The relationship between seismic velocity and density in the continental crust ? a useful constraint?

Abstract

Summary. Plots of seismic velocity and density of rock samples show that a range of densities is possible for rocks of each seismic velocity and vice versa, although a single linear relationship is often assumed in crustal gravity calculations. Because of the scatter, whenever rocks of known seismic velocity are converted to density using this relationship, a reduction is made to the resolving power of the resulting gravity calculation. If these rocks reach thicknesses of more than a few kilometres, then the uncertainties become significant when compared with the size of commonly observed gravity anomalies. Examples are considered from the North Sea, Mississippi and Carolina Trough. It is concluded that the use of a seismic velocity measurement as the only indication of rock density does not provide a useful constraint when attempting to reproduce observed gravity variations. An appropriate model for isostatic compensation is probably the most important factor for successful predictions of crustal structure on the basis of gravity data.