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Seismic Monitoring of an Underground Natural Gas Storage Facility: The Collalto Seismic Network
Abstract
The Collalto Seismic Network (Rete Sismica di Collalto, or RSC) is the infrastructure used to monitor
the natural and induced seismicity of the natural gas storage concession known as Collalto Stoccaggio,
which is located in northeastern Italy. This network was realized and is currently managed by the
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), a public research institute, on
behalf of Edison Stoccaggio S.p.A., the storage concession holder.
In our article, we describe the seismic network and the results obtained in the first two years of
monitoring, from 1 January 2012 to 31 December 2013.
Online Material: Seismic-hazard map, figures of event location and waveforms, phase reading distribution, and background seismic noise; and tables of event parameters, 1D regional model, and earthquake catalog.
This copy is for distribution only by the authors of the article and their institutions in accordance with the Open Access Policy of the Seismological Society of America. For more information see the publications section of the SSA website at www.seismosoc.org ○ E
Supplementary resource (1)
... The RSC is a local network that thickens the regional one (Sistema di Monitoraggio terrestre dell'Italia Nord Orientale -SMINO; Bragato et al. 2011Bragato et al. , 2021, and it is composed of 10 stations (Priolo et al. 2015a) used for monitoring the microseismicity potentially induced by an underground gas storage since 2012. The Peruzza et al. (2022b): a 1 ) map of the stations used in this work, red triangles belong to the SMINO network (Bragato et al. 2021), white ones to the local Collalto Seismic Network (RSC, Priolo et al. 2015a), color frames indicate respectively the plot area represented in a 2 (black), the target area of the RSC (orange) and the Refrontolo area (near Pieve di Soligo) involved by the unusually productive sequence analyzed (green); a 2 ) epicentral map with main tectonic element taken from Burrato et al. (2008): MT indicates the Montello thrust: the epicenters symbol size is proportional to local magnitude M L , depth is color-coded according to scale bar (bottom right) for the events occurred in August, transparent circles show the location of the seismicity detected from 2012 in the region; the black area with purple contour shows the surface projection of the Collalto underground gas storage (UGS); a 3 ) histogram of the daily number of events manually located by the RSC network in August 2021, referred to the Refrontolo sequence (orange) or to other locations. ...
... The RSC is a local network that thickens the regional one (Sistema di Monitoraggio terrestre dell'Italia Nord Orientale -SMINO; Bragato et al. 2011Bragato et al. , 2021, and it is composed of 10 stations (Priolo et al. 2015a) used for monitoring the microseismicity potentially induced by an underground gas storage since 2012. The Peruzza et al. (2022b): a 1 ) map of the stations used in this work, red triangles belong to the SMINO network (Bragato et al. 2021), white ones to the local Collalto Seismic Network (RSC, Priolo et al. 2015a), color frames indicate respectively the plot area represented in a 2 (black), the target area of the RSC (orange) and the Refrontolo area (near Pieve di Soligo) involved by the unusually productive sequence analyzed (green); a 2 ) epicentral map with main tectonic element taken from Burrato et al. (2008): MT indicates the Montello thrust: the epicenters symbol size is proportional to local magnitude M L , depth is color-coded according to scale bar (bottom right) for the events occurred in August, transparent circles show the location of the seismicity detected from 2012 in the region; the black area with purple contour shows the surface projection of the Collalto underground gas storage (UGS); a 3 ) histogram of the daily number of events manually located by the RSC network in August 2021, referred to the Refrontolo sequence (orange) or to other locations. b) LOC-FLOW processing configuration used in this study (modified from Zhang et al. 2022). ...
... To date, no earthquakes have been associated with methane storage activities; conversely, natural microseismicity has yielded exceptional 3D imaging of the Montello thrust (Moratto et al. 2019;Romano et al. 2019;Picotti et al. 2022), a resource not available when Galadini et al. (2005) hypothesized the existence of a single fault segment capable of M 6.7 earthquakes with an average recurrence interval of about 700 years. RSC real-time seismic monitoring is performed with a customized workflow of the BRTT Antelope routines (Garbin and Priolo 2013;Moratto and Sandron 2015;Priolo et al. 2015a): automatic earthquake detection is based on STA/LTA algorithms, gridsearch location uses the IASPEI global velocity models and multiscale sized grids to discriminate local, regional and teleseismic events, and local magnitude is estimated. Alert conditions are set to activate an immediate manual refinement of location and magnitude estimation by the seismologist on-call. ...
