Variations of the amplitudes of reflections from old oceanic basement in the North Atlantic

Abstract

A study of the amplitudes of wide‐angle reflections from the sediment‐basement interface of old oceanic crust shows that the uppermost portion of layer 2 is homogeneous on the 0.15–1.00 km scale but not on the 3.0–8.0 km scale. The amplitude versus range patterns of the basement reflections recorded on 30 seismic lines were examined; most patterns are affected by the rough topography of the sediment‐basement interface. Three lines have smooth travel time curves and appear to be unaffected by topography. The amplitude patterns of these lines are different from each other; they can be modeled by synthetic seismograms computed from velocity structures which have different thicknesses of a transition zone between the limestone sediments and the basaltic crust.

Shallow structure of oceanic crust in the western North Atlantic from seismic waveform inversion and modeling

“…Several studies using surface seismic data have concentrated on the sediment-basement transition [White, 1979; White and Stephen , 1980;Rohr, 1987], and these studies indicate that this transition varies from a sharp discontinuity to a gradient zone up to 300 m thick. Wide-angle expanding spread profile (ESP) data from the same region indicate the presence of first-order velocity discontinuities in this depth interval.…”