Gene Simmons

The effect of saturation on velocity in low porosity rocks

Abstract V p and V s are often significantly lower near atmospheric pressure than at pressures of a few kilobars for dry rocks with porosity in the form of cracks. When such cracks are filled with water, however, this lowering of velocity is significantly diminished for compressional waves. In contrast, V s is unaffected by the presence of fluid; low velocity persists at low pressure. The shape of the pores in typical crystalline rocks plays an important role: increase in V p due to saturation of pores occurs when the pores are in the form of cracks but not when they are in the form of round holes. As differences in V p of dry and saturated rock at low pressure may approach 50 per cent, the degree of saturation of rocks must be taken into account in many engineering and shallow seismic applications.

Thermal expansion behavior of igneous rocks

New experimental data on the thermal expansion of several igneous rocks over the range 25–550°C show that the observed thermal expansion is a function of crack porosity, heating rate, and previous maximum temperature as well as mineralogical composition and preferred crystal orientation. For heating rates if≤2°C/min and a maximum temperature ≤250°C; expansion curves are reproducible, may show a small hysteresis but no permanent strain, and the coefficient of thermal expansion (α) is approximately that calculated from the single crystal values of the constituent minerals. For highly cracked rocks α is significantly less than the calculated value. For heating rates >2°C/min or T > 35°C, new cracks and hence permanent strain are produced in the sample and α is systematically decreased. Recycling to the same temperature produces additional cracks until a steady state is reached after 2–5 cycles.

Thermal conductivity of rock-forming minerals☆

Abstract New values of the thermal conductivity, K of 119 rock-forming minerals reveal the following empirical relationships: (1) K is a linear function of density for constant mean atomic weight (similar to Birchs law for the velocity of compressional waves); (2) the K of silicates is controlled by the structure of the silicon-oxygen network; (3) within a group of minerals of similar crystal structure and bonding, K decreases as the mean atomic weight increases; (4) for a series of minerals which form a binary solid solution, K has a minimum at an intermediate composition; and (5) the K of silicates is related linearly to elastic wave velocities.

The origin of small cracks in igneous rocks

Abstract The difference in compressional velocities at pressures of 1 atm and 10 kb, a sensitive indicator of microcrack porosity, is closely related to the presence of quartz in many igneous rock samples. The origin of such cracks can be attributed to the relatively high values of thermal expansion and compressibility of quartz. Only few cracks are introduced by drilling in stressed rocks.

Pressure and Temperature Dependences of the Isotropic Elastic Moduli of Polycrystalline Alumina

The isotropic elastic moduli of polycrystalline alumina have been determined as a function of hydrostatic pressure up to 10 kbar and also as a function of temperature over the range 4.2° to about 1300°K. The pressure dependence of the elastic moduli is linear over this pressure range. The low‐temperature limit of the elastic Debye temperature, 1044 (±3) °K, compares very well with thermal Debye temperature. Values of various pressure derivatives evaluated at 298°K are as follows: Pressure derivatives   dL/dp   dG/dp   dB/dp(∂Ms/∂p)T6.57 (6.58)1.79 (1.73)4.19 (4.27)(∂MT/∂p)T6.621.794.23(∂Ms/∂p)s6.521.734.16 The quantities in the parentheses are averaged values calculated from the single‐crystal second‐order elastic constants and their first pressure derivatives. The experimental data are interpreted with respect to (a) the polycrystalline data calculated from the corresponding single‐crystal data, (b) the temperature dependence of the isotropic elastic moduli, (c) the acoustic Gruneisen parameters and thei...

The ratio V p /V s as a discriminant of composition for siliceous limestones

The ratio of the velocity of compressional waves, Vp, to the velocity of shear waves, Vs, is an important parameter for interpreting geophysical field data. Recent studies have emphasized the role played by pore geometry in controlling Vp/Vs in homogeneous rocks. We measured the carbonate content of a set of siliceous limestones of varying proportions of carbonate and silica and observed the pore structures of these samples using a scanning electron microscope. The range of Vp/Vs at 1.0 kbar is from 1.6 to 2.0. The behavior of Vp/Vs of individual samples during increasing confining pressure is consistent with crack‐closure theory. However, the value of Vp/Vs within the sample set as a whole is dominated by its carbonate content. Variations in Vp/Vs due to total porosity and pore geometry are around 0.1, whereas the change due to composition is 0.4. Values of pore aspect ratios gained from comparison of the velocity‐porosity‐composition data with theory are in good agreement with the electron microscope ob...

