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Moment magnitude scale8/4/2023 ![]() M L values are therefore expected to be underestimated while moment magnitudes, by definition, are not affected by this as they are proportional to the displacement integral.Ĭoherently, the comparison of our M w and M L estimates shows the systematic underestimation of M L with respect to M w for small magnitude events. The latter is lower than expected, and corresponds to an apparent larger source duration.īecause of the conservation of total displacement integral after a low-pass filtering, signals must exhibit a maximum amplitude lower than expected to “compensate” the apparent larger source duration. We interpret this as the constant cut-off frequency of the anelastic attenuation, which acts as a low-pass filter and produces an apparent corner frequency. ![]() For smaller magnitudes, S-wave spectra show an almost constant corner frequency (~10 Hz), which does not scale with the earthquake source (seismic moment). We observe a self-similar scaling between f c and M 0 for M w larger than ~2.0. , obtaining M L values characterized by quality and homogeneity.īoth magnitude catalogs can be reproduced due to the availability in open databases of all the input and output parameters used for processing. We start from the same waveforms to compute local magnitude using two designed on purpose codes, PyAmp and PyML, and an attenuation law specific for the Italian region, Di Bona et al. M w is obtained from M 0 using the Kanamori equation. to estimate the a-posteriori joint probability density function of the source parameters: seismic moment M 0, corner frequency f c and high-frequency decay γ. ![]() We use the probabilistic method of Supino et al. We computed moment ( M w) and local magnitude ( M L) of about 250,000 earthquakes occurred in Italy from 2009 to 2018 and recorded at seismic stations of the Italian National Network managed by INGV.įor moment magnitude computation, we start from raw velocity waveforms and invert the displacement spectra of more than 2,000,000 S-waves manually picked. ![]()
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