Two reference sections at Site 1044 and 1045 establish a baseline for evaluating consolidation of both the offscraped and underthrust sections up to 6 km east of the deformation front. Comparisons of the density curves from the reference sites enable calculation of underthrust sequence consolidation because of loading by the overlying accretionary prism at the LWD sites west of the deformation front. Velocity-porosity relationships could not be evaluated because of the absence of an LWD velocity tool that could measure sediments with such low velocities and the lack of time to conduct wireline velocity measurements.
Consolidation locally thins and more sharply defines the top and bottom of the low-density layer.
Producing the strong negative polarity reflections by selective consolidation contrasts with previous interpretations that invoke dilation and hydrofracture to generate the reflections. Both interpretations are viable, but the data from 171A may be more simply interpreted as a consolidation response. This pattern of arrested consolidation bears no simple relationship to the prism geometry, distance of underthrusting, or underthrust sediment form. In summary, Leg 171A partially accomplished Objective 1 by determining prism consolidation. However, we did not establish velocity-porosity relationships of these sediments.