Heat flow studies: Constraints on the distribution of uranium, thorium and potassium in the continental crust

Abstract To study the amount of heat generated by radioactive decay in the continental crust, the usual practice in the literature is to fit to the heat flow and radioactivity data a relationship of the form: Q = Q r + D · A where Q and A are the observed heat flow and radiogenic heat production. Q r is the “reduced” heat flow and D is a depth scale. This procedure implicitly assumes that uranium, thorium and potassium have identical distributions in the crust. We suggest that significant information may be lost as the three radioelements may in fact be affected by processes operating over different depths. Data published for four heat flow provinces throughout the world are used to estimate the distributions of uranium, thorium and potassium in the continental crust. These distributions are characterized by a depth scales defined as follows: D i =∫0h C i (z)C i (0)dz where h is the thickness of the layer containing the bulk of radioactivity and C i (z) the concentration of element i at depth z . Three depth scales are computed from a least-squares fit to the following relationship: Q = Q r + D U · A U + D T · A T + D K · A T where Q is the observed heat flow and Q r some constant (a reduced heat flow). A i is the heat generation rate due to the radioactive decay of element i , and D i is the corresponding depth scale. The analysis suggests that the three distributions are different and that they have the same basic features in the four provinces considered. The depth scale for potassium is large in granitic areas, that for thorium is small and that for uranium lies between the other two. We propose a simple model according to which each radioelement essentially provides a record for one process. Potassium gives a depth scale for the primary differentiation of the crust. Thorium gives the depth scale of magmatic or metamorphic fluid circulation. Finally, the uranium distribution reflects the late effects of alteration due to meteoric water. We show that the heat flow and radioactivity data are compatible with this model. Our analysis and numerical results are supported by data from deep boreholes and by geochemical evidence, such as detailed investigations of plutonic series and studies of U-Th-Pb systematics.

The effect of viscosity of a fluid phase on velocity in low porosity rocks

Abstract The effective shear modulus of a low porosity rock depends strongly on the viscosity of any fluid phase present in the microcracks. The bulk modulus is essentially independent. These results applied to the earth show remarkable (or perhaps fortuitous) agreement between the laboratory data and the facts known about the velocity zone in the upper mantle.

The effect of cracks on the thermal expansion of rocks

Abstract Thermal expansion during the first heating cycle at atmospheric pressure was measured in several directions in seven igneous rocks between 25° and 400°C at slow heating rates. The coefficient of thermal expansion measured under these conditions increases more rapidly as temperature is increased than the average thermal expansion coefficient of the constituent minerals. The “extra” expansion is attributed to the formation of cracks by differential expansion of mineral grains. The presence of such cracks in the rocks during the cooling part of the cycle and during any subsequent heating and cooling cycles will result in a substantial decrease in the coefficient of thermal expansion as compared to that measured during the first heating cycles. The effect of cracks initially present in a rock was studied by measuring the full tensor of the coefficient of thermal expansion on two rocks with anisotropic crack distributions. In these two rocks the coefficient of thermal expansion is least in the direction perpendicular to the plane of greatest crack concentration. The implication of our data is that thermal expansion depends greatly on the fracture state of the rock. Both the fractures in the rock and the boundary conditions on the rock are significant for the interpretation of thermal expansion measurements and for their application to other problems.

Granites: Relation of Properties in situ to Laboratory Measurements

The velocity of compressional waves and electrical resistivity in granite in situ measured in two 3-kilometer boreholes exhibits very little variation with depth, in contrast with the variation predicted from laboratory measurements on dry samples. These observations can be explained either by the absence of small open cracks in the rocks in situ or by the effects of complete saturation with water. The seismic velocities of many granites at shallow depths in the earths crust may be significantly larger than was previously believed. Other properties are also affected; correction for the effect of cracks on thermal conductivity raises the average heat flow in shield areas by as much as 20 percent.