Some thoughts on relating density to velocity

There are many occasions when density is needed for modeling of site amplification, but all that is available are values for shear-wave or compressional-wave velocity. For example, my program site_amp and Chuck Mueller’s nrattle need input of shear-wave velocity and density. I’ve built in a default relation between the two in site_amp, but I’ve never been happy with it (it is shown in a figure below, and clearly my reservations were well founded), so these notes describe my attempt to replace that relation. I’ve made use of Tom Brocher’s recent work (in particular, Brocher, 2005a, b).