The permeability of Westerly granite was measured as a function of effective pressure to 4 kb. A transient method was used, in which the decay of a small incremental change of pressure was observed; decay characteristics, when combined with dimensions of the sample and compressibility and viscosity of the fluid (water or argon) yielded permeability, k. k of the granite ranged from 350 nd (nanodarcy = 10−17 cm2) at 100‐bar pressure to 4 nd at 4000 bars. Based on linear decay characteristics, Darcy's law apparently held even at this lowest value. Both k and electrical resistivity, ρs, of Westerly granite vary markedly with pressure, and the two are closely related by k = Cρs−1.5±0.1, where C is a constant. With this relationship, an extrapolated value of k at 10‐kb pressure would be about 0.5 nd. This value is roughly equivalent to flow rates involved in solute diffusion but is still a great deal more rapid than volume diffusion. Measured permeability and porosity enable hydraulic radius and, hence, the shape of pore spaces in the granite to be estimated. The shapes (flat slits at low pressure, equidimensional pores at high pressure) are consistent with those deduced from elastic characteristics of the rock. From the strong dependence of k on effective pressure, rocks subject to high pore pressure will probably be relatively permeable.

Compressibility of porous material is greater than that of solid material of the same composition, and the difference is shown to be equal to rate of change of porosity with pressure, for any pore shape or concentration. Expressions for compressibility are given for two special cases for material of low pore concentration: for spherical pores and for narrow cracks. Comparison of the two cases shows that a crack increases compressibility nearly as much as a spherical pore of the same diameter as the length of the crack, although porosity in these two cases differs enormously. For material in which all porosity occurs as narrow cracks, it is shown that porosity can, in certain cases, be determined quite precisely from compressibility measurements.

We reanalyze the flow model proposed by Wyllie and Rose (1950) in which the complicated flow network through the pore phase of rock is replaced by a single representative conduit. Although the model is a very simple representation of the complicated pore phase in rock, we find that it provides an adequate simulation of how the transport properties vary with external pressure. Expressions derived for fluid permeability k and formation factor F are combined to give an expression for the mean hydraulic radius of the pore phase. Using this expression, we show that the exponent r in the empirical relationship k oc F-' must fall in the range 1 < r < 3. Also, we use the expression for hydraulic radius to estimate the crack area per unit volume and the standard deviation of the height of the asperities on the microcrack surfaces for two granites. The values are in reasonable agreement with other estimates.

Uniaxial elastic compression of rocks is characterized by nonlinear stress-strain behavior and hysteresis. Both effects, which are due to cracks, are analyzed here. An isotropic solid filled with a low concentration of planar elliptical cracks is used as a model. Young's modulus for an elastic solid containing cracks is less than that for an identical solid without cracks. The cracks close under increasing compressire stress, causing an increase in modulus.However, even when applied stress is sufi%ient to close all cracks, the modulus may still not be equal to that of solid material, since frictional sliding at crack faces can occur. It is shown that cracks which have slid do not immediately slide in the opposite sense when the load is lowered; thus Young's modulus for the material without cracks can be found by measuring the initial slope of the unloading part of the stress-strain curve of a cracked material.

A model of partially melted rock is analyzed in which melt occurs as thin films along grain boundaries. For analysis, the liquid phase is assumed to be a dispersion of randomly oriented ellipsoidal inclusions with minor axes much smaller than major axes. Expressions are derived for complex bulk modulus and rigidity. Rigidity and attenuation in pure shear are found to depend on the number of sites at which melting has occurred rather than to depend only on the concentration of melt, in agreement with published observations. On the other hand, response in pure dilatation depends on concentration alone, with the result that attenuation in pure dilatation is low and bulk modulus is approximately equal to that for unmelted material.

The seismic velocity and attenuation were measured for P, S⊥, and S∥ waves traveling through a sample of Westerley Granite as it was deformed to failure under a confining pressure of 500 bars. All waves traveled in a direction normal to the axis of maximum compression, with S∥ polarized parallel to the axis and S⊥ polarized normal to it. By the time failure occurred, all seismic velocities had decreased by 12–30%. Amplitudes of the S⊥ and P waves decreased by approximately 30%. A remarkable result of the experiment is that the amplitude of the S∥, wave increased throughout the experiment until near failure. The amplitude at 90% failure strength was more than twice the value under hydrostatic pressure alone. These results are explained by analyzing how elastic moduli and energy dissipation due to frictional sliding at cracks are affected by anisotropic crack distribution developed in the sample as axial stress is applied.

Retinal MAs can be classified in vivo into six different morphologic types, according to the geometry of their two-dimensional (2D) en face view. Adaptive optics scanning light ophthalmoscope fluorescein angiography imaging of MAs offers the possibility of studying microvascular change on a histologic scale, which may help our understanding of disease progression and treatment response.

The total attenuation in rock is probably due to a number of sources of dissipation. The mechanism proposed here as one source of attenuation is based on the frictional dissipation as crack surfaces in contact slide relative to one another during passage of a seismic wave. The attenuation due to friction at cracks is derived for dilatation and shear waves under the assumption that the cracks may be approximated as elliptical slits in plane strain. The results cannot be evaluated on an absolute basis; however, the ratio Qα/Qβ of the quality factor for longitudinal waves to that for transverse waves predicted by the theory agrees reasonably well with published values (all of which equal approximately 0.5) found in laboratory experiments on granite and limestone.