abstract

A plane layered oceanic crustal model is investigated. A point source and receiver are located in the oceanic fluid layer. The Mohorovic˘ić discontinuity is treated as a layered transition zone. De Hoop's modification of Cagniard's method is used to obtain the exact transient response which is convolved with the source pulse shape and the instrumental system function to yield theoretical seismograms.

When the boundary is an interface or a thin layered transition zone the head wave is a small pure refraction which is followed by a strong reflection. As the transition zone grows in thickness the head wave receives both refracted and reflected energy and becomes the dominant feature. These results compare favorably with observations made in the Bering Sea.

This study suggests that the transition zone is thin, probably less than 1 km, in the Northern Aleutian Basin. Southward approaching the Aleutian Islands the transition zone thickens so that no major discontinuity exists between the crust and mantle.

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