The underthrust sediments from Sites 1173, 1174, and 808 follow the global velocity-porosity trends proposed by Erickson and Jarrard (1998). The formulation for normal consolidation is a better fit to the data than the high-consolidation model, as is expected for tectonically undeformed underthrust sediments.
New parameters fit to the normal consolidation model using a standard nonlinear least-squares algorithm provides a single best-fit equation that can be used to convert between velocity and porosity with reasonable uncertainty. This formulation will be used to predict porosity from seismic interval velocity for the underthrust sediments. The new formulation better predicts velocity than any of the previously determined relationships.
A critical porosity threshold appears to be crossed somewhere between Sites 1174 and 808, at ~0.30. Although a single critical porosity value can be reliably fit to the data, there are a range of porosities for which velocity exhibits a stronger dependence on porosity.