It is an open question whether machine-learning (ML) methods can be trusted in areas where dense and localized seismic networks are in operation, and prompt and accurate detection and location of earthquakes are essential to guide decision-making processes that contribute to seismic-risk-mitigation-strategies, even for very low-magnitude events. To address these concerns, we compare the performance of a widely-used ML phase picker, PhaseNet, integrated with several popular earthquake location methods (included in LOC-FLOW), with the results obtained by the workflow adopted since 2012 by the Collalto Seismic Network, installed to monitor natural and potentially induced microearthquakes nearby an underground gas storage. The tested dataset concerns the most populated microseismic sequence observed so far (374 events, ML⩽2.5, August 2021, Refrontolo, NE-Italy), as its unusual productivity raised some criticalities in the combination of automatic routines, and time-consuming manual revision of phase picks adopted by the standard workflow. LOC-FLOW is able to detect the majority of the events listed in the manually revised catalog, demonstrating its ability to efficiently and accurately build earthquake catalogs from continuous seismic data. We highlight both the advantages and limitations of the ML-picker and recommend the use of template-matching-techniques in the final stage of processing to increase the number of events.
... Some moderate earthquakes occurred in the second half of XIX century, and, since 1977, few 3 < M < 4 events ( Figure 3a) have been recorded by the regional seismic network and by temporary monitoring (see Sugan & Peruzza, 2011 and references therein). The quality of the instrumental catalogs is non-uniform in time and space (Danesi et al., 2015; see Romano et al., 2019, and revised catalogs cited therein), till when, in 2011, a local dense network has been deployed to microseismically monitor the Collalto underground gas storage (Priolo et al., 2015). ...
... We will address this point in Sections 6 and 7 of this paper. After the depletion of the Conegliano gas field, the reservoir was turned into an Underground Gas Storage, named Collalto Storage, still operating, and microseismically monitored since 2012 (Priolo et al., 2015;Romano et al., 2019). Based on this monitoring, we present a reconstruction of the rock volume affected by microseismicity, providing constraints for the construction of the cross-sections (Section 5). ...
... This network has been designed and is still managed by OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) on behalf of Edison Stoccaggio S.p.A., to monitor the seismicity potentially induced by gas storage activities in the Collalto reservoir. RSC is a high-resolution permanent network, consisting of a cluster of high-sensitivity stations deployed right above the reservoir, fully operating since 2012 (Priolo et al., 2015). Over the years, RSC has provided a detailed picture of the Montello area background seismicity, so far poorly known, and has demonstrated that the underground storage activities are not related to such microseismic events (Peruzza et al., 2022;Romano et al., 2019). ...
Plain Language Summary
The definition of the hazard in a seismically active area, such as the front of a mountain chain, requires a precise reconstruction of the geometry of the tectonic structures. In the densely populated foothills of the eastern Southern Alps of Italy, these structures do not reach the surface and are difficult to study. Combining surface and subsurface data with precisely located microseismicity, we provide a synthetic view on the geometry and evolution of the active mountain front. We find that the frontal structure is larger and deeper than previously thought, and it reaches the outskirts of one of the main cities of the area, Treviso. The tectonic stratigraphy of the area, and the geomorphology of a gentle fold (Montello anticline), reveal that the structure (Montello thrust [MT]) is much older, therefore its rates of deformation much lower, than previously thought. Most of the active deformation is focused in a northern structure, named Bassano‐Valdobbiadene thrust. Together, these structures account for the Adria‐Europe convergence, as defined by geodetic velocity field. Their behavior as thrust system is complex, with locked patches and freely slipping portions, such as the MT and would require a future modeling of their interactions.
