Seismic properties of layer 2 basalts

Abstract

In this paper the physical properties of oceanic layer 2 basalts are examined with the emphasis on microcrack porosity and alteration-related changes in physical properties. Over 160 core samples from some of the more significant Deep Sea Drilling Project/Ocean Drilling Program holes, including 417D, 418A, 504B and 801C are included in the present investigation. Overall physical property relationships are discussed in the first half of this study. At 200 MPa confining pressure, compressionaland shear-wave velocities of the sample suite have modal values of 6.1 kms-' and 3.5 kms-', respectively. A Poisson's ratio of 0.28 characterizes the majority of the basalts. Samples that have experienced extensive low-temperature alteration, identified through elevated K,O and decreased CaO and MgO contents, exhibit low velocities (and densities) and high Poisson's ratios.