The velocity structure of Layer 2 at Deep Sea Drilling Project Site 504 from logging and laboratory experiments.

Abstract

Compressional- and shear-wave velocity logs (Vp and Vs, respectively) that were run to a sub-basement depth of 1013m (1287.5m sub-bottom) in Hole 504B suggest the presence of Layer 2A and document the presence of layers 2B and 2C on the Costa Rica Rift. We conclude that the velocity structure of Layer 2 is controlled almost entirely by variations in porosity and that the crack porosity of Layer 2C approaches zero. A comparison between the compressional-wave velocities determined by logging and the formation porosities calculated from the results of the large- scale resistivity experiment using Archie's Law suggest that the velocity-porosity relation derived by Hyndman et al. (1984) for laboratory samples serves as an upper bound for Vp, and the noninteractive relation derived by Toksoz et al. (1976) for cracks with an aspect ratio alpha = 1/32 serves as a lower bound.-from Authors