Description: Public concern about anthropogenic seismic- ity in Italy first arose in the aftermath of the deadly M ≈ 6 earthquakes that hit the Emilia-Romagna region (northern Italy) in May 2012. As these events occurred in a (tectonically active) region of oil and gas production and storage, the question was raised, whether stress perturbations due to underground industrial activities could have induced or triggered the shocks. Following expert recommendations, in 2014, the Italian Oil & Gas Safety Authority (DGS-UNMIG, Ministry of Economic Development) published guidelines (ILG - Indirizzi e linee guida per il monitoraggio della sismicità, delle deformazioni del suolo e delle pressioni di poro nell’ambito delle attività antropiche), describing regula- tions regarding hydrocarbon extraction, waste-water in- jection and gas storage that could also be adapted to other technologies, such as dams, geothermal systems, CO2 storage, and mining. The ILG describe the frame- work for the different actors involved in monitoring activities, their relationship and responsibilities, the procedure to be followed in case of variations of mon- itored parameters, the need for in-depth scientific anal- yses, the definition of different alert levels, their mean- ing and the parameters to be used to activate such alerts. Four alert levels are defined, the transition among which follows a decision to be taken jointly by relevant au- thorities and industrial operator on the basis of evalua- tion of several monitored parameters (micro-seismicity, ground deformation, pore pressure) carried on by a scientific-technical agency. Only in the case of liquid reinjection, the alert levels are automatically activated on the basis of exceedance of thresholds for earthquake magnitude and ground shaking – in what is generally known as a Traffic Light System (TLS). Istituto Nazionale di Geofisica e Vulcanologia has been charged by the Italian oil and gas safety authority (DGS- UNMIG) to apply the ILG in three test cases (two oil extraction and one gas storage plants). The ILG indeed represent a very important and positive innovation, as they constitute official guidelines to coherently regulate monitoring activity on a national scale. While pilot studies are still mostly under way, we may point out merits of the whole framework, and a few possible critical issues, requiring special care in the implementa- tion. Attention areas of adjacent reservoirs, possibly licenced to different operators, may overlap, hence mak- ing the point for joint monitoring, also in view of the possible interaction between stress changes related to the different reservoirs. The prescribed initial blank- level monitoring stage, aimed at assessing background seismicity, may lose significance in case of nearby ac- tive production. Magnitude – a critical parameter used to define a possible step-up in activation levels – has inherent uncertainty and can be evaluated using differ- ent scales. A final comment considers the fact that relevance of TLS, most frequently used in hydraulic fracturing operations, may not be high in case of trig- gered tectonic events.

Description: Published

Description: 1015–1028

Description: 1IT. Reti di monitoraggio e sorveglianza

Description: JCR Journal

Description: Earthquake hypocentral location is perhaps the most classical problem in seismology, the solution of which is often affected by significant uncertainty. In monitoring the effects of underground anthropogenic activities, the earthquake hypocentral location, magnitude, and ground motions are important parameters for managing induced seismicity (as e.g., for operating traffic‐light systems). Such decisional systems define the operative reactions to be enacted once an earthquake, exceeding some magnitude or ground‐motion threshold, occurs within a monitoring volume defined in the neighborhood of a certain anthropogenic underground activity. In this case, a reliable evaluation of the hypocentral location, along with its uncertainty, becomes crucial for rational decision making. In this article, we analyze different sources of uncertainty that can be relevant for the determination of earthquake source locations, and introduce a logic‐tree‐based ensemble modeling approach for framing the problem in a decision‐making context. To demonstrate the performance of the proposed approach, we analyze uncertainties in the location of a seismic event that occurred on 22 July 2019 within the perimeter of the monitoring domain defined in the Val d’Agri oil field (southern Italy). We cast the result as a model ensemble that allows us to obtain samples from a parent distribution that better represents both aleatory and epistemic uncertainties of the earthquake location problem. We find that often‐neglected epistemic uncertainties (i.e., those that arise when considering alternative plausible modeling approaches or data) can be considerably larger and more representative of the state of knowledge about the source location, than the standard errors usually reported by the most common algorithms. Given the consequential repercussions of decision making under uncertainty, we stress that an objective evaluation of epistemic uncertainties associated with any parameter used to support decisional processes must be a priority for the scientific community.

