In this paper, we describe observational constraints on the scaling of earthquake source parameters. To first order, parameters such as rupture area, rise time, and the size and strength of asperities (regions of large slip) scale in a self-similar manner. The near fault rupture directivity pulse is a narrow band pulse whose period increases with magnitude. Current ground motion models, which all assume monotonically increasing spectral amplitude at all periods with increasing magnitude, do not provide an accurate description of near fault ground motions. The ground motions from buried faulting are consistently stronger than those from earthquakes having large surface slip.