Mostaccio, Antonino

In questo lavoro viene descritta la sismicità, collegata agli eventi vulcanotettonici, registrata dalle stazioni della Rete Sismica Permanente dell’INGV – Osservatorio Etneo (OE) nell’area vulcanica del Monte Etna dall’1 gennaio al 31 dicembre 2020. Nel periodo di riferimento la rete sismica gestita dall’INGVOE risulta costituita da un centinaio di stazioni i cui segnali sismici sono trasmessi in tempo reale al CUAD (Centro Unificato Acquisizione Dati) di Catania dove vengono acquisiti e trasferiti in continuo alla Sala Operativa dell’Osservatorio Etneo. Nel corso del 2020 sono stati registrati 3604 terremoti, di cui 2287 localizzati dal Gruppo di Lavoro Analisi Dati Sismici dell’OE (GLAOE), secondo gli standard definiti per la compilazione del catalogo strumentale nell’ambito delle attività di monitoraggio previste all’interno dell’Accordo Quadro INGV – Dipartimento Protezione Civile (DPC) 20122021 (Allegato A). Le profondità focali degli eventi analizzati sono comprese tra 1.6 e 35 km circa, mentre la magnitudo locale (ML) risulta compresa tra 0.2 e 3.7; la magnitudo di completezza (MC) del risultante catalogo è pari a 1.2 (± 0.01), valore quindi del tutto confrontabile con quello stimato per il 2017 e il 2019, ma superiore di 0.1 unità rispetto a quello stimato per il 2018. Sono 15 gli eventi con ML ≥ 3.0 registrati nel corso del 2020, la maggior parte dei quali appartenenti alle 11 sequenze sismiche che sono state individuate per lo stesso anno. La sequenza sismica più importante sia per numero di eventi (21) sia per energia rilasciata (valore massimo ML = 3.7), è stata registrata il 31 dicembre a partire dalle 19:59 (UTC) e ha interessato il medio versante meridionale dell’edificio vulcanico, poco a nord del centro abitato di Ragalna.

Sono analizzati ed elaborati i dati dei rilievi macrosismici relativi ai terremoti verificatisi in Sicilia nel periodo 2014­2018. Si tratta di eventi che hanno provocato effetti macrosismici di rilievo e/o danneggiamento per la maggior parte localizzati nell’area etnea, cui si aggiungono alcuni terremoti di magnitudo moderata verificatisi nei settori ibleo e eoliano. I dati sono stati raccolti e elaborati secondo il protocollo del gruppo operativo QUEST (QUick Earthquake Survey Team) dell’INGV, e successivamente parametrizzati secondo gli standard adottati per la compilazione del catalogo CPTI e della banca dati macrosismica DBMI.

3D earthquake locations, focal mechanisms and stress tensor distribution in a 16- month interval covering the 2018 Mt. Etna flank eruption, enabled us to investigate the relationship between magma intrusion and structural response of the volcano and shed light on the dynamic processes affecting the instability of Mt. Etna. The magma intrusion likely caused tension in the flanks of the volcano, leading to significant ground deformation and redistribution of stress on the neighbouring faults at the edge of Mt. Etna's unstable sector, encouraging the ESE sliding of the eastern flank of the volcano. Accordingly, FPSs of the post-eruptive events show strike slip faulting mechanisms, under a stress regime characterized by a maximum compressive σ1, NE-SW oriented. In this perspective, any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano.

Instrumental seismic catalogues are an essential tool for the zonation of the territory and the production of seismic hazard maps. They are also a valuable instrument for detailed seismological studies regarding active volcanoes and, above all, for interpreting the magma dynamics and the evolution of eruptive phenomena. In this paper, we show the first instrumental earthquake catalogue of Mt. Etna, for the period 2000-2010, with the purpose of producing a homogeneous dataset of 10 years of seismological observations. During this period, 16,845 earthquakes have been recorded by the seismic network run by the Istituto Nazionale di Geofisica and Vulcanologia, Osservatorio Etneo, in Catania. A total of 6,330 events, corresponding to approximately 40% of all earthquakes recorded, were located by using a one-dimensional VP velocity model. The magnitude completeness of the catalogue is equal to about 1.5 for the whole period, except for some short periods in 2001 and 2002-2003 and at the end of 2009. The reliability of the data collected is supported by the good values of the main hypocentral parameters through the time. The spatial distribution of seismicity allowed the highlighting of several seismogenetic areas characterized by different seismic rates and focal depths. This seismic catalogue represents a fundamental tool for several research aiming to a better understanding of the behavior of an active volcano such as Mt. Etna.

