Massucci, Angelo

Since 2018, INGV funded 3 projects aimed to detect ground deformations and gravity variations over different timescale in the area where the recent seismic events of L’Aquila (2009, Mw 6.3) and Amatrice-Norcia (2016, Mw 6.1 and 6.5) took place. The consequent static deformation field reached several centimetres and the modelled impact of such events could have modified the gravity field up to 170 μGal. Furthermore, the medium-long-term gravity and ground deformation variations related to post-seismic relaxation are expected as consequence of vertical deformation of the Earth surface and/or of the internal boundaries separating layers at depth with different densities. In addition, the L’Aquila area is affected by deformations induced by ground water level changes in the aquifers. Therefore, a multidisciplinary approach carrying out joint measurements of deformation and gravity is fundamental to understand the role of each geophysical process. To this aim, a network of 3 (Terni, Popoli, Sant’Angelo Romano) new non-permanent GNSS stations was realized outside the buildings hosting the absolute gravity stations. At L’Aquila, a permanent GNSS station managed by the Italian Space Agency (AQUI) is continuously working on the rooftop terrace of the Science Faculty, and positioned vertically with respect to the gravimetric station (AQUIg), which is located 4 floors below. Since 4 absolute gravimetric sites are located indoor, the precise coordinates of the gravity benchmark have been obtained by classical topographic surveys, connecting the indoor site to the outdoor GNSS reference point. Here we present the gravity and ground deformation variations observed in the period 2018-2022 after five measurement campaigns.

Crustal deformations are widely studied in Italy by analyzing data from GNSS permanent networks. However, deformations can be generated by very different geophysical processes related to tectonics but also to fluid circulation and density variations. Therefore, it is very important to understand if the detected deformations are connected to gravity variations (Greco et al., 2021a). Since 2018, INGV funded 3 projects aimed to detect ground deformations and gravity variations over different timescale in the area where the recent seismic events of L’Aquila (2009, Mw 6.3) and Amatrice-Norcia (2016, Mw 6.1 and 6.5) took place. The consequent static deformation field reached several centimetres and the modelled impact of such events could have modified the gravity field up to 170 μGal (Riguzzi et al., 2019). Furthermore, the medium-long-term gravity and ground deformation variations related to post-seismic relaxation are expected as consequence of vertical deformation of the Earth surface and/or of the internal boundaries separating layers at depth with different densities. In addition, the L’Aquila area is affected by deformations induced by ground water level changes in the aquifers (Devoti et al., 2018). Therefore, a multidisciplinary approach carrying out joint measurements of deformation and gravity is fundamental to understand the role of each geophysical process. To this aim, a network of 3 (Terni, Popoli, Sant’Angelo Romano) new non-permanent GNSS stations was realized outside the buildings hosting the absolute gravity stations (Greco et al., 2021b). At L’Aquila, a permanent GNSS station managed by the Italian Space Agency (AQUI) is continuously working on the rooftop terrace of the Science Faculty, and positioned vertically with respect to the gravimetric station (AQUIg), which is located 4 floors below (Fortunato et al., 2020). Since 4 absolute gravimetric sites are located indoor, the precise coordinates of the gravity benchmark have been obtained by classical topographic surveys, connecting the indoor site to the outdoor GNSS reference point. In the poster we describe the procedure and results followed to achieve the coordinates of both the GNSS and the absolute gravimetric sites. Furthermore, we also present the results over the short and the medium-long-term obtained by repetitive combined GNSS and integrated absolute and relative gravity measurements.

A first combined absolute gravity and GNSS network of 5 stations distributed between Lazio, Umbria and Abruzzo regions, was realized in 2018 in order to lay the basics for a multidisciplinary approach to natural risk assessment in the area of Central Italy, affected by the 2009 and 2016 seismic activity. Up to now, two absolute gravity campaigns were carried out using the transportable Microg LaCoste FG5#238 and the portable A10#39 absolute gravimeters. The locations of gravimetric sites have been chosen indoor to allow optimal condition of measure; therefore, the heights of the indoor sites have been determined by joining the outdoor GNSS with classical topographic surveys. The good results obtained after the campaigns and data processing lay the foundations for a new multidisciplinary approach to study also seismogenetic areas. In this paper, we present the gravity and GNSS station monographs, together with the absolute gravity values and the coordinates resulting from the first field surveys.