Description: Centro per il Monitoraggio delle attività di Sottosuolo (CMS).

Description: Published

Description: 2423–2440

Description: 3SR TERREMOTI - Attività dei Centri

Description: JCR Journal

Description: Il Monte Amiata, ubicato nella porzione sud-occidentale della regione Toscana, è un edificio vulcanico che si è strutturato durante la parte finale del Pleistocene medio (350 - 200 ka; Laurenzi et al., 2015; Principe et al., 2018) al di sopra delle unità tettoniche strutturatesi durante le fasi mio-plioceniche dell’orogenesi appenninica. La distribuzione dei centri eruttivi sembra essere controllata da una zona di debolezza strutturale plio-pleistocenica, orientata circa NE-SW, che interessa sia i depositi vulcanici che le unità strutturali sottostanti (Brogi & Fabbrini, 2009, Brogi et al., 2015; Piccardi et al., 2017, Principe et al., 2018). Il gradiente geotermico è caratterizzato da valori molto alti (fino a 15°/100m), rendendo l’area particolarmente idonea per la produzione di energia geotermica. La produzione geotermica iniziò a partire dal 1960. Attualmente, gli impianti produttivi di ENEL- Greenpower di Bagnore e Piancastagnaio (Fig. 1), sfruttano un serbatoio geotermico collocato tra i 2000 e i 3500 metri di profondità rispetto al piano campagna. Il Catalogo Parametrico dei Terremoti Italiani (CPTI; Rovida et al., 2016 riporta, tra il 1287 e il 1940, 13 terremoti con una magnitudo equivalente compresa tra 4.5 £ Me £ 5.3 che hanno causato danneggiamenti fino al grado VIII MCS (Fig. 1), evidenziando un’attività sismica naturale e capace di causare seri danneggiamenti, ben prima dell’inizio dello sfruttamento geotermico dell’area. La sismicità recente, registrata dalla rete sismica nazionale dell’INGV (Castello et al., 2006; http://cnt.rm.ingv.it), riporta meno di 150 terremoti nell’area amiatina negli ultimi 25 anni, di cui 35 eventi con ML ≥ 1.5. Tra questi, il terremoto del 1.4.2000 (Md=4.0; http://cnt.rm.ingv.it/event/1132509) causò danni ad oltre 50 edifici, e la prossimità dell’epicentro con l’impianto di produzione di Piancastagnaio sollevò l’ipotesi di una sua natura antropogenica (Mucciarelli et al. 2001). Braun et al. (2018) hanno ricalcolato ipocentro e meccanismo focale di questo evento, collocandolo ad una profondità prossima al serbatoio di produzione, giungendo però alla conclusione che non sia possibile, per questa via, discriminare la sua natura antropogenica o meno. In generale, rispetto alle profondità tipiche della sismicità crostale osservata in Toscana (tra circa 5 e 13 km) gli ipocentri degli eventi sismici registrati nell’area amiatina hanno delle profondità simili a quelle di produzione (〈 5 km). La bassa densità della rete di monitoraggio INGV in quest’area del territorio nazionale (Fig. 1) è causa, comunque, di una bassa capacità di rilevazione (detection) sismica e di una altrettanto bassa capacità di risoluzione ipocentrale. Per migliorare le capacità di detection e di monitoraggio sismico nell’area del Monte Amiata, nel periodo 2015 - 2018 abbiamo installato una rete locale composta da 8 stazioni in vicinanza delle centrali di produzione geotermica di Bagnore e Piancastagnaio. L’obiettivo dell’esperimento era quello di abbassare la magnitudo di completezza e di comprendere meglio l’origine della sismicità in vicinanza degli impianti di estrazione, cercando di discriminare tra sismicità naturale e eventi sismici antropogenici. A questo scopo, abbiamo applicato una metodologia di analisi automatica, scansionando l’enorme dataset con un nuovo e robusto approccio di detection e localizzazione, chiamato waveform beam-forming grid search approach (LASSIE; Heimann et al., 2017). In uno step successivo, gli eventi sismici associati vengono rilocalizzati con un waveform-based locator (LOKI: Grigoli et al. 2014). Il catalogo sismico così ottenuto, aggiornato e molto più completo rispetto a quanto mai ottenuto prima in termini di Magnitudo di completezza (Mc), rappresenta la base per definire criteri di discriminazione, ad esempio attraverso la correlazione spazio-temporale della sismicità osservata con i parametri di produzione geotermica. I risultati ottenuti e le potenzialità di tale approccio saranno oggetto della presentazione qui proposta.

