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We apply the Probabilistic Seismic Hazard Analysis (PSHA) and Physics-Based Simulations (PBS) to compute the ground motion for three dams in the Campotosto area (Central Italy). The dams, which confine an artificial water reservoir feeding hydroelectric power plants, are located in an active seismic zone between the areas that experienced the 2009 L’Aquila and 2016–2017 Central Italy seismic sequences. The probabilistic disaggregation estimated for a return period of 2475 years, corresponding to the collapse limit state for critical facilities, indicates that the most dangerous fault is associated with a maximum magnitude of 6.75±0.25 within a distance of 10 km. This fault is used in PBS to emulate the Maximum Credible Earthquake scenario. To capture the ground motion variability, we input a pseudo-dynamic source model to encompass spatial and temporal variations in the slip, rise time and rupture propagation, heavily affecting the near-source ground motion. Indeed, the ground motion above the rupture volume is mainly influenced by the epistemic uncertainties of rupture nucleation and slip distribution. The computed broadband seismograms are consistent with the near-source shaking recorded during the 2016 MW6.6 Norcia earthquake and constrain the upper bound of the simulated ground motion at specific sites. Our modelling reinforces the importance of considering vertical ground motion near the source in seismic design. It could reach shaking values comparable to or larger than those of the horizontal components. This approach can be applied in other areas with high seismic hazard to evaluate the seismic safety of existing critical facilities., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

In August 2021, an extremely productive seismic sequence took place in northeastern Italy. Within 1 month, we identified and localized 407 microearthquakes in the area monitored by the local Collalto Seismic Network. This is about 20 times the average monthly rate of events detected in the last decade; 92% of them are clustered near the village of Refrontolo at about 9 km depth (main event a ML2.5, MW2.4). None of the Refrontolo sequence earthquakes were felt by the population. The earthquakes, mostly identified by automatic procedures, were post-processed by manual picking of P, S-phases and polarities; they were localized by different techniques and define a small SE dipping volume that departs from the brittle surface previously enlightened by microseisms and assigned to the NNW dipping Montello Thrust. We interpret the sequence ruptured pre-stressed patches near to failure of sub-vertical, antithetically oriented faults. The unusual productivity rate and precursory foreshock activity support the hypothesis that the Montello system has a relevant aseismic component. We believe that this episode, of no importance from an energetic point of view, is of greatest interest for deciphering the seismic potential of this area and for strengthening automatic microearthquake detection and location procedures.

The aim of this study is the real-time generation of ShakeMaps in the southeastern Alps area. The ShakeMap software has been adapted to the southeastern Alps region and implemented to obtain a stable interface with the Antelope acquisition system in order to extract the ground-motion parameters from the waveforms and to generate ShakeMaps within 5 min of the earthquake occurrence. To evaluate the influence of the station density, synthetic seismograms are computed for the Bovec (northwest Slovenia) 2004 earthquake, and various ShakeMaps are generated by varying the grid size of the simulated recording stations. The results indicate that a dense and uniform spatial distribution of stations in the field is essential to produce accurate ShakeMaps, and the present density of stations in central Friuli is sufficient for a reliable estimate of the extent of the area of strongest shaking. The related maps are generated in real time or quasi-real time using the region-specific ground-motion predictive equations and empirical relations that predict the macroseismic intensity from the recorded ground motion. The model is validated by comparison between observed data and ShakeMap results for both weak motions (Claut 2007 earthquake) and strong motions (Bovec 1998 earthquake).

The goals of this work are to review the Northern-Italy ground-motion prediction equations (GMPEs) for amplitude parameters and to propose new GMPEs for frequency content and duration parameters. Approximately 10,000 weak and strong waveforms have been collected merging information from different neighboring regional seismic networks operating in the last 30 yr throughout Northern Italy. New ground-motion models, calibrated for epicentral distances ≤100 km and for both local (ML) and moment magnitude (Mw), have been developed starting from a high quality dataset (624 waveforms) that consists of 82 selected earthquakes with ML and Mw up to 6.3 and 6.5, respectively. The vertical component and the maximum of the two horizontal components of motion have been considered, for both acceleration (peak ground horizontal acceleration [PGHA] and peak ground vertical acceleration [PGVA]) and velocity (peak ground horizontal velocity [PGHV] and peak ground vertical velocity [PGVV]) data. In order to make comparisons with the most commonly used prediction equations for the Italian territory (Sabetta and Pugliese, 1996 [hereafter, SP96] and Ambraseys et al. 2005a,b [hereafter, AM05]) the coefficients for acceleration response spectra (spectral horizontal acceleration [SHA] and spectral vertical acceleration [SVA]) and for pseudovelocity response spectra (pseudospectral horizontal velocity [PSHV] and pseudospectral vertical velocity [PSVV]) have been calculated for 12 periods ranging between 0.04 and 2 sec and for 14 periods ranging between 0.04 and 4 sec, respectively. Finally, empirical relations for Arias intensities (IA), Housner intensities (IH), and strong motion duration (DV) have also been calibrated. The site classification based on Eurocode (hereafter, EC8) classes has been used (ENV, 1998, 2002). The coefficients of the models have been determined using functional forms with an independent magnitude decay rate and applying the random effects model (Abrahamson and Youngs, 1992; Joyner and Boore, 1993) that allow the determination of the interevent, interstation, and record-to-record components of variance. The goodness of fit between observed and predicted values has been evaluated using the maximum likelihood approach as in Spudich et al. (1999). Comparing the proposed GMPEs with SP96 and AM05, it is possible to observe a faster decay of predicted ground motion, in particular for distances greater than 25 km and magnitudes higher than 5.0. The result is an improvement in fit of about one order of size for magnitudes spanning from 3.5 to 4.5.