We investigated the interseismic GPS velocity field across the transition zone between Central and Southern Apennine comprising the Meta–Mainarde-Venafro and Alto Molise–Sannio-Matese mounts. The kinematic field obtained by combining GPS network solutions is based on data collected by the unpublished episodic campaigns carried out on Southern Apennine Geodetic network (SAGNet from 2000 to 2013), IGM95 network (Giuliani et al., 2009 from 1994 to 2007) and continuous GPS stations. The data collected after the 29 December 2013 earthquake (Mw 5.0) until early 2014 allowed estimating displacements at 15 SAGNet stations. The extension rate computed across the Matese massif along an anti-Apennine profile is 2.0±0.2 mm/yr. The interseismic velocities projected along the profile show that the maximum extension does not follow the topographic high of the Apennines but is shifted toward the eastern outer belt. No significant GPS deformation corresponding to inner faults systems of the Matese massif is detected. Taking into account our results and other geophysical data, we propose a conceptual model, which identifies the 2013–2014 seismic sequence as not due to an extensional deformation style usual along the Apennine chain. In fact, we have measured too large “coseismic” displacements, that could be explained as the result of tectonic regional stress, CO2-rich fluid migration and elastic loading of water in the karst Matese massif. We recognized a tensile source as model of dislocation of 2013–2014 earthquakes. It represents a simplification of a main fault system and fracture zone affecting the Matese massif. The dislocation along NE-dipping North Matese Fault System (NMFS) could be the driving mechanism of the recent seismic sequences. Moreover, to the first time the SAGnet GPS data collected from 1994 to 2014, are share and available to the scientific community in the open access data archive.

We investigated whether the joint inversion of geodetic and stress direction data can constrain long‐term fault slip rates in the central Apennines, and ultimately how extension is partitioned among fault slip and bulk lithosphere permanent strain. Geodetic velocities are collected in the fault interseismic stage with steady secular deformation; thus, long‐term estimates can be derived with a model of elastically unloading seismogenic faults within a viscously deforming lithosphere. As the average spacing of permanent Global Navigation Satellite Systems (GNSS) stations is similar to the average length of seismogenic faults (25–35 km), if not larger, we decided to merge permanent and temporary GNSS measurements, resulting in a denser geodetic data set. Given that most normal faults in the Apennines have slip rates around or below 1 mm/a, and most campaign GNSS velocities carry similar uncertainties, simple local back slip models cannot be applied. More sophisticated modeling is required to extract reasonable bulk deformation rates and long‐term fault slip rates at signal‐to‐noise ratio of order unity. Given the spatial distribution of the GNSS network, we estimated the long‐term slip rate of seven major fault systems that are in satisfactory agreement with available geological slip rates. The resulting spatial distribution of bulk deformation rates locally fits short‐term transients; in other cases, they represent the currently unclear signature of tectonic processes like upper‐crustal viscoplastic deformation and aseismic slip, or indicate missing faults in the adopted database. We conclude that the time is ripe for determining fault slip rates using geodetic and stress direction data, particularly where fault activity rates are hard to determine geologically.