Description: Unpublished

Description: Roma

Description: 1TR. Georisorse

Description: On October 27, 2017, an Mw 4 earthquake occurred close to the municipality of Montesano sulla Marcellana, less than 10 km external to the concession of the largest European onshore hydrocarbon reservoir—the Val d’Agri oilfield (Southern Italy). Being a weak event located outside the extended monitoring domain of the industrial concession, the relevance of this earthquake and the possible links with the hydrocarbon exploitation were not extensively discussed. Actually, the analysis of shallow seismic events close to subsurface exploitation domains plays a significant role in the definition of key parameters in order to discriminate between natural, triggered, and induced seismicity, especially in tectonically active regions. The study of weak-to-moderate earthquakes can improve the characterization of the potentially destructive seismic hazard of this particular area, already struck by M 〉 6.5 episodes in the past. In this work, we analyze the source parameters of this Mw 4 earthquake by applying advanced seismological techniques to estimate the uncertainties derived from the moment tensor inversion and identify plausible directivity effects. The moment tensor is dominated by a NW–SE oriented normal faulting with a centroid depth of 14 km. A single ML 2.1 aftershock was recorded and used as the empirical Green’s function to calculate the apparent source time function for the mainshock. Apparent durations (in the range 0.11–0.21 s, obtained from S-waves) define an azimuthal pattern, which reveals an asymmetric bilateral rupture with 70% of the rupture propagation in the N310°Wdirection, suggesting a rupture plane dipping to the SW. Our results tally with the activation of a deeper fault segment associated with the Eastern Agri Fault System close to the basement as the origin of the Montesano earthquake. Finally, the Coulomb stress rate induced by depletion of the oilfield is calculated to quantify the trigger potential estimated for the Montesano earthquake yielding relatively low probabilities below 10%. Our analyses point toward the conclusion that the Mw 4 event was more likely due to the local natural tectonic stress, rather than induced or triggered by the long-term hydrocarbon extraction in the Val d’Agri oilfield.

Description: Published

Description: 617794

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal

Description: Mt. Amiata (Tuscany, Italy) is an extinct volcano whose last eruptive activity was dated about 200 ky ago. Today, its underlying crustal volume is still characterized by a high geothermal gradient, which makes the area particularly suitable for geothermal exploitation. Seismicity in the Tuscan Geothermal Areas is generally observed within the upper crust and is confined in depth by the so called K-horizon, a strong seismic reflector located in between 4-8 km b.s.l., often interpreted as the 400°C isotherme. The overlaying structure presents permeable layers of highly fractured volcanic rocks, saturated with hot water and steam. Geothermal exploitation from these layers started in the 1960's. Since then, shallow earthquakes have been occasionally observed close to the geothermal wells, and the question is whether these event are of natural origin or related to the exploitation of heat. To monitor the seismic activity inside the geothermal field of Mt. Amiata, we installed in 2015 a dedicated 8-station seismic network in the vicinity of the productive geothermal power plants for a 3-years recording period. The main challenges of our experiment are to automatically detect and locate the local microseismicity, trying to discriminate from natural seismicity those events caused by human operations. Due to the strong regional seismic activity of the 2016 Central Italy sequence, the automatic detection of local seismic events resulted challenging. We therefore use a waveform based detector (Lassie, developed at GFZ) to quickly scan the large dataset and automatically detect weak events in the target volume. Lassie provides preliminary event locations, which are then refined in a second step, using standard and waveform based techniques. For those hypocenters that are located close to the geothermal power plants, at a similar depth as the production level (3500 m b.s.l.), it remains very challenging to discriminate between natural and anthropogenic events.