... The Montello-Conegliano thrust is part of the active, compressive external front of the eastern Southern Alps and it is bounded by the Bassano-Cornuda thrust to E, the Cansiglio thrust to NE, the Bassano-Valdobbiadene to N, and the Arcade thrust to S ( Figure 1) [8,31]. The activity of these structures is testified by geological, geodetic, and seismological studies showing a compression rate of 1-2 mm/yr [33], according to N-S or NNW-SSE convergence and a low magnitude (M < 4) instrumental seismicity [6,8]. The active thrusts are kinematically independent and are rooted in the mid-crust (15-20 km) as evidenced by seismic profiles and seismicity [29]. ...
... The Collalto underground gas storage is shown in grey with the internal (two grey lines) and extended domain (three grey lines) areas. The monitoring areas A and B according to [6] are highlighted with dashed red lines. Historical seismicity with epicentral macroseismic intensity I0 > 4 is reported (CPT15, [34]). ...
... [8], to show that the seismicity depicts the Montello-Conegliano active thrust as a gently NE-dipping plane, locally interrupted by minor faults, with earthquakes located at 5-13 km depth. In 6 years (2012-2017), [8] analysed 1635 earthquakes with −0.8 ≤ ML ≤ 4.5 with strongest events located northeastward, outside the principal monitored region, in a 20 km wide square area denoted as the area A in [6] (see the smallest red dashed square in Figure 1). The largest events are spatio-temporally clustered in seismic sequences that occurred near Sedico-Belluno, Vidor-Valdobbiadene, Cavaso del Tomba-Segusino (with 3.3 < Mmax < 3.8), and in the Pieve di Soligo, Tarzo-Vittorio Veneto and Alpago areas (with 2.0 < Mmax < 3.0; Figure 1). ...
Seismic monitoring in areas where induced earthquakes could occur is a challenging topic for seismologists due to the generally very low signal to noise ratio. Therefore, the seismological community is devoting several efforts to the development of high-quality networks around the areas where fluid injection and storage and geothermal activities take place, also following the national induced seismicity monitoring guidelines. The use of advanced data mining strategies, such as template matching filters, auto-similarity search, and deep-learning approaches, has recently further fostered such monitoring, enhancing the seismic catalogs and lowering the magnitude of completeness of these areas. In this framework, we carried out an experiment where a small-aperture seismic array was installed within the dense seismic network used for monitoring the gas reservoir of Collalto, in North Italy. The continuous velocimetric data, acquired for 25 days, were analysed through the application of the optimized auto-similarity search technique FAST. The array was conceived as a cost-effective network, aimed at integrating, right above the gas storage site, the permanent high-resolution Collalto Seismic Network. The analysis allowed to detect micro-events down to magnitude Ml = −0.4 within a distance of ~15 km from the array. Our results confirmed that the system based on the array installation and the FAST data analysis might contribute to lowering the magnitude of completeness around the site of about 0.7 units.
... The Montello-Conegliano thrust is part of the active, compressive external front of the eastern Southern Alps and it is bounded by the Bassano-Cornuda thrust to E, the Cansiglio thrust to NE, the Bassano-Valdobbiadene to N, and the Arcade thrust to S ( Figure 1) [8,31]. The activity of these structures is testified by geological, geodetic, and seismological studies showing a compression rate of 1-2 mm/yr [33], according to N-S or NNW-SSE convergence and a low magnitude (M < 4) instrumental seismicity [6,8]. The active thrusts are kinematically independent and are rooted in the mid-crust (15-20 km) as evidenced by seismic profiles and seismicity [29]. ...
... The Collalto underground gas storage is shown in grey with the internal (two grey lines) and extended domain (three grey lines) areas. The monitoring areas A and B according to [6] are highlighted with dashed red lines. Historical seismicity with epicentral macroseismic intensity I0 > 4 is reported (CPT15, [34]). ...
