A method is reported for the production of synthetic porous sandstones containing cracks of known dimensions and geometry with respect to the matrix. A synthetic sandstone was manufactured from Sand cemented with an epoxy glue. The cracks of known geometry were introduced into the material in the manufacturing stage, by emplacing thin metallic discs in the Sand-epoxy matrix. These discs were chemically leached out of the consolidated porous sandstone. Acoustic anisotropy. and shear-wave splitting were observed in the synthetic sandstones. For the dry sample the observed angular dependence of the P-and S-wave velocities (at 100 kHz) compares well, qualitatively, with the theoretical models of Hudson and of Thomsen. Quantitatively, however, the experimental data fits Hudson's model better. For the case of a saturated sample the experimental results are in excellent agreement with Thomsen's model. Hudson's model, on the other hand, predicts a different angular dependence for P-waves. This demonstrates that the concept of fluid transfer between cracks and the ambient porosity can be a significant process. The results reported here are from the first successful experiment in which the theoretical models were tested on a porous material containing a known crack geometry .

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Aliasing has been a problem in both formal verification and practical programming for a number of years. To the formalist, it can be annoyingly difficult to prove the simple Hoare formula {x = true} y := false {x = true}. If x and y refer to the same boolean variable, i.e., x and y are aliased , then the formula will not be valid, and proving that aliasing cannot occur is not always straightforward. To the practicing programmer, aliases can result in mysterious bugs as variables change their values seemingly on their own. A classic example is the matrix multiply routine mult(left, right, result) which puts the product of its first two parameters into the third. This works perfectly well until the day some unsuspecting programmer writes the very reasonable statement mult(a, b, a). If the implementor of the routine did not consider the possibility that an argument may be aliased with the result, disaster is inevitable.

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A better understanding of seismic dispersion and attenuation of acoustic waves in rocks is important for quantitative interpretation of seismic data, as well as for relating seismic data, sonic-log data, and ultrasonic laboratory data. In the present work, a new laboratory setup is described, allowing for combined measurements of quasi-static deformations of rocks under triaxial stress, ultrasonic velocities, and dynamic elastic stiffness (Young's modulus and Poisson's ratio) at seismic frequencies.The setup has been used mainly for the study of shales. For such rocks, it is crucial that the saturation of the samples is preserved, which requires fast sample mounting. Design of our setup together with a technique that was developed for rapid mounting of strain gages onto the sample and subsequent sealing of the sample allows for sample preservation, which is of particular importance for shales.The performance of the new experimental setup and sample-mounting procedure is demonstrated with test materials (Aluminum and PEEK) as well as two different shale types (Mancos shale and Pierre shale). Furthermore, experimental results are presented that demonstrate the capability of measuring the impact of saturation, stress and stress-path on seismic dispersion. For the tests with Mancos and Pierre shale, large dispersion (up to 50% in Young's modulus normal to bedding) was observed. Increased water saturation of Mancos shale results in strong softening of the rock at seismic frequencies, while hardening is observed at ultrasonic frequencies due to an increase in dispersion, counteracting the rock softening. Poisson's ratio of Mancos shale strongly increases with level of saturation but appears to be nearly frequency independent. We have found that the different types of shale exhibit different stress sensitivities during hydrostatic loading, and also that the stress sensitivity is different at seismic and ultrasonic frequencies.