2006/2007 Lo scopo di questa tesi di dottorato è la stima del moto forte del suolo nell’area delle Alpi Sud-Orientali. A tal fine sono state proposte delle relazioni empiriche che stimano i parametri del moto in funzione della magnitudo, della distanza dall’epicentro e della classificazione geologica del suolo; successivamente tali relazioni sono state usate per calibrare il software ShakeMaps con il fine di generare in tempo reale le mappe di scuotimento del terreno per la regione Friuli-Venezia Giulia. Le GMPEs (Ground Motion Predictive Equations) per PGA, PGV e SA sono state calcolate nell’area delle Alpi Sud-Orientali utilizzando registrazioni del moto forte del terreno. Sono state selezionate 900 forme d’onde accelerometriche filtrate tra 0.1 Hz e 30 Hz; la distanza epicentrale varia tra 1 km a 100 km, mentre la magnitudo locale, opportunamente calibrata confrontando diversi cataloghi, varia in un intervallo relativamente ampio (3.0

We test a recently developed ShakeMap model for the Friuli Venezia Giulia (NE Italy) region (Moratto et al., 2009) by comparing the macroseismic observations, related to three past earthquakes (Cansiglio 1936, Friuli 1976 and Bovec-Krn 1998) which occurred in this region, with the instrumental intensities obtained from the ShakeMaps, and based on synthetic seismograms computed from available source models of these events. Because a comparison requires that the simulation resembles as close as possible the real situation, ShakeMaps are computed from synthetics calculated at receivers placed at the sites where the recording instruments are already operative and at the sites where the instruments are going to be installed in the near future. Since the available instrumental recordings are very few, the resulting instrumental intensity maps are compared with the macroseismic observations wherever the latter are available. We make use of various relationships between the ground motion parameters and the macroseismic intensity during the comparison. The best results are obtained when the macroseismic intensities (I ≤ VII) are estimated using the relationship proposed by Faenza and Michelini (2010).

The first stations of the Friuli Venezia Giulia (NE Italy) Accelerometric Network (Rete Accelerometrica del Friuli Venezia Giulia—RAF) were installed by the Department of Earth Sciences, University of Trieste, in the early nineties in the framework of international scientific projects. Today RAF is configured, taking in to account also other network stations operating in Italy as well as in Austria and Slovenia, to record accelerations at several important sites in the seismic area of Friuli Venezia Giulia and near its borders with Slovenia and Austria. This allows an immediate estimate of peak ground acceleration as well as a first evaluation of possible damages. In the year 2000, DST and the Friuli Venezia Giulia Direction of the Civil Defence signed an agreement for the RAF management and its use for civil defence purposes, like the prompt estimate of the damage level after an earthquake occurrence, the emergency management, the reconstruction planning, and the validation and updating of seismic hazard maps. Moreover, RAF recordings are used also for prevention purposes by the civil defence. This is performed with the computation of real time shake maps, possible ground-shaking scenarios, studies of the physics of the seismic source, site effects estimates and microzonation analyses.

On September 1976 four strong aftershocks with M > 5 occurred in the Friuli area (NE Italy) causing more damage with respect to that caused by the M6.4 mainshock that occurred on May 6, 1976. Although many studies have been published on the 1976 Friuli seismic sequence, only recently have finite-fault models based on geological considerations (Galadini et al., 2005; Burrato et al., 2008) been proposed for these aftershocks. The aim of our study is to model the September 1976 seismic sources as finite faults by computing finite-fault synthetic seismograms for several possible proposed fault models and nucleation locations. The seismicity distribution following each of the four events gives us some further information about the areal extent of the related fault and its rupture propagation. About 9000 synthetic seismograms are computed for all the tested fault models adopting the reflectivity technique for an upper cutoff frequency of 1 Hz. A “trial and error” procedure is used to find the best fit between the recorded and computed peak ground acceleration derived from signals filtered at 1 Hz, that identifies the final models. These are selected also on the basis of the existing knowledge of fault traces in the area. The four best-fit models seem to be well related to the main Barcis-Staro Selo fault system, their spatial–temporal sequence evidencing an overall progressive East-to-West migration of the seismic activity related to the 1976 sequence.