Seismic velocities, densities, and porosities of Layer 2B and Layer 2C basalts from Hole 504B.

Abstract

Compressional and shear wave velocities at confining pressures to 6kb, densities, and porosities were measured for 32 samples obtained from 836-1350m below seafloor (BSF) in Hole 504B, the section drilled on Leg 83 of the Deep Sea Drilling Project. These data in combination with similar measurements on 28 basalt samples from the section from 274.5-836m, drilled on Legs 69 and 70, provide a comprehensive set of physical property data for over 1000m of oceanic crust. The velocities, densities, and porosities measured in the laboratory exhibit greater variability in the upper portion of the hole. In general, compressional and shear wave velocities and densities increase with depth, reaching average values at 1kbar of Vp = 6.45km/s, Vs = 3.45km/s and rho = 2.94g/cm3 within the sheeted dike section. Porosities decrease with depth to values generally <1% near the bottom of the hole.-Authors