ELASTIC WAVE VELOCITIES WITHIN OCEANIC LAYER 2 FROM SONIC FULL WAVE-FORM LOGS IN DEEP-SEA DRILLING PROJECT HOLES 395A, 418A, AND 504B

Multichannel full waveform acoustic logs were recorded in Deep Sea Drilling Project (DSDP) hole 418A during Ocean Drilling Program (ODP) leg 102, DSDP hole 395A during ODP leg 109, and DSDP hole 504B during ODP leg 111, to provide nearly continuous measurements of elastic wave velocities as a function of depth within oceanic layer 2 for different spreading rates and crustal ages. The velocities depend primarily on the morphology of the basalt. Their velocities increase with depth as expected from crack closure due to confining stress. Within a given morphology the elastic properties do not depend on spreading rate. Within pillows, velocity variations depend primarily on the degree of alteration infilling and the mineralogy of the infilling material, and secondarily on conditions at emplacement. The crustal section can be separated only roughly into seismic layers on the basis of the sonic velocities. Changes in velocity with depth within the extrusive section at a single site giving rise to previously defined seismic layers 2A and 2B are due to a change with depth in the properties of the pillows, associated with differences in the amount and type of infilling materials, rather than to a change with depth in the relative proportion of pillows and massive units. -from Authors