Characterizing average properties of Southern California ground motion envelopes G. Cua and T. H. Heaton Abstract We examined ground motion envelopes of horizontal and vertical acceleration, velocity, and filtered displacement recorded within 200 km from Southern California earthquakes in the magnitude range 2 < M <= 7.3. We introduce a parameterization that decomposes the observed ground motion envelope into P-wave, S-wave, and ambient noise envelopes. The body wave envelopes are further parameterized by a rise time, a duration, a constant amplitude, and 2 coda decay parameters. Each observed ground motion envelope can thus be described by 11 envelope parameters. We fit this parameterization to 30,000 observed ground motion time histories, and develop attenuation relationships describing the magnitude, distance, frequency band, and site dependence of these 11 envelope parameters. We use these attenuation relationships to study 1) magnitude-dependent saturation of peak amplitudes on rock and soil sites in various frequency bands, 2) magnitude and distance scaling of P- and S-waves, and 3) the reduction of uncertainty in predicted ground motions due to the application of site-specific station corrections. We compare our envelope amplitude attenuation relationships with amplitude levels predicted by strong motion attenuation relationships in the literature.