Being tied to a physical quantity, moment magnitude () should be the reference estimate of earthquake size and used whenever possible. Local magnitude () represents a simple alternative for a reliable estimate of size, its best use being either for quick outcomes or when the computation of is difficult (e.g., for small earthquakes). However, and are profoundly different and not interchangeable.
Here, we analyze a large set of 1509 – data points from earthquakes of the central and northern Apennines (CNA), quantify the empirical scaling, and look for features of global validity. Our data set is made of 449 unpublished s from moment tensor solutions of events from the Amatrice‐Visso‐Norcia (AVN) sequence, 170 published s from moment tensor solutions of events from the L’Aquila seismic sequence (2009), and 890 published – data points from earthquakes of the Altotiberina fault (ATF, 2010–2014; s from spectral correction). We integrate our empirical data set by computing the local magnitudes of the events from the AVN and L’Aquila sequences.
Finally, a synthetic study calibrated on the crustal attenuation and the source characteristics of the AVN data set reproduces the observed scaling between and , predicting that s in the analyzed region saturate above . Smooth transitions are predicted between the different regimes.