228A of an explosive charge. In some areas, permanent strength and stiffness loss was observed. Results are discussed and possible explanations put forward.
934168 Engineering equivalent linear analysis of soils in the frequency domain Lin, J S Eartlul Engng Struct Dynam 1122, NI, Jan 1993, P75-88 An engineering equivalent linear method, widely used in soil dynamics to handle soil nonlinearity, has been tested in the frequency domain. The baseline for evaluation is a stochastic linearization analysis by Wen and Baber. Predicted stationary responses of single degree of freedom nonlinear systems are compared. The engineering equivalent linear analysis underpredicts rms displacements, but gives good estimates of rms acceleration responses. Frequency response functions of acceleration from both approaches agree well.
934169 Acoustic attenuation in oceanic gabbro Goldberg, D; Badri, M; Wepfer, W Geophys J Vlll, N2, Nov 1992, P193-202 P wave velocity and attenuation have been measured on nearly 0.5km of Ocean Layer 3 core recovered from ODP site 735 in the Indian Ocean. Shipboard acoustic measurements were made at 400kHz and room temperature and pressure on 117 water-saturated mini-core samples. Further tests were carried out an elevated effective pressure of 10-500MPa. Pressure dependence of acoustic properties was minimal. Close examination of cores indicates that it may be possible to estimate the relative degree of tectonism or alteration at depth in the crust on the basis of seismic measurements.
934170 Physical model study of microcrack-indueed anisotropy Ass'ad, J M; Tatham, R H; McDonald, J A Geophysics V57, NI2, Dec 1992, P1562-1570 Physical models of epoxy resin containing penny shaped rubber inclusions have been used to test the theory of Hudson (1981) on propagation of seismic shear waves in a material containing cracks. The limit of crack density for which this theory holds is examined, and effects of microcrack orientation and crack density on shear wave propagation are analysed. All the experiments were carried out with propagation parallel to crack orientation.
934171 Influence of fluids on grain contact stiffness and frame moduli in sedimentary rocks Tutuncu, A N; Sharma, M M Geophysics V57, N12, Dec 1992, P1571-1582 A new model is presented for the contact deformation problem in sedimentary rocks, incorporating effects of surface forces -electrostatic repulsion, Born, structural, and Van der Waals forces. Expressions are derived for velocity and attenuation of P and S waves as functions of frequency, net intergranular stress, fluid type, and fluid saturation. Theoretical values are in good agreement with laboratory measurements on glass beads and a range of sandstones.
934172 Hollow glass microspheres inhibit blast-induced liquefaction Charlie, W A; Johnson, W F; Doehring, D O Geotech Test J V15, N4, Dec 1992, P362-370 The presence of small amounts of gas is known to reduce P wave velocity and liquefaction potential of soils. The potential for using hollow microspheres (collapse strength about
1700kPa) to inhibit dynamic liquefaction has been examined in the laboratory. Mixtures of Monterey 0/30 sand, microspheres, and water were subject to a sub-millisecond compressive stress pulse of about 2300kPa. Results are presented. Analysis suggests that the microspheres will act as a passive measure to inhibit blast-induced liquefaction and reduce peak blast-induced stress in saturated soils.
934173 Application of seismic methods for dynamic characterization of soils in earthquake engineering Jongmans, D Int Assoc Engng Geol Bull N46, Oct 1992, P63-69 A wide range of field methods is available to determine the wave velocities and quality factors of soil required for site effect evaluation. S wave velocity, from which in situ shear modulus can be calculated, is an important parameter. Surface wave inversion is a promising technique for measurement of depth variation of Vs, since it does not require boreholes and surface waves can be recorded during standard refraction surveys. Determination of attenuation (quality factor) still presents problems. Spectral ratio and rise time methods for Q are illustrated.
934174 Wave propagation in random anisotropic media Jannaud, L R; Adler, P M; Jacquin, C G J Geophys Res V97, NBll, Oct 1992, P15277-15289 A method is presented to determine the characteristic lengths of anisotropic two dimensional media on the basis of linear theory of Aki and Chouet (1975) and Sato (1982). Two dimensional media with bivariable Gaussian functions are generated using bivariable Gaussian filters in the spatial spectral domain. Wave propagation is simulated by the finite difference method. The correlation lengths are extracted from the codas. For Gaussian correlation functions and weak velocity fluctuations, the geometrical anisotropy of velocity distribution does not induce any propagation anisotropy. The spectral power of codas for Boolean media is also analysed.
934175 Sonic log data helps determine formation strength Stein, N Oil Gas J V90, N52, Dec 1992, P96-99 A set of equations is presented to provide improved estimations of static strength of rocks from values of their acoustic wave velocity. Data for calibration were obtained from triaxial tests on 5 limestones with different porosities, at a range of confining pressures. Advice is given on precautions required when applying this method to acoustic log data.
934176 Scattering of elastic waves by a fracture zone containing randomly distributed cracks Kawahara, J; Yamashita, T Pure Appl Geophys V139, N1, 1992, P121-144 Scattering of P, SV, and SH waves by an array of aligned cracks of identical length randomly distributed in a zone of finite width is examined. Effects of geometrical properties of crack distribution and frictional properties of the crack surfaces (wet or dry) on attenuation and dispersion of the incident waves and amplitude of transmitted and reflected waves are studied. The possibility of using the scattering-induced wave phenomena to indicate changes in crack distribution in a fault zone, possibly associated with seismicity, is discussed.
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