Sono analizzati ed elaborati i dati dei rilievi macrosismici relativi ai terremoti verificatisi in Sicilia nel periodo 2009-2013. Si tratta di eventi che hanno provocato effetti macrosismici di rilievo e/o danneggiamento per la maggior parte localizzati nellâ area etnea, cui si aggiungono alcuni terremoti di magnitudo moderata, legati a sequenze sismiche significative verificatisi nei settori ibleo, peloritano e eoliano. I dati sono stati raccolti e elaborati secondo le procedure operative di prassi adottate in questi casi dal gruppo QUEST (ex-TTC 1.11 â Osservazioni e monitoraggio macrosismico del territorio nazionaleâ ) dellâ INGV, e successivamente parametrizzati secondo gli standard adottati per la compilazione del catalogo CPTI e banca dati macrosismica DBMI (ex-TTC 5.1 â Banche dati e metodi macrosismiciâ ).

The increasing accuracy of 3D velocity models developed recently for Mt. Etna has enabled their use today in routine earthquake locations. In this work, we tested the potential and performance of a global-search probabilistic earthquake location method (NonLinLoc) in a 3D velocity model, to improve earthquake locations for seismic surveillance. In addition, NonLinLoc hypocenter locations and those obtained by standard iterative-linear 3D locations, SimulPS-14, have also been compared. To this end, a dataset of 328 selected earthquakes, occurring during the 2002–2003 Etna flank eruption, and the recent highest resolution 3D velocity model, have been used. The results revealed that the differences in hypocentral coordinates between the two methods are typically of the same order or smaller than the spatial location uncertainty. To evaluate the consistency of results between the two 3D location algorithms, synthetic datasets with real source–receiver configuration are also considered. Furthermore, by using NonLinLoc we estimated the influence of the source–receiver geometry on the quality of hypocenter locations. If we vary the network geometry in a dense and well-distributed network like at Etna, reducing the number of stations (by 20% and 50%), it is significant that no large systematic hypocentral shifts of the relocated earthquakes are observed if they occur within the network. NonLinLoc is a fast and promising approach for automatic earthquake locations and surveillance purposes at Mt. Etna, because (1) it works well with a reduced number of seismic pickings, which are usually available in the automatic locations; (2) it is not particularly sensitive to tolerable levels of random noise in arrival times; and (3) it produces full location uncertainty and resolution information with respect to standard iterative-linear 3D locations.

The Pernicana–Provenzana Fault System is one of the most active tectonic systems of Mt. Etna and it plays an important role in the dynamic of the eastern flank of the volcano. Earthquakes occurring close to this structural trend have reached magnitudes up to 4.2, sometimes with coseismic surface faulting, and have caused severe damages to tourist resorts and villages in the vicinity of this structure. In the last decade, a large number of shocks, sometimes in the form of swarms, linked to Pernicana–Provenzana Fault System movements have been detected by the permanent local seismic network operating in eastern Sicily. In this paper, we report on the detailed study of the seismic activity occurring during the 2000–2009 time span in the Pernicana–Provenzana Fault System area. Firstly, we located 407 earthquakes using a standard location code and a 1D crustal velocity model. We then applied two different approaches to calculate precise hypocenter locations of the events. In particular, a non-linear code was adopted to obtain an estimate of the a posteriori Probability Density Function in 3D space for the hypocenter location. Moreover, a relative location of correlated event pairs was performed, using the double-difference method. These two different location approaches allowed defining with good accuracy, the most active and hazarding sectors of the structure. The results of these precise locations showed a tighter clustering in the epicenters and in focal depths, in comparison with standard locations. Earthquakes are located along the Pernicana–Provenzana Fault System, and are mainly clustered in two zones, separated by an area with very low rate of earthquakes occurrence, but characterized by the highest energy release. Depths of the foci are very shallow, ranging between the surface and about 3 km b.s.l. Kinematics of the Pernicana–Provenzana Fault System, revealed by the fault plane solutions computed for the most energetic earthquakes, highlights a predominant dip–slip and left strike movements along E–W oriented fault planes, in agreement with field observations.

