Seismic properties of volcanic rocks from DSDP Hole 62-465A

Hess Rise, a major structural feature in the northern Pacific, is one of several oceanic plateaus which apparently possess anomalous seismic structures (Sutton et al., 1971). Hence, Laboratory measurements of compressional- and shear-wave velocities in rocks from oceanic plateau regions are of considerable interest. Several questions come to mind: (1) Are compressional - wave velocities of volcanic rocks from oceanic plateaus similar to basalts of equivalent age from normal oceanic crust? (2) Do velocity-density relations for plateau rocks fit the well-established trends for Layer 2 basalts? (3) How do Poisson's ratios, determined from compressional- and shear-wave velocities, of oceanic plateau rocks compare with those of normal sea-floor basalts?
To answer these questions, we have selected for velocity measurements five volcanic samples from different depths from Hole 465A, on southern Hess Rise. It is particularly significant that all the rocks are vesicular and have been highly altered, which significantly affects their elastic properties.