... [8], to show that the seismicity depicts the Montello-Conegliano active thrust as a gently NE-dipping plane, locally interrupted by minor faults, with earthquakes located at 5-13 km depth. In 6 years (2012-2017), [8] analysed 1635 earthquakes with −0.8 ≤ ML ≤ 4.5 with strongest events located northeastward, outside the principal monitored region, in a 20 km wide square area denoted as the area A in [6] (see the smallest red dashed square in Figure 1). The largest events are spatio-temporally clustered in seismic sequences that occurred near Sedico-Belluno, Vidor-Valdobbiadene, Cavaso del Tomba-Segusino (with 3.3 < Mmax < 3.8), and in the Pieve di Soligo, Tarzo-Vittorio Veneto and Alpago areas (with 2.0 < Mmax < 3.0; Figure 1). ...
Seismic monitoring in areas where induced earthquakes could occur is a challenging topic for seismologists due to generally very low signal to noise ratio. Therefore, the seismological com-munity is devoting several efforts to the development of high-quality networks around the areas where fluid injection and storage and geothermal activities take place, also following the national induced seismicity monitoring guidelines. The use of advanced data-mining strategy, such as template matching filters, auto-similarity search and deep-learning approaches is recently further fostering such a monitoring enhancing the seismic catalogues and lowering the magnitude of completeness of these areas. In this framework, we carried out an experiment where a small-aperture seismic array was installed around the gas reservoir of Collalto, in North Italy. The continuous velocimetric data, acquired for 25 days, were analysed through the application of the optimized auto-similarity search technique FAST. The array was conceived as a cost-effective network, aimed at integrating, right above the gas storage site, the permanent high-resolution Collalto Seismic Network. The analysis allowed to detect micro-events down to magnitude Ml=-0.4 within a distance of ~15km from the array. Our results confirmed that the system based on the array installation and the FAST data-analysis might contribute to lower the magnitude of completeness around the site of about 0.7.
... Next, we apply the procedure to synthetic waveforms in order to evaluate its robustness and performance. Finally, we describe two real case applications, corresponding to two swarms of low-magnitude earthquakes recorded in the area monitored by the Collalto Seismic Network (northeast Italy, see Fig. 1; Priolo et al. 2015;Moratto et al. 2019). First, we use the manual picks and locations (www.rete-collalto.crs.inogs.it) of the first swarm to finely tune our method; then, we apply our method to the second swarm, and compare the automatic detections and locations with those obtained manually by the monitoring operators (www.rete-collalto.crs.inogs.it). ...
... First, we tune the procedure on the ideal noisefree and exact velocity model case, then we investigate the effects of noise in the waveforms and the adoption of an incorrect velocity model. We compute the seismograms with the wavenumber integration method (Herrmann 2013) for the horizontally layered medium listed in Table 1 (Model 1) and consider the receiver locations corresponding to 10 three-component seismic stations resembling the existing Collalto Seismic Network (Fig. 1), that is, the seismic monitoring infrastructure of the natural, underground gas storage located in Collalto, at the foothills of Southern Alps, in northeastern Italy (Priolo et al. 2015). We compute synthetic seismograms for a strike slip point source at depth = 1.0 km, with moment magnitude M w = 2.0. ...
... We test MigraLoc on two seismic swarms recorded by the Collalto Seismic Network (Priolo et al. 2015;Moratto et al. 2019), hereafter called RSC according to its Italian name (Fig. 1). The RSC is the infrastructure used to monitor the natural and induced seismicity of the natural gas storage concession known as Collalto Stoccaggio. ...