L’attività presentata è parte del Progetto dal titolo “Feasibility of an absolute gravity network in central Italy: toward a multi-disciplinary approach to natural risk assessment”, finanziato dall’Istituto Nazionale di Geofisica e Vulcanologia (INGV) nell’ambito dei Progetti di Ricerca Libera finalizzati allo studio e al monitoraggio dei rischi naturali dell’Italia Centrale. Lo scopo del progetto è la realizzazione di una rete gravimetrica, assoluta e relativa, e di stazioni GPS a larga scala in Italia Centrale, nelle aree interessate dalla più recente attività sismica, e di gettare le basi per un approccio multidisciplinare alla valutazione del rischio naturale. La fattibilità del progetto è stata possibile per la disponibilità presso l’INGV di due gravimetri assoluti, uno da laboratorio (Micro-g LaCoste FG5#238) e uno da campagna (Micro-g LaCoste A10#39). La finalità principale del progetto è quella di rilevare, mediante l’occupazione di siti già esistenti sul territorio e misurati in passato, eventuali variazioni della gravità e di deformazioni del suolo occorse su lungo periodo. Dopo una ricerca sull’esistenza di vertici gravimetrici e GPS nel territorio, di interesse per il progetto, e a seguito di sopralluogo, sono stati selezionati 5 siti distribuiti tra Lazio e Abruzzo, come illustrato nella Fig.1. Figura 1: Distribuzione delle stazioni selezionate per misure gravimetriche e GPS in Centro Italia. Due vertici di misure relative (Terni e Popoli), appartenenti alla rete del rilievo gravimetrico condotto dall’ING nel 1954 (Morelli, 1955), sono stati collegati a due stazioni assolute instituite nell’ambito del presente progetto nella stessa area; la stazione assoluta di Sant’Angelo Romano è stata istituita nel 2005 nell’ambito di un Progetto di Ricerca INGV-DPC sui Colli Albani (Berrino et al., 2006; Riguzzi et al., 2007; D’Agostino et al., 2008); un sito per misure relative presso i laboratori superficiali dei Laboratori Nazionali del Gran Sasso (LNGS) istituito nel 2010 nel corso di indagini svolte a seguito dell’evento sismico del 2009 e quando fu contemporaneamente realizzata anche una stazione assoluta nel centro della città di L’Aquila (Berrino et al., 2010); la stazione assoluta all’Aquila presso l’Università di Coppito è stata istituita nel corso del presente progetto in sostituzione di quella realizzata nel 2010 attualmente non occupabile. La prima campagna di misure è stata effettuata nella seconda metà di giugno 2018 durante la quale sono state effettuate: a) misure assolute dell’accelerazione di gravità, con il solo gravimetro FG5#238 per indisponibilità dell’A10#39; b) misure gravimetriche relative per i collegamenti tra i vari vertici assoluti e le rispettive stazioni satelliti relative, e per la misura del locale gradiente verticale della gravità nelle stazioni assolute; c) misure GPS e topografiche classiche per il posizionamento dei siti di misura e il riporto della quota, anche da capisaldi altimetrici dell’IGMI dove esistenti. Una seconda campagna di misura è stata svolta tra la fine di settembre e gli inizi di ottobre 2018 durante la quale sono state effettuate solo misure assolute di gravità, ma con entrambi i gravimetri disponibili, e ulteriori misure GPS e topografiche classiche. Nel corso della seconda campagna, data la possibilità dell’utilizzo del gravimetro assoluto da campagna, è stata anche effettuata la misura assoluta sul sito relativo dei LNGS superficiali. L’utilizzo congiunto dei due gravimetri permette la loro inter-comparazione, utile allo scopo di poter effettuare le misure assolute anche separatamente in qualsiasi altra eventuale occasione che comporta l’utilizzo di più strumenti. Il gravimetro FG5#238 è stato già più volte inter-comparato con il gravimetro di riferimento italiano (Jiang et al., 2012; Greco et al., 2015; Pálinkáš et al., 2017), che è il gravimetro Standar Primario IMGC-02 realizzato presso l’Istituto Nazionale per la Ricerca Metrologica (INRiM) di Torino; mentre per l’A10 è in fase di attuazione l’inter-comparazione direttamente presso i Laboratori dell’INRiM. L’inter-comparazione tra strumenti è, come ben noto, fondamentale per l’omogeneizzazione dei dati, e la procedura seguita rientra nelle indicazioni date nel 2014 dalla Consultive Committee for Mass and related quantities (CCM) della International Association of Geodesy (IAG) (CCM-IAG Strategy for Metrology in Absolute Gravimetry). Alcune delle stazioni assolute misurate nel presente progetto faranno parte della Rete Gravimetrica Italiana di Riferimento “G0”, che è in fase di progettazione e che sarà costituita da sole stazioni assolute della gravità opportunamente misurate e/o rimisurate. Sebbene i dati raccolti siano ancora in corso di analisi, i risultati ottenuti hanno permesso di evidenziare le variazioni di gravità e di quota occorse ai singoli vertici, sia con riferimento al periodo relativo all’istituzione di ciascun vertice (relativo o assoluto) che tra le due campagne; e in particolare, dall’analisi congiunta dei dati gravimetrici assoluti e relativi, è stato possibile confermare il bias di circa -14 mGal alla stazione di Potsdam, utilizzata come riferimento nella maggior parte dei rilievi gravimetrici condotti in Italia sin dagli anni ’50. Saranno presentati, discussi e analizzati i risultati preliminari ottenuti dalle indagini effettuate.

