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Fine structure of an oceanic crustal section near the East Pacific Rise

SEISMOLOGICAL LABORATORY DIVISION OF GEOLOGICAL AND PLANETARY SCIENCES CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIFORNIA 91125

Abstract

In this study we model synthetically a complete seismic profile of roughly 20-m.y.-old crust located to the west of the East Pacific Rise, 3.37S, 114.13W. The results indicate a rather strong velocity gradient below the sediments with little evidence of layering in the upper crust and a slightly dipping oceanic layer. The crust-to-mantle transition zone appears sharp providing a relatively good wave guide for multiple Moho reflections which are modeled synthetically to further test the usefulness of a layered earth model in explaining entire seismograms. The mantle head waves decay abruptly near 50 km which can be explained by the onset of a low-velocity zone in the upper mantle at about a depth of 12 km below the ocean surface.