Description: Published

Description: Seattle (WA)

Description: 4T. Sismicità dell'Italia

Description: In a joint project called OMEGA, between GFZ-Potsdam and the Istituto Nazionale di Geofisica e Vulcanologia (INGV), an experimental seismic monitoring system was installed in 2015 near the power plants of the geothermal area of Mt. Amiata (central Italy). The main objectives of this three-year experiment are: i) to monitor the seismic activity connected to any type of seismicity inside the geothermal field, ii) to verify if the low local seismicity rate near Mt. Amiata reported by the INGV bulletin is natural, or due to the sparse distribution of the INGV network, and iii) to discriminate natural from possibly induced seismicity. The eight-station network was extended by a sevenelement seismic array for the first four weeks. The aim of this paper is to present the first automatic hypocentre locations of the joint network/array analysis.

Description: Published

Description: 231-242

Description: 1TR. Georisorse

Description: JCR Journal

Description: The crustal volume beneath Mt. Amiata is characterized by a high geothermal gradient, which makes the area particularly suitable for geothermal exploitation. Seismicity in the Tuscan Geothermal Areas is generally observed within the upper crust and is confined in depth by the K-horizon, a strong seismic reflector located in between 4-8 km b.s.l., often interpreted as the 400°C isotherme. The overlaying structure presents permeable layers of highly fractured volcanic rocks, saturated with hot water and steam. Geothermal exploitation from these layers started in the 1960's. Since then, shallow earthquakes have been occasionally observed close to the geothermal wells, and the question is whether these event are of natural origin or related to the exploitation of heat. To monitor the seismic activity inside the geothermal field of Mt. Amiata, we installed in 2015 a dedicated 8-station seismic network in the vicinity of the productive geothermal power plants for a 3-years recording period. The main challenges of our experiment are to automatically detect and locate the local microseismicity, trying to discriminate from natural seismicity those events caused by human operations. We use a waveform based detector to quickly scan the large dataset and automatically detect weak events in the target volume, providing also preliminary event locations, which are then refined in a second step, using standard and waveform based techniques. For hypocenters located close to the geothermal power plants, at a similar depth as the production level (3500 m b.s.l.), it remains very challenging to discriminate between natural and anthropogenic events.

Description: Published

Description: Perugia

Description: 4T. Sismicità dell'Italia

Description: Most snow avalanches occur unobserved, which becomes particularly dramatic when human lives are involved. Seismological observations can be helpful to unravel time and dynamics of unseen events, like the deadly avalanche of January 18, 2017, that hit a Resort-hotel at Rigopiano in the Abruzzi (Italy). Particle motion analysis and spectrograms from data recorded by a close seismic broadband station, calculation of synthetic seismograms, as well as simulation of the flow, allowed us to construct the dynamics of the snow avalanche that buried alive 40 people, killing 29. Due to the bad weather conditions, no visual observation was made, thus making it impossible to determine the exact moment of the avalanche and to report necessary observations of the dramatic event. On-site inspections revealed that the hotel was horizontally cut by shear forces and dislocated by 48 m in 70°N direction, once the increasing avalanche pressure exceeded the structural shear strength of the building. Within an eligible 24 min time range of the avalanche, we found three weak seismic transients, starting at 15:42:38 UTC, recorded by the nearest operating station GIGS located in the Gran Sasso underground laboratory approximately 17 km away. Particle motion analysis of the strongest seismic avalanche signal, as well as of the synthetic seismograms match best when assuming a single force seismic source, attacking in direction of 120°N. Simulation of the avalanche dynamics-calculated by using a 2D rapid mass movement simulator-indicates that the seismic signals were rather generated as the avalanche flowed through a narrow and twisting canyon directly above the hotel. Once the avalanche enters the canyon it is travelling at maximum velocity (37 m/s) and is twice strongly deflected by the rock sidewalls. These impacts created a distinct linearly polarized seismic "avalanche transient"s that can be used to time the destruction of the hotel. Our results demonstrate that seismic recordings combined with simulations of mass movements are indispensable to remotely monitor snow avalanches. Seismology provides useful tools that can help to better understand the dynamics of seismic events, different from earthquakes, as e.g. volcanic eruptions, rock falls or huge landslides 1-5. There are only a few examples in literature where seismology was successfully used to study avalanches 6-10 , probably because the density of snow is up to ten times smaller, compared to debris, which results in a reduced ground coupling and in a smaller seismic signal amplitude. On January 18, 2017, in a remote location in the Abruzzo region (Central Italy), a deadly avalanche buried 40 people under the Resort-hotel "Rigopiano". In a dramatic rescue operation 11 people could be recovered, while for another 29 persons there was no way to escape. The bad weather conditions with heavy snowfall closed the access road, isolating the Rigopiano location from the outside world. The reduced visibility prevented any eyewitness report of the avalanche, thus the exact moment, as well as the dynamics of this catastrophic event, are still not confirmed. We use seismic recordings and on-site inspection, combined with numerical modelling, to reconstruct the dynamics and to determine the exact moment of the deadly avalanche.

