GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Figure 2. (a) Example of spectral inversion and source parameter joint PDF estimation. (b) Example of automatically rejected bad quality spectra and unconstrained marginal PDF ( f c parameter). Using marginal PDF has three major advantages when it comes to uncertainty estimation: (1) It accounts for parameter correlations, as it results from the integration of the joint PDF; (2) It accounts for the quantity of information available in the frequency domain (frequency bandwidth), as larger uncertainties are associated to narrower frequency band (Supino et al., 2019); (3) It allows to automatically rejects bad quality spectra, which results in unconstrained PDF solution(s) (Fig. 2b). Results We observe a self-similar scaling between f c and M 0 for M w larger than ~2.0. For smaller magnitudes, S-wave spectra show an almost constant (~10 H Z ) corner frequency, which does not scale with the earthquake source (seismic moment) (Fig. 3a). We interpret this constant f c as the constant cut-off frequency of the anelastic attenuation, which acts as a low-pass filter and produces an apparent corner frequency. The latter is lower than expected, and corresponds to an apparent larger source duration.