PEGASOS PROJECT: ESTIMATION OF THE MEDIAN, NEAR FAULT GROUND MOTION IN SWITZERLAND - SCIENTIFIC REPORT N. 6

The spectral acceleration assessed by the OGS simulations (Priolo et al., 2003) are gen- erally larger that those estimated by the SP2 experts (see for instance, Figure 1). In particular, the OGS low frequency pseudo-spectral acceleration (i.e at frequencies 1 and 0.5 Hz) features higher ampli¯cation and smoother decay. We are convinced that our method provide reliable results in that band. This was also con¯rmed by Madariaga (2002) who reported that "both OGS and URS approaches are interesting and well con- structed at low frequencies and match very well the results of rupture dynamics". Here we investigate the possible reasons of the low decay predicted at low frequencies by the OGS simulations and propose some actions to better interpret or integrate those results.