Prompt detection and accurate location of microseismic events are of great importance in seismic monitoring at local scale and become essential steps in monitoring underground activities, such as oil and gas production, geothermal exploitation and underground gas storage, for implementing effective control procedures to limit the induced seismicity hazard. In this study, we describe an automatic and robust earthquake detection and location procedure that exploits high-performance computing and allows the analysis of microseismic events in near real-time using the full waveforms recorded by a local seismic network. The implemented technique, called MigraLoc, is based on the space–time migration of continuous waveform data and consists of the following steps: (1) enhancement of P and S arrivals in noisy signals through a characteristic function, by means of the time–frequency analysis of the seismic records; (2) blind event location based on delay-and-sum approach systematically scanning the volume of potential hypocentres; (3) detection notification according to the information content of the hypocentre probability distribution obtained in the previous step. The technique implies that theoretical arrival times are pre-calculated for each station and all potential hypocentres as a solution of the seismic-ray equation in a given 3-D medium. As a test case, we apply MigraLoc to two, low-magnitude, earthquake swarms recorded by the Collalto Seismic Network in the area of the Veneto Alpine foothills (Italy) in 2014 and 2017, respectively. Thanks to MigraLoc, we can increase the number of events reported in the network catalogue by more than 25 per cent. The automatically determined locations prove to be consistent with, and overall more accurate than, those obtained by classical methods using manual time-arrival picks. The proposed method works preferably with dense networks that provide signals with some degree of coherency. It shows the following advantages compared to other classical location methods: it works on the continuous stream of data as well as on selected intervals of waveforms; it detects more microevents owing to the increased signal-to-noise ratio of the stacked signal that feeds the characteristic function; it works with any complex 3-D model with no additional effort; it is completely automatic, once calibrated, and it does not need any manual picking.
... Since the end of the first decade of the 2000 years, the National Institute of Oceanography and Applied Geophysics (OGS) has been in charge of the seismic monitoring of the underground gas storage (UGS) activity managed by Edison Stoccaggio S.p.A. at Collalto, a small locality of Northeastern Italy ( Fig. 1; Priolo et al. 2015). A dedicated seismic monitoring infrastructure, the Collalto Seismic Network (Rete Sismica di Collalto, RSC), was realized and is fully operating since January 1, 2012. ...
... The reservoir extends approximately over a 10 km × 4 km area at 1500-1600 m of depth. The UGS activity started in 1994 and operates in a traditional way, i.e., the gas is injected into the reservoir during the warm season and is extracted from it during the cold one (Priolo et al. 2015). For more than 15 years, the gas storage pressure has been held within approximately the 80% of the pressure at which the gas was found within the reservoir (~160 bar). ...
... All detections are reviewed at a second time by a seismologist; at this level, all seismic events are validated and relocalized manually. More details can be found in Priolo et al. (2015) and Romano et al. (2019). ...
Underground fluid injection and extraction is able to change pore fluid pressure at depth and make faults unstable, due to friction-force reduction, with an increased possibility of triggering earthquakes. Studying the local seismicity, down to microearthquakes, and stress field in areas where such activities are developed are essential steps to discriminate between natural and induced events. In this context, the moment magnitude (Mw) is a key-parameter to both evaluate the energy balance and the stress involved in earthquake rupture process and assess seismic hazard accurately. Here, we focus on the fast Mw estimation of microearthquakes recorded around the underground gas storage of Collalto (Northeastern Italy) by a dedicated seismic monitoring network. The area of Montello-Collalto, where this industrial activity is carried out, is densely populated and characterized by relevant seismic hazard. We compute Mw from the response spectra (SA) calculated at fixed periods (i.e., 1.0 and 0.3 s); we show that log (SA) and Mw scale as 2/3 and extend our method to microseismicity by using response spectra at 0.1 s. We eventually estimate Mw for 1659 events (0.4 ≤ Mw ≤ 3.5) and find that ML and MW scale as 2/3 too. The discrepancy between these two magnitude scales affects both the Gutenberg-Richter parameters and completeness magnitude estimations; therefore, it has consequences when those quantities are used for physical interpretation. Our procedure shows to be efficient and suitable to be implemented within standard routine analyses of real-time monitoring and feed decision-making processes about plant management, such as the traffic light protocols.
... In 1994, Edison Stoccaggio Spa started to use the Collalto natural reservoir as UGS by injecting natural gas during the warm season and withdrawing it during the winter according to protocols stated by the Italian Ministry of the Economic Development (MiSE), which handles this type of strategic resource. At the end of 2011, to accomplish the request of increasing the storage capabilities by reaching the original gas pressure of the reservoir (∼160 bars), a high-sensitivity seismometric network named the Collalto Seismic Network (in Italian, Rete Sismica di Collalto [RSC]) was deployed around this UGS plant; the network geometry is dense above the reservoir with an interstation distance of ∼2-4 km (Priolo et al., 2015). The main goal of the RSC is to monitor the microseismicity potentially induced by the storage activities. ...
