1. The decrease in wave strength (energy per unit area of wavefront) with distance as a result of geometric spreading. A spherical wave traveling through the body of a medium continually spreads out so that the energy density decreases. For a point source the energy density decreases inversely as the square of the distance the wave has traveled; this means that the amplitude deceases linearly with the distance traveled. For energy which travels along a surface, the analogous term is cylindrical divergence, where the energy varies inversely as the distance and the amplitude as the square root of the distance. Other mechanisms by which a seismic wave loses energy involve absorption and loss at interfaces by reflection (including diffraction, mode conversion, and scattering). 2. The decrease in field strength (flux density) for gravity, magnetic, and similar fields where the intensity decreases as the square of the distance.