Comparison of static and dynamic measurements of compressibility of rocks

Simmons, Gene; Brace, W. F.

doi:10.1029/jz070i022p05649

Cited by 245 publications

(100 citation statements)

References 10 publications

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“…Reducing this estimate by a factor of 2 might approximately account for differences between the static and dynamic moduli at these low confining pressures [Simmons and Brace, 1965] and brings it closer to rough estimates of the static in situ modulus [Davis, 1976;Rubin and Pollard, 1987]. For v=0.25, AP then becomes about 2.5 MPa.…”

Section: Ap 25xl 0-4[g/(1-v)] (2)mentioning

confidence: 87%

Dike‐induced earthquakes: Theoretical considerations

Rubin¹,

Gillard²

1998

J. Geophys. Res.

148

114

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Abstract. Earthquakes of magnitude 1 and greater seem to be ubiquitous features of dike propagation, but their origin is not well understood. We examine the elastic stress field surrounding propagating fluid-filled cracks, with an emphasis on assessing the ambient stress required to produce earthquakes with linear dimensions of-100 m near dikes with linear dimensions of a few kilometers. An important feature of the solutions is the dike "tip cavity," a low-pressure region where magma cannot penetrate and where the stress field differs most from the classical near-tip stress field. Two regions are considered: near the dike tip but away from the tip cavity and near the tip cavity. The stress state most conducive to failure occurs near the tip cavity when the cavity pressure is maintained by influx of host rock pore fluids rather than by exsolution of magmatic volatiles. Even in this case, however, shear fracture of previously intact rock seems unlikely. Thus most dike-induced seismicity with a frequency content typical of "tectonic" earthquakes should be interpreted as resulting from slip along suitably aligned existing fractures. Production of magnitude 1 earthquakes appears to require either large ambient differential stresses or low ambient confining pressures; in the latter case, the effective normal stress on prospective faults may be low enough for slip to be aseismic. We conclude that the distribution of (recorded) dike-induced seismicity reflects the distribution of ambient stresses that are near to failure and does not necessarily reflect the extent of the dike. This result is consistent with recent images of the seismicity associated with the 1983 dike intrusion at Kilauea.

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Section: Ap 25xl 0-4[g/(1-v)] (2)mentioning

confidence: 87%

Dike‐induced earthquakes: Theoretical considerations

Rubin¹,

Gillard²

1998

J. Geophys. Res.

148

114

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“…This same Poisson's ratio to Young's modulus ratio for Westerly granite varies from 0.236 Mbar-1 [Fai, 1961) and 0.384 Mbar-1 [Knopo.ff. 1954) from dynamic measurements to 0.821, 0.961, and 1.549 Mbar-1 if we adopt the static compressibility data of Simmons and Brace [1965) and a Poisson's ratio of 0.271 [Knopoff. 1954; also consistent with the uniaxial compression E,JE, data by Brace et al, 1966). The spherical seat is used to reduce bending moments on the rock sample.…”

Section: Slit Diffraction Method: Theoretical Background and Experimementioning

confidence: 99%

Dilatancy and precursory bulging along incipient fracture zones in uniaxially compressed westerly granite

Liu¹,

Livanos²

1976

J. Geophys. Res.

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The existence of precursory bulge along an incipient fracture zone in a uniaxially compressed Westerly granite sample has been investigated by two optical methods. The first method is the method of slit diffraction. The cross section of a cylindrical rock sample is monitored by bringing two straightedges next to the rock sample to form two slits (each slit being formed between one straightedge and one side of the rock sample) and by illuminating alternately the two slits with a collimated laser beam. The FraunhoFer diffraction pattern is recorded on film in the direction perpendicular to the straightedge and can be interpreted as the absolute value squared of the one-dimensional spatial Fourier transform of the slit under certain conditions, thereby providing a simple method of magnification of the rock surface geometry. The conditions under which the Fraunhofer diffraction pattern can be interpreted as the absolute value squared of a one-dimensional Fourier transform are related to the radius of the rock sample, width of the slit, position of the recording film plane, and nature of deformation of the rock surface and are presented in this paper. The films are digitized by a microdensitometer. The data are analyzed by digital filtering and interpolation techniques to give a strain resolution of 10-•. During a test with the slit diffraction method, strain inhomogeneities in terms of local bulges indicative of incipient failure zones were found to develop at -92% of the uniaxial compressive strength, and their propagation is traced at 2.66-s intervals until failure. Local strains in the incipient failure zones are of the order of 10-• before failure takes place. Because of the large amplitude of the strain inhomogeneity prior to failure recorded by the slit diffraction method, we then tried the faster method of recording without magnification by a motion picture camera. In the second test a precursory bulge in the middle of the sample first appeared at -3.75 s prior to failure at a load of >99.7% of the uniaxial compressive strength. The bulge developed rapidly in successive frames until eventually a failure plane passed through this sharp bulge. The results from both tests demonstrate the formation of a concentrated weak zone as a result of the interaction and coalescence among the microcracks in the final stage of the test, which then develop into fracture zones. The bulging is the result of accentuated deformation in the weak zone because of its reduced deformation moduli. It is considered that the local bulge and orientation of the fracture zones in the first test were controlled by the stress concentration at the sample-load block interface, whereas those in the second test were controlled mainly by the inhomogeneity in the material properties within the sample. The precursor times of both tests do not fit into the empirical relationship between precursor time and fault dimension as derived from earthquakes and mine rock bursts. The precursor times of these tests are too long by 3 orders of magnitude in compa...

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“…For many nonporous rocks, the effect is small (Simmons and Brace, 1965;Stowe and Ainsworth, 1972;Green and Perkins, 1972). However, in porous media strain-rate effects are often quite large.…”

Section: I~trodlctionmentioning

confidence: 99%

Measurements of the longitudinal modulus of Pierre clay shale at varying strain rates

1978

International Journal of Rock Mechanics and Mining Sciences &am

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Comparison of static and dynamic measurements of compressibility of rocks

Cited by 245 publications

References 10 publications

Dike‐induced earthquakes: Theoretical considerations

Dike‐induced earthquakes: Theoretical considerations

Dilatancy and precursory bulging along incipient fracture zones in uniaxially compressed westerly granite

Measurements of the longitudinal modulus of Pierre clay shale at varying strain rates

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