... The Collalto Seismic Network (RSC) is a cluster of 10 stations deployed to detect and locate potentially induced microearthquakes (M w ≤ 2) occurring in or near the Collalto UGS ( Fig. 2), as well as the natural tectonic earthquakes associated with the active faults existing in the surroundings. The RSC stations are equipped with high-sensitivity and high-dynamic sensors, that is, pairs of velocimeters and accelerometers (Priolo et al., 2015). About 9 of 10 stations are equipped with 10 or 30 s natural period borehole seismometers, and one has a broadband seismometer with a 120 s natural period. ...
... Digital data are continuously radio transmitted from the stations to the main acquisition center with 200 and 100 Hz sampling for the velocimeters and accelerometers, respectively, and archived in miniSEED format on a network storage server. Four computers, each equipped with a Ring Server (see Data and Resources), acquire continuous waveforms from the stations of the RSC and the other networks the RSC is integrated with (details in Priolo et al., 2015); two computers automatically process and analyze real-time data and another is devoted to offline processing. The RSC has been fully operational in monitoring the Collalto UGS activity since 1 January 2012 and acquires ∼1 GB per day of continuous recordings. ...
... In line with such recommendations, the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale -OGS has designed a highsensitivity network with the aim of monitoring the underground gas storage (UGS) activity carried out in the depleted gas reservoir of Collalto (Northeastern Italy) and providing highly accurate locations of the seismicity occurring near the reservoir (Priolo et al., 2015a). The area under study is located in the foothills of the Southeastern Alps, close to seismogenic faults capable of generating strong earthquakes (M W ≥ 6) (e.g., Burrato et al., 2008). ...
... The reservoir is a depleted natural gas deposit, approximately 8 km long and 1.5 km wide, managed according to seasonal cycles of gas extraction during the winter, and gas injection during the summer at a pressure of 160 bars close to the original pressure. Since 2012, the seismicity around the reservoir has been monitored by the Collalto Seismic Network (OGS, 2012) -international code EV; EV network hereinafter-which is composed of 10 stations (Priolo et al., 2015a) mainly located on Plio-Pleistocene clays (Avigliano et al., 2008) at the northern margin of the Venetian Plain (Fig. 1a). Nine stations are equipped with borehole seismometers with extended period (T = 10 s or T = 30 s) and one with a broad-band seismometer (T = 120 s), in continuous data acquisition at 200 Hz. ...
... contributed to its location (Table 1), 40 s of pre-event ambient noise included; when the S-wave arrival time is not picked, a theoretical value is estimated on the basis of the P-wave arrival time, earthquake location and V P /V S = 1.77 (Priolo et al., 2015a). Furthermore, to avoid possible P-and S-wave contamination by secondary wave arrivals (e.g., the Moho reflections observed by Bragato et al., 2011), we limit our analysis to the signals recorded at hypocentral distances within 80 km. ...
The study of seismic source parameters is crucial for understanding the origin of seismicity and retrieving information on the energy balance and the stress involved in earthquake rupture processes. In active tectonic areas, where underground industrial activities are carried out, such parameters may help to understand whether earthquakes are induced, triggered, or natural. The Montello-Collalto area (Southeastern Alps) is located in an active tectonic environment and hosts a depleted natural reservoir used to store gas. Since 2012, a high-quality seismic network monitors the microseismicity occurring around the underground gas storage reservoir to understand if the storage activity might induce seismicity. In this paper, we estimate the source parameters of low magnitude events representative of the seismicity occurring in the area surrounding the reservoir. The analysis
includes a preliminary removal of the site effects, specifically computed within this study, from all the records. Then, using a parametric multistep inversion scheme, we estimate the seismic moment, the corner frequency and the static stress drop, that can be set as reference for the microseismicity occurring in the study area. All the investigated earthquakes show low seismic efficiency compatible with overshoot processes, which is typical of natural (i.e., tectonic) earthquakes. Our procedure can be implemented in other tectonic regions hosting underground industrial activities to support the decisional processes related to real-time monitoring.
