Effects of Local Soil, Magnitude and Distance on Empirical Response Spectra for Design

The traditional shape of design spectra, based on regions characterized by constant displacement, constant velocity and constant acceleration, has been questioned from a conceptual point of view and a new formulation based on magnitude and fault distance has been proposed in another article. The parameters required by this formulation had been derived from some 360 ground motions recorded on rock or dense soil, originated by 24 earthquakes that occurred in Italy between 1972 and 2017, with Mw between 4.5 and 6.5. This study presents an extension of the approach to all types of soil, considering a much more extended set of ground motions recorded in Europe and the Middle East (6866 records, from 387 events, Mw between 4.5 and 7.6 and stations r between 0 and 80 km). The results obtained seem to confirm that the approach is very efficient in determining response spectra for design that fit well the experimental evidence and illustrate the different effect of local soil on the amplification of acceleration and displacement. Numerous additional parameter should still be considered, such as, for example, focal depth, duration and number of significant cycles; however, the effectiveness of this approach in defining rational seismic demands is confirmed. A thorough application of this approach may result in significant re-visitation of seismic design approaches, as discussed in other articles.