Ground Motion Scaling in the Central Apennines

We analyzed weak motion seismograms collected between 1992 and 1999 in order to study the characteristics of excitation and propagation of seismic waves in Central Apennines. Data were provided by a network run in Abruzzo by the Servizio Sismico Nazionale (SSN). The network was made by 32 three-component digital stations (21-bit Mars88-FD) coupled with 1-Hz seismometers (Mark L4C-3D). We selected a data set of 1,200 events characterized by good signal-to-noise ratios, putting together a set of about 18,000 waveforms for the analysis. On the one hand, the entire Apennines fold-and-thrust belt was previously studied by Malagnini et al. (2000), although the set of data available at that time only allowed them to treat the entire region (from Garfagnana-Lunigiana, in the Northern Apennines, to the Calabrian Arch to the South) as structurally homogeneous. The data set described here, on the other hand, allows a detailed study on the central part of the Apennines chain, where the hypothesis of crustal homogeneity is not an overly gross approximation. The study on ground motion scaling was carried out through the techniques described by recent papers by Malagnini and co-workers, and yielded stable attenuation results. With respect to the model proposed by Malagnini et al. (2000), we described our results in terms of a slightly different geometrical spreading function and crustal attenuation parameter Q(f). Specifically, the frequency dependence of the crustal parameter Q(f) obtained in this study is higher than that previously found for the entire Apennines by Malagnini et al. (2000). The mentioned differences reflect the strong variability of the characteristics of the crust in the Apennines, both in terms of velocity structure, depth to the Moho, fluid circulation and heat flow. More studies are in progress in the Northern and Southern Apennines, in order to obtain a better understanding of the ground motion scaling in the entire fold-and-thrust belt. Regional attenuation models are being used for the compilation of a detailed hazard map of the entire Italian territory.