Abstract
An oblique seismic experiment (OSE) was carried out at Ocean Drilling Program (ODP) Hole 418A in the western North Atlantic to investigate vertical, lateral, and azimuthal structural variations in the upper portions of relatively old ocean crust. Original analysis of the data for travel time anisotropy did not show systematic azimuthal trends in seismic structure except at shallow depths immediately adjacent to the borehole. Subsequent analysis of the OSE data, presented here, reveals a correlation between scattering strengths versus azimuth and spreading direction of the crust. Analyses are performed on body and coda waves and include coda energy and normalized coda energy calculations, spectral analysis, coda dropoff rates, and cross‐correlation analysis. All of the analyses show trends indicating an increase in seismic scattering along directions parallel to the paleospreading direction. These results suggest that evidence of crustal formation processes is still present and seismically detectable after 108 m.y. of crustal evolution. Scattering is likely caused by crustal cracks and/or aligned heterogeneities indicating that either large crustal cracks are still present in the crust or that homogenization of the crust through hydrothermal deposition of secondary minerals is not complete at this site.
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