Automatic procedure for locating earthquake in quasi-real time must provide a good estimation of earthquakes location within a few seconds after the event is first detected and is strongly needed for seismic warning system. The reliability of an automatic location algorithm is in[U+FB02]uenced by several factors such as errors in picking seismic phases, network geometry, and velocity model uncertainties. On Mt. Etna, the seismic network is managed by INGV and the quasi-real time earthquakes locations are performed by using an automatic-picking algorithm based on short-term-average to long-term-average ratios (STA/LTA) calculated from an approximate squared envelope function of the seismogram, which furnish a list of P-wave arrival times, and the location algorithm Hypoellipse, with a 1D velocity model. The main purpose of this work is to investigate the performances of a different automatic procedure to improve the quasi-real time earthquakes locations. In fact, as the automatic data processing may be affected by outliers (wrong picks), the use of a traditional earthquake location techniques based on a least-square misfit function (L2-norm) often yield unstable and unreliable solutions. Moreover, on Mt. Etna, the 1D model is often unable to represent the complex structure of the volcano (in particular the strong lateral heterogeneities), whereas the increasing accuracy in the 3D velocity models at Mt. Etna during recent years allows their use today in routine earthquake locations. Therefore, we selected, as reference locations, all the events occurred on Mt. Etna in the last year (2011) which was automatically detected and located by means of the Hypoellipse code. By using this dataset (more than 300 events), we applied a nonlinear probabilistic earthquake location algorithm using the Equal Differential Time (EDT) likelihood function, (Font et al., 2004; Lomax, 2005) which is much more robust in the presence of outliers in the data. Successively, by using a probabilistic non linear method (NonLinLoc, Lomax, 2001) and the 3D velocity model, derived from the one developed by Patanè et al. (2006) integrated with that obtained by Chiarabba et al. (2004), we obtained the best possible constraint on the location of the focii expressed as a probability density function (PDF) for the hypocenter location in 3D space. As expected, the obtained results, compared with the reference ones, show that the NonLinLoc software (applied to a 3D velocity model) is more reliable than the Hypoellipse code (applied to layered 1D velocity models), leading to more reliable automatic locations also when outliers are present.

On April 6, 2009 a Mw 6.3 earthquake heavily damaged the city of L'Aquila, its suburbs and several localities along the Aterno valley. The extent of the damage was the result of several factors, among which the high vulnerability of the ancient buildings but in some cases also of the modern ones, the structure of the urban centres and the site effects deriving from local critical geological conditions. We present the results of the macroseismic investigation carried out in the epicentral area by using the European Macroseismic Scale (EMS), a more suitable scale than the Mercalli-Cancani-Sieberg (MCS) one in evaluating rather complex damage scenarios. The maximum intensity has been estimated for Onna (IX EMS), the historical centre of L’Aquila, and for Castelnuovo, Pettino and S. Elia (VIII-IX EMS). On the whole, some 30 localities within an area that extends for 35 km in a NW-SE direction suffered significant damage (VII-VIII EMS). Finally, we discuss the differences in the intensity assessment deriving from the interpretation of the MCS and EMS scales.

The analysis of seismicity due to the activation of Pernicana Fault in the period 1999-2009 (about 400 earthquakes) has provided useful information for the characterization of this structure. By applying different techniques of location and analysis of cross-correlation on waveforms of earthquakes, it was possible to highlight that the Pernicana Fault is actually composed of segments characterized by different releases of seismic energy. Moreover, the space-time analysis of the evolution of the seismicity showed evident correlation with the eruptive activity of the volcano and the dynamics of its eastern flank.