Influence of Source, Path, and Site Effects on the Magnitude Dependence of Ground‐Motion Decay with Distance
Résumé
We study the physical causes of the magnitude dependence of ground‐motion decay with distance that is observed on real data. Using stochastic simulations, we analyze the role played by anelastic attenuation Q (f), path duration, site effect (κ0), finite‐fault effect, and stress drop for a magnitude range between 4 and 7. We systematically look at peak ground acceleration, peak ground velocity, and pseudoabsolute spectral acceleration at different frequencies.
We find that path duration, κ0, and stress‐drop variations have a minor effect on this dependence. At close distances (typically distances smaller than the largest fault length), the main effect is the finite‐fault effect that tends to decrease the ground‐motion values of larger events. At larger distances (>30 km), it is the effect of Q (f) that is preponderant and tends to lower the ground‐motion values of smaller events.