Reflections in seismic data result from contrasts in the seismic impedance (rV) across a boundary (r is the density of the rock, V₁ and V₂ are seismic velocities on either side of the boundary).  In particular, for waves at normal incidence, the ratio R of reflected-to-incident amplitude is given by:

                                                                                        (1)

The pages found under Properties are substantially based on a report produced by the United States Department of Transportation:

Wightman, W. E., Jalinoos, F., Sirles, P., and Hanna, K. (2003). "Application of Geophysical Methods to Highway Related Problems." Federal Highway Administration, Central Federal Lands Highway Division, Lakewood, CO, Publication No. FHWA-IF-04-021, September 2003. http://www.cflhd.gov/resources/agm/