9529075 Swift These investigators from Woods Hole Oceanographic Institution in Massachusetts will study existing recordings of seismic shear waves from the Costa Rica Rift region in the eastern Pacific Ocean to study the variability of acoustic and physical properties of the upper 825 meters of the basaltic ocean floor. The presence of good quality shear wave arrivals is rare in experiments carried out in this environment, and when combined with the compressional wave studies which have already been carried out from these same data, the shear waves provide important constraints on the rock properties. The data were collected as part of a vertical seismic profiler (VSP) experiment with receivers located within Deep Sea Drilling Project hole 504B, the deepest penetration ever made into the ocean crust. They provide an opportunity to define crustal properties at higher resolution than has been possible at any other location. The project was proposed following the recognition of good quality shear wave arrivals in these data, and the investigators have developed new analytical techniques which make possible the first coincident study of borehole lithology (from drilling results), borehole porosity derived from in-situ logging, and the compressional and shear velocity information which is contained in the VSP data. ***
