may be found in Thomsen (1986) and Tsvankin (1997) for transversely isotropic and orthorhombic materials, respectively.…”

Section: Elasticity Of An Anisotropic Medium -A Reviewmentioning

confidence: 99%

“…More recently, Takanashi et al (2001) reported results on P-and S-wave velocity measurements for several amphibolites, a biotite gneiss and a biotite schist from the Hidaka Metamorphic Belt, Japan. The observed pattern of seismic anisotropy in this case strongly correlates with the LPO of rock-forming hornblende and biotite.…”

Section: Introductionmentioning

confidence: 99%

Flin Flon Belt seismic anisotropy: elastic symmetry, heterogeneity, and shear-wave splitting

Cholach¹,

Molyneux²,

Schmitt³

2005

Can. J. Earth Sci.

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Laboratory measurements of compressional- and shear-wave velocities, and shear-wave splitting have been carried out on a set of upper greenschist lower amphibolite facies of metasediments and metavolcanics and plutonic rocks from two ductile shear zones in the Flin Flon Belt (FFB) of the Trans-Hudson Orogen (THO). Selected metamorphic rocks vary in composition from felsic to mafic. Test sites with outcrops of sheared metamorphic rocks were correlated with a series of inclined seismic reflectors possibly extending from the midcrust and intersecting a well-mapped shear zone at the surface. Determination of the lithological and physical properties of highly deformed metamorphic rocks is essential for proper interpretation of the nature of observed seismic reflectors. To investigate the anisotropic properties of the rocks, compressional velocity was measured at confining pressure up to 300 MPa in three mutually orthogonal directions aligned with respect to visible textural features. In addition, on selected samples, shear-wave velocity was measured at two orthogonal polarizations for each of three propagation directions to determine shear-wave splitting. The seismic heterogeneity of hand specimens was also investigated by measuring P- and S-wave velocities on several cores cut in the same direction. Observed compressional-wave anisotropy varied from quasi-isotropic to 24%. Maximum observed shear-wave splitting reaches a value of 0.77 km/s at confining pressure of 300 MPa. The pressure invariance of observed P-wave anisotropy and shear-wave splitting indicates that intrinsic anisotropy due to the lattice-preferred orientation (LPO) of highly anisotropic minerals, such as mica and hornblende, is mainly responsible for the measured seismic anisotropy.

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“…in which values are based on the specification of orthotropic biotite schist analysed by Takanashi et al (2001). The value of C 12 is unknown, but we do not needed it for our purposes.…”

Section: A P P E N D I X B : E X a M P L E S O F E L A S T I C I T Y mentioning

confidence: 99%

Orthotropic anisotropy: on contributions of elasticity parameters to a difference in quasi‐P‐wave‐squared velocities resulted from propagation in two orthogonal symmetry planes

Adamus

2020

Geophysical Prospecting

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We investigate the dependence of quasi P‐wave phase velocity propagating in orthotropic media on particular elasticity parameters. Specifically, due to mathematical facilitation, we consider the squared‐velocity difference, s2, resulted from propagation in two mutually perpendicular symmetry planes. In the context of the effective medium theory, s2 may be viewed as a parameter evaluating the influence of cracks – embedded in the background medium – parallel to one or both aforementioned planes. Our investigation is both theoretical and numerical. Based on Christoffel's equations, we propose two accurate approximations of s2. Due to them, we interpret the aforementioned squared‐velocity difference as being twice more dependent on C55−C44, than on C13−C23. To describe the magnitude of the dependence, we consider the proportions between the partial derivatives of s2. Further, it occurs that s2 is influenced by the ratio of vertically propagating quasi P‐wave to vertically propagating quasi S‐wave. Anomalously high s2 might be caused by the low P/S ratio, which in turn can be an indicator of the presence of gas in natural fractures or aligned porosity. Also, we carry out numerical sensitivity study, according to which s2 is approximately twice more dependent on C55 than on C13, twice more sensitive to C44 than to C23, and equally dependent on −C33 as on C13+C23. The dependence on C11 and C22 can be neglected, especially for small phase angles. We verify the approximations and perform the sensitivity study, using eight examples of the elasticity tensors.

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Laboratory measurements of elastic anisotropy parameters for the exposed crustal rocks from the Hidaka Metamorphic Belt, Central Hokkaido, Japan

Cited by 14 publications

References 0 publications

Elastic properties of anisotropic synthetic calcite‐muscovite aggregates

Elastic properties of anisotropic synthetic calcite‐muscovite aggregates

Flin Flon Belt seismic anisotropy: elastic symmetry, heterogeneity, and shear-wave splitting

Orthotropic anisotropy: on contributions of elasticity parameters to a difference in quasi‐P‐wave‐squared velocities resulted from propagation in two orthogonal symmetry planes

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