The GPS results are of utmost relevance for the study of the complex plate boundary geodynamics. The lithosphere strain partitioning is part of the seismic cycle. We present the first GPS kinematic pattern obtained during the interseismic phase by a dense episodic GPS network, the Southern Apennine Geodetic Network - SAGNet (Sepe et al., 2009), in the time span 2002-2013. This network is located across the transition zone between central and southern Apennine, including Meta-Mainarde-Venafro and AltoMolise-Sannio-Matese mounts. This region is characterized by seismogenic fault systems responsible, in the past, for several destructive earthquakes of intensity I ≥ IX MCS and, in more recent years, characterised mainly by some moderate magnitude seismic sequences (max magnitude Mw 5.0, December 29 2013) and single small events (Ml < 2.5).SAGNet GPS data were processed by BERNESE sw v.5.0 and the resulting velocities were least-squares combined with the permanent stations velocity field and with the velocity solution of Giuliani et al. 2009. The combined GPS velocity field, shows a perpendicular maximum extension with respect to the Apennine chain of about 2.0 mm/y.The Matese area was hit on December 29, 2013 by a Mw=5.0 (Convertito et al., 2016) earthquake. It was followed by an intense seismic activity until the beginning of February 2014. After the mainshock a GPS survey was carried out on the SAGnet stations. We collected data from 2013, 30 December to 2014, 4 April. The time series of 17 stations are affect by an offsets on the linear drift. The map of horizontal coseismic displacements (Figure 3) shows a sub-radial displacement shape with respect to the epicentre. Larger displacements are observed in correspondence of NE portion of the Matese massif. Considering the Matese Lake Fault as the probable source of the mainshock (dip 65°, strike 116, rake 270 – MLF, Ferranti et al, 2015), we found that the Okada modelling does not fit the observed displacements and only a small fraction of displacements are resolved with a simple slip.Figure 4 resembles the results of previous studies compared with our GPS analysis. We considered seismological analyses, tomographic models, degassing of CO2 data and conceptual model of processes recognized in South Apennine (L. Bisio, et al., 2004; Chiarabba and Chiodini, 2013; Improta et al., 2014; Ventura et al., 2007, R. Di Stefano and M.G. Ciaccio, 2014; Ferranti et al., 2015; Convertito et al., 2016;). The GPS results indicate that the relative motion between Eurasia and Adria plates is responsible of the active deformation in the Apennines. The most important outcomes of this study are: (i) During the interseismic phase the differential motion between Adriatic and Tyrrhenian domains seems to be accommodated in a narrow belt bordering the westward flank of the Sannio Mts, showing a 2 mm/y extension. (ii) The maximum extension does not follow the topographic high of the chain but is shifted toward the eastern outer belt. (iii) No significant GPS deformation is highlighted in correspondence of major and known fault systems where the GPS velocities appear almost steady. We propose that the observed coseismic displacements are only marginally explained by a slip on the MLF fault. The vertical directivity and depth distribution of the seismic sequence (Convertito et al., 2016), the vertical and horizontal heterogeneity of lower crust and upper mantle (Bisio et al., 2004; Di Stefano and Ciaccio, 2014), the high flux of CO2 degassing (Ventura et al., 2007, Chiarabba e Chiodini, 2013 ), the probable presence of pressurized CO2 bodies fed by fluids uprising from the mantle wedge (Improta et al.,2014 ), suggest instead that the seismic sequence could be caused by sub-vertical cracks that originate at the Moho interface and reach the bottom of the seismogenic layer (10km depth).

