Charlotte E. (Davidson) Keen

Two experiments were undertaken; their purpose was to determine some of the physical properties of the crust and mantle beneath the ocean basin. The first experiment was a seismic refraction experiment over the continental rise near Nova Scotia. The information from this experiment was combined with that from previous seismic experiments and with measurements of gravity over the continental margin and models for the crust and upper mantle structure are presented. The models which satisfy both the seismic and gravity observations suggest that horizontal and vertical density variations occur in the upper mantle down to 100 km. The results indicate a mantle density of 3.42 g/cm3 under the continental shelf and 3.32 g/cm3 under the ocean basin.

The second experiment is concerned with the determination of the elastic parameters of the rocks from a study of the propagation properties of the refracted wave. A solution of the wave equation which describes the refracted wave was obtained. A seismic refraction experiment was conducted over the Sohm Abyssal Plain in the northwest part of the Atlantic Ocean. The wave- forms of the refracted waves observed on the seismograms have been compared with computed wave-forms corresponding to several models for the layer thicknesses and elastic parameters under the refraction profiles. The value for the specific attenuation factor, Q, within the crust is about 400 and within the mantle it is about 1000. The compressional wave velocity in the crust is 7.0 km/s and this is in agreement with one interpretation of the time-distance plots. The above results are not yet conclusive; more computations are necessary.

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Supervisors: J. E. Blanchard