Compressional and shear wave velocities at confining pressures to 6 kb, densities, and porosities were measured for 32 samples obtained from 836 to 1350 m 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 to 836 m, drilled on Legs 69 and 70, provide a comprehensive set of physical property data for over 1000 m 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 1 kbar of V p = 6.45 km/s, K s = 3.45 km/s and p = 2.94 g/cm 3 within the sheeted dike section. Porosities decrease with depth to values generally less than 1% near the bottom of the hole.
On ODP Leg 102, the JOIDES Resolution returned to Hole 418A at the southern end of the Bermuda Rise and logged the hole with a comprehensive suite of tools to determine the geophysical properties of old oceanic crust from insitu measurements. An excellent set of density, porosity, natural gamma-ray, conductivity, resistivity, full wave and mul tichannel sonic (P and S), magnetic susceptibility, three-axis magnetometer, and caliper logs was obtained over varying intervals from 0 to 488 m within the basement. In addition, the sediments were logged through the pipe using the poros ity and spectral gamma-ray tools, water samples were taken and temperature measurements made at selected depths in basement, and the oblique seismic experiment was successfully run with a three-component borehole seismometer clamped 41, 81, 230, 330, and 430 m within the basement. The results demonstrate as follows: 1. Layer 2A is absent: V p increases gradually from 4.5 km/s at the sediment/basement contact to 6.9 km/s at 1.5 km within the basement and averages 4.8 km/s in the upper 0.5 km. 2. The upper crust is anisotropic: V p varies with azimuth by ±0.2 km/s to a range of 0.6 km, with V^ fast parallel to spreading in the top of the section and fast subperpendicular to spreading near the bottom of the hole. In addition, the upper crust displays vertical/horizontal anisotropy, with V^ fast by 0.2 km/s in the horizontal propagation direction. 3. The upper 0.5 km of the crust is cracked at all scales of investigation because Vp lab > V Plog > Vp OSE. 4. The average formation porosity of the section drilled is low (15%, of which 10% is grain boundary porosity and 5% is fracture porosity) but was originally higher by an amount less than or equal to the present volume of clay in the formation (9%). 5. The original formation porosity near the top of the section (Unit 5 and Subunit 8A) approached 40%; the origi nal velocity of this interval would have been about 3.5 km/s, or that of Layer 2A. 6. The disappearance of Layer 2A was caused by infilling by an ordered sequence of alteration products formed by rock-water interaction in a closed system.
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