Mantle reflections beneath the crestal zone of the East Pacific Rise from multi-channel seismic data

Abstract

Two 24-fold, stacked multi-channel seismic-reflection profiles show the position of the M-discontinuity nearly continuously across the East Pacific Rise near 9°N. In the past, the position of this important boundary in the oceans has been determined almost exclusively by seismic-refraction measurements. The mantle reflection events are enhanced by the process of migration which diminishes the masking effect of the sea-floor diffractions. In one crossing of the Rise crest, the mantle reflections do not parallel the topographic relief in the time section, while in the other the mantle reflections follow the sea-floor topography. The presence of mantle reflections beneath the axial zone of an active spreading center indicates that the M-discontinuity is a feature which forms nearly contemporaneously with the oceanic crust.