GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Figure 3. (a) Scaling between corner frequency and moment magnitude. Grey circles are single event solutions, red circles are bin-averaged estimates (bin-size = 0.2 M w ) and red bars are associated weighted standard deviations. (b) Scaling between local magnitude and moment magnitude. Colors as in panel (a). The black dashed line represents a 1:1 scaling, the blue line is the best fit line for M L < 2. Because of the conservation of total displacement integral after a low-pass filtering, signals must exhibit a maximum amplitude lower than expected to “compensate” for the apparent larger source duration. However, by definition, moment magnitudes are not affected by this as they are proportional to the displacement integral (Deichmann, 2017). The comparison of our M w catalog with the local magnitude M L one proposed by Di Stefano et al. (GNGTS 2023) shows a systematic underestimation of M L with respect to M w . The deviation from a 1:1 scaling relationship between M L and M w overlaps the magnitude range where the constant apparent corner frequency arises in the M w - f c scaling ( M L < ~ 2) (Fig. 3b). Our results suggest that if we want to generate highly homogeneous earthquake catalogs especially considering the new generation ones, characterized by very low completeness magnitudes ( M c << 2), the use of local magnitudes must be reconsidered in favor of more robust estimates such as moment magnitudes. References Brune, J. N., 1970, Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res., 75 , no. 26, 4997–5009, doi: 10.1029/JB075i026p04997. Deichmann, N., 2017, Theoretical Basis for the Observed Break in M L / M w Scaling between Small and Large Earthquakes, Bull. Seismol. Soc. Am., 107, no. 2, 505–520, doi: 10.1785/0120160318. Kanamori, H., 1977, The energy release in great earthquakes, J. Geophys. Res., 82 , no. 20, 2981–2987, doi: 10.1029/JB082i020p02981.