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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Detection of Naturally Occurring
Micro-Fractures
By
The effects of oriented cracks in rocks (azimuthally
anisotropic medium) on seismic shear-wave 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-wave 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-wave
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-wave velocities are increased.
Consequently, a consistent increase of
velocity
anisotropy
(G) is observed. Shear-wave 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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