Shear waves revealed: Extensive‐dilatancy anisotropy confirmed

Crampin, Stuart; Bush, I.

doi:10.1190/1.1893033

Cited by 12 publications

(5 citation statements)

References 5 publications

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“…Following the procedure first outlined = el, c g i , 2~~~~ = zqi and 2~~~~ by Helbig and Schoenberg (1987) for general anisotropic layers, define the following vectors …”

Section: -mentioning

confidence: 99%

“…A concise way to pose the problem of finding the effective moduli, even when the constituent layers are anisotropic, is through a matrix formulation which distinguishes components that are constant over many layers from the other components which can vary from layer to layer. Following the procedure first outlined by Helbig and Schoenberg (1987) for general anisotropic layers, define the following vectors ) and solving this for E,i and substituting into (3a) yields n Now let the thickness-weighted average over all the constituent layers, 1 hi(.i), be denoted as ( . ).…”

Section: -mentioning

confidence: 99%

“…It is now clear that there are many regions of the subsurface (some say everywhere) showing azimuthal velocity anisotropy and this has been attributed to the presence of aligned vertical microcracks that arise because of tectonic stresses (see e.g. Crampin 1985;Crampin and Atkinson 1985;Willis, Rethford and Bielanski 1986;Crampin and Bush 1986). That this Crampin model is the actual mechanism causing the azimuthal velocity anisotropy is difficult to say as drilling and coring in such a region distort the stress field locally and perhaps distort and close the cracks that existed in the undeformed rock.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

ELASTIC WAVE PROPAGATION IN MEDIA WITH PARALLEL FRACTURES AND ALIGNED CRACKS¹

Schoenberg

Douma

1988

Geophysical Prospecting

490

245

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SCHOENBERG, M. and DOUMA, J. 1988. Elastic wave propagation in media with parallel fractures and aligned cracks. Geophysical Prospecting 36,571-590.A model of parallel slip interfaces simulates the behaviour of a fracture system composed of large, closely spaced, aligned joints. The model admits any fracture system anisotropy : triclinic (the most general), monoclinic, orthorhombic or transversely isotropic, and this is specified by the form of the 3 x 3 fracture system compliance matrix. The fracture system may be embedded in an anisotropic elastic background with no restrictions on the type of anisotropy. To compute the long wavelength equivalent moduli of the fractured medium requires at most the inversion of two 3 x 3 matrices. When the fractures are assumed on average to have rotational symmetry (transversely isotropic fracture system behaviour) and the background is assumed isotropic, the resulting equivalent medium is transversely isotropic and the effect of the additional compliance of the fracture system may be specified by two parameters (in addition to the two isotropic parameters of the isotropic background). Dilute systems of flat aligned microcracks in an isotropic background yield an equivalent medium of the same form as that of the isotropic medium with large joints, i.e. there are two additional parameters due to the presence of the microcracks which play roles in the stressstrain relations of the equivalent medium identical to those played by the parameters due to the presence of large joints. Thus, knowledge of the total of four parameters describing the anisotropy of such a fractured medium tells nothing of the size or concentration of the aligned fractures but does contain information as to the overall excess compliance due to the fracture system and its orientation. As the aligned microcracks, which were assumed to be ellipsoidal, with very small aspect ratio are allowed to become non-flat, i.e. have a growing aspect ratio, the moduli of the equivalent medium begin to diverge from the standard form of the moduli for flat cracks. The divergence is faster for higher crack densities but only becomes significant for microcracks of aspect ratios approaching 0.3.

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“…Following the procedure first outlined = el, c g i , 2~~~~ = zqi and 2~~~~ by Helbig and Schoenberg (1987) for general anisotropic layers, define the following vectors …”

Section: -mentioning

confidence: 99%

Section: -mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

ELASTIC WAVE PROPAGATION IN MEDIA WITH PARALLEL FRACTURES AND ALIGNED CRACKS¹

Schoenberg

Douma

1988

Geophysical Prospecting

490

245

View full text Add to dashboard Cite

show abstract

“…This difference was attributed to the systematic presence in the sandstone samples of a vertical set of microcracks causing a minimum P-wave velocity to be found along the strike of the bedding, as opposed to finer grained lithologies where APV was dominated by the effect of the bedding. Pervasive sets of vertical microcracks are considered to be ubiquitous in the crust (Simmons and Richter, 1976) and are held responsible by some authors for shear-wave azimuthal anisotropy (Crampin, 1986(Crampin, , 1987Willis et al, 1986;Crampin and Peacock, 2008). Intra-and inter-granular microcracks typically form under differential stress at the nucleation sites (Zhang et al, 1990;Wong and Wu, 1995) and propagate at various velocities depending on stress conditions and water vapor saturation (Wiederhorn, 1967;Atkinson, 1984).…”

Section: Introductionmentioning

confidence: 99%

Magnetic inference of in situ open microcracks in sandstone samples from the Taiwan Chelungpu Fault Drilling Project (TCDP)

Humbert

Robion

Louis

et al. 2012

Journal of Asian Earth Sciences

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“…As discussed, simply recording data in arbitrary X and Y receivers of a survey coordinate system defined by the acquisition geometry is not necessarily optimum to the analysis and interpretation of shear waves polarizations for analysis of azimuthal anisotropy (Alford, 1986;Crampin, 1986). An early step in the analysis procedure has often been used to rotate the observed S-wave reflection polarizations to source to receiver oriented radial and transverse coordinates (Figure 56), where radial and transverse components are defined by the direction or azimuth between the source and receiver locations.…”

Section: Rotating Survey Coordinatesmentioning

confidence: 99%