Description: Published

Description: 18563

Description: 3T. Sorgente sismica

Description: JCR Journal

Description: Mt. Amiata is an extinct volcano whose last eruptive activity was dated about 200ky ago. Today, its underlying crustal volume is still characterized by a high geothermal gradient, which makes the area particularly suitable for geothermal exploitation. The structure overlaying the former magmatic reservoir is characterized by permeable layers of highly fractured volcanic rocks, saturated with hot water and steam. Geothermal exploitation from these layers started in the 1960's. Since then, earthquakes close to the depth of the geothermal production level at about 3.500 m depth occurred, shallower than the typical seismicity in the upper Tuscany crust. However, because of the sparse permanent monitoring network at Mt. Amiata, depth resolution and magnitude of completeness (Mc) have been poor. To improve the seismic monitoring inside the geothermal field of Mt. Amiata, we installed in 2015 for a 3-years recording period a dedicated 8-station seismic network in the vicinity of the productive geothermal power plants. The aim of the experiment was achieve smaller completeness magnitude Mc and to reduce depth uncertainty, in order to better understand the seismicity and to be able to discriminate between natural and anthropogenic events. We scan the large dataset using an efficient waveform beam-forming grid search approach (LASSIE) for robust detection and rough locations. In a second processing step associated earthquakes are re-located by a refined waveform-based locator (LOKI). Obtaining an improved seismic catalog with reduced Mc, we suggest to approach the discrimination problem by spatial-temporal correlation of seismicity with geotechnical time-series of geothermal production.

Description: Unpublished

Description: Montreal (CA)

Description: 1TR. Georisorse

Description: During the last decades, seismic monitoring experienced important advances by introducing small aperture arrays and dense seismic networks equipped with high-dynamic-range instrumentation. This new recording reality allowed to lower significantly the monitoring threshold, to identify in quasi real time active seismo-tectonic structures and to reveal information about the seismic source and its rupture dynamics. The application of array techniques, as beamforming and f-k analysis use the coherence properties of the recorded wavefield for increasing the S/N-ratio, to determine back-azimuth and apparent velocity of the incoming wavefield and to automatically locate the seismic events of small magnitudes. We realized the first permanent small aperture array installation in Italy, called CISA (Central Italy Seismic Array) composed of 9 three-component seismic sensors installed at interstation distances from 100 - 500 m and a maximal extension of 1000 m. CISA's circular configuration and its geographical position is aimed to monitor the microseismicity of Central Italy at a local and regional range, including the epicentral area of the 2016/17 seismic sequence, as well as the geothermal areas in the western sector. CISA's challenges are to decrease the detection threshold of the microseismicity, to identify active faults in Umbria by analysis of the microseismicity and to study in detail the rupture dynamics of moderate earthquakes, by using source scan algorithm.Seismic data are transmitted in real-time to the data center of SARA-electronic (Perugia) by ordinary 4G-LTE router and then forwarded to the observatories of Arezzo and Munich by using seedlink protocol. An ObsPy module manages the fk-detection, calculating in real-time backazimuth, slowness, gain and semblance. On a local scale CISA is expected to operate in a magnitude range from 0〈M〈3, which could be easily extended to 3〈M〈6 by installing additional accelerometers.

Description: Published

Description: 1051

Description: Perugia

Description: 4T. Sismicità dell'Italia

Description: JCR Journal