We used continuous Global Positioning System (GPS) measurements to infer the fault geometry and the amount of coseismic slip associated to the August 24, 2016 Mw 6 Amatrice earthquake. We realized a three-dimensional coseismic displacement field by combining different geodetic solutions generated by three independent analyses of the raw GPS observations. The coseismic deformation field described in this work aims at representing a “consensus” solution that minimizes the systematic biases potentially present in the individual geodetic solutions. Because of the limited number of stations available we modeled the measured coseismic displacements using a uniform slip model, deriving the geometry and kinematics of the causative fault, finding good agreement between our geodetically derived fault plane and other seismological and geological observations.

We used High-Rate sampling Global Positioning System (HRGPS) data from 52 permanent stations to retrieve the coseismic dynamic displacements related to the 2016 August 24 Mw 6.0 Amatrice earthquake. The HRGPS position time series (named hereinafter "GPSgrams") were obtained with two different analysis strategies of the raw GPS measurements (Precise Point Positioning [PPP] and Double-Difference [DD] positioning approaches using the Gipsy-Oasis II and the TRACK (GAMIT/GLOBK) software, respectively). These GPSgrams show RMS accuracies mostly within 0.3 cm and, for each site, an agreement within 0.5 cm between the two solutions. By using cross-correlation technique, the GPSgrams are also compared to the doubly-integrated strong motion data at sites where the different instrumentations are co-located in order to recognize in the GPSgrams the seismic waves movements. The high values (mostly greater than 0.6) of the cross-correlation functions between these differently-generated waveforms (GPSgrams and the SM displacement time-histories) at the co-located sites confirm the ability of GPS in providing reliable waveforms for seismological applications.

A ML=4.9 earthquake occurred in the Sannio-Matese area at 18:08 on December 29 2013. The epicenter was located in the “Monti del Matese seismic district”. The epicentral area lies between the small towns of San Gregorio Matese, Cusano Mutri, Gioia Sannitica, Piedimonte Matese, San Potito Sannita in the Caserta province in an area with an high seismic Hazard. The area was struck by large and destructive earthquakes in the past (1456, 1688, 1702, 1732, 1805,1962) with maximum magnitude up to 7.2. Past and recent seismicity of the area is generally characterized by both single events and low energy seismic sequences (1885, 1903, 1905, 1990, 1992, 1997). The last sequence occurred on 1997 with the largest event (MD = 4.1, 19 March) occurred at the border between the Benevento and Campobasso provinces followed by an intense activity ended only in September of the same year. The epicentral distribution of the 1997 low energy (M ≤ 4.0) seismic sequence is mainly NE-SW oriented suggesting the activation of anti-Apennine faults. The December 29 2013 seismic event, is located very close to the 1688 earthquake area. Still open debate is the association of the main event of the sequence and its aftershocks with the seismogenic structures present in the area. The SAGNET (Southern Apennine Geodetic NETwork) is the Non-permanent GPS network covering the area between the Matese Mounts and the Mainarde–Meta Mountains and consists of 40 3D GPS vertices. GPS dataset consists of data recorded at non-permanent stations in the time spam 2002-2014 and at the Continuous GPS stations (CGPS) of the RING network (managed of INGV) located in the central and southern Apennines regions. We have calculated the GPS velocity field with permanent and non-permanent stations (with time series of at least 3 surveys). The horizontal velocity field, expressed with respect to a fixed Eurasian plate, shows a good coherence between the velocities field estimated from the SAGNET and CGPS. In this paper we have evaluated the strain rate in the Sannio-Matese area. Before the earthquake, GPS data analysis showed a decrease in the velocity in the southern sector of Matese Massif (where the December 29 2013 earthquake epicenter will be localized) with respect to the surrounding areas which is also evident from the lower values of the strain rate ranging between 15÷20 *10-9 yr-1. Lower GPS Strain rate has been recognized at the end of seismic cycle and appear as a useful tool to point out hazardous seismic areas as already highlighted in the 2009 L'Aquila and in the 2012 Emilia earthquakes.