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The AAPG/Datapages Combined Publications Database

Houston Geological Society Bulletin


Houston Geological Society Bulletin, Volume 34, No. 9, May 1992. Pages 26-26.

Abstract: Detection of Naturally Occurring Micro-Fractures


Jamal Ass'Ad

The effects of oriented cracks in rocks (azimuthally anisotropic medium) on seismic shear-Previous HitwaveNext Hit propagation are characterized through scale-model seismic experiments utilizing disc-shaped inclusions in an isotropic epoxy matrix. Models built with rubber inclusions are analogous to fluid-filled cracks, microcracks, veins, and 'hard' inclusions. Shear-Previous HitwaveNext Hit velocities are calculated using the first arrivals, and velocities measured from data for two different models with velocity (S1) is almost constant and in agreement with the calculated velocity for the isotropic medium. However, the slow shear-Previous HitwaveNext Hit velocity (S2) decreases with increasing crack density up to a crack density of 10%, where a velocity increase is observed. This velocity increase at high crack density leads to a reduction in the velocity anisotropy (G). In contrast, for models with aluminum (stiff) inclusions, both fast (S1) and slow (S2) shear-Previous HitwaveNext Hit velocities are increased. Consequently, a consistent increase of velocity anisotropy (G) is observed. Shear-Previous HitwaveTop splitting in the case of rubber (soft) inclusions is more pronounced than its counterparts with aluminum (stiff) inclusions. Results of this study may be applied to detecting and differentiating between fluid-and mineral-filled cracks, veins, microcracks, and inclusions.

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