SEISMIC VELOCITIES FROM THE BARBADOS RIDGE COMPLEX - INDICATORS OF HIGH PORE FLUID PRESSURES IN AN ACCRETIONARY COMPLEX

Three wide-aperture (0-5 km offset) seismic profiles were shot perpendicular to the strike of the Barbados Ridge accretionary complex at 16°12′N (line 465), 14°23′N (line 480), and 13°20′N (line 484) to image the deep structure of the accretionary complex and obtain seismic velocity data. Velocity analyses on full-fold common depth point (CDP gathers were used to provide velocity/depth functions at 1 km separation along each line to map the variation in velocity with depth and distance across the accretionary complex. Low-velocity regions are interpreted as sediments with high porosity. Where porosity is inferred to be high, pore fluid pressures are also inferred to exceed hydrostatic and pore fluids actually support the increased lithostatic load produced by recent thrusting and thickening of the complex. The correlation between the most rapidly thickened regions and the velocity anomalies suggests that a rapid rate of loading relative to the rate of pore fluid expulsion produced these overpressured sediments. -from Authors