... In the Netherlands, for example, in addition to the previously reported case of UGS in Bergemeer, a large microseismic network with more than 60 borehole stations has been set up to monitor the industrial activities of gas production in the Groeningen field. In Italy, the Collalto UGS site (northern Italy) is monitored by a dedicated microseismic network (Priolo et al., 2015) consisting of 10 stations equipped with borehole seismometers. Another experience of gas storage monitoring in Italy is that conducted in the depleted gas field of Minerbio, where the local microseismic network consists of 8 stations, 4 of which are equipped with borehole sensors at a depth of 100-150 m (Carannante et al., 2020(Carannante et al., , 2021. ...
... supplemented by some procedures and functions developed by OGS staff. The monitoring system has both real-time and off-line data processing and uses similar procedures to those adopted by OGS for monitoring the Collalto UGS, as described in Priolo et al. (2015). ...
Plain Language Summary
Just as power banks store energy or artificial lakes store water for later use, depleted hydrocarbon reservoirs are used to store gas for later exploitation. Underground gas storage (UGS) is needed to optimize the distribution system and balance near‐constant production/distribution flows with variable market demand. It also ensures gas supply in exceptional situations such as geopolitical instability or severe winters. Since UGS activities (essentially warm season gas injection and cold season gas extraction) interact with surrounding geological structures, geophysical monitoring is recommended. This article describes the new monitoring infrastructure established at the Cornegliano Stoccaggio UGS (Po Valley, Italy) and the results of 5 years of seismic and ground deformation measurements. The monitoring began 2 years before the start of UGS activities and covers the first 3 years of gas storage, allowing us to observe the phenomena associated with the “birth” of a UGS with remarkable observational capabilities. Our study confirms that UGS in depleted gas reservoirs, if well managed, can result in negligible, if any, human‐induced seismicity and limited ground surface deformation. It also demonstrates the importance of measuring undisturbed conditions prior to industrial activities for a sufficiently long period of time, to properly interpret the phenomena observed later.
... The RSC has been fully operational since 2012; it was developed and is managed by OGS on behalf of Edison Stoccaggio S.p.A. The 10 RSC stations (white triangles in Figure 1) are equipped with extended-band borehole seismometers (with natural period T ≥ 10 s), and integrated by other stations of the regional network managed by OGS (for further details see Priolo et al., 2015). The RSC stations and network geometry, the detection and location procedures have no notable differences since the installation, thus providing a precious dataset of observations lasting more than 10 years (RSC catalog, see Data Availability Section); within the best earthquake detectability area (Area A in Figure 1, about 20 km wide), magnitude completeness can be considered uniform in time and space and is close to M L 0.0 since 2012 . ...
... Meanwhile, several more events (black circles in Figure 2B) occurred in the area of Lake Alpago and S. Croce, about 25 km northeast of Refrontolo (with maximum magnitude M L 2.3 on 3 August at 6:52:49, near Pieve D'Alpago in Figure 1); thereafter, activity continued near Valdobbiadene. Despite the unusual number of events, automatic real-time earthquake detection and localization based on the STA/LTA trigger algorithm and association by grid search of the Antelope software package were followed by manual offline reading of pickings, earthquake relocation, and local magnitude estimation according to our standard data processing (Priolo et al., 2015;Romano et al., 2019). Routine relocations use Hypo71 (Lee and Lahr, 1975; hereafter H71) with a regional 1D velocity model and fixed V P /V S = 1.78 (obtained from the modified Wadati diagram based on the entire data set), and Hypoellipse (Lahr, 1999;HEL) with a local, more detailed 1D velocity model with V P /V S , which varies in depth (velocity model and stations corrections given in the Supplementary Material; Supplementary Tables S2, S3). ...
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 following considerable public alarm lead the Italian government to halt releasing new hydrocarbon leases and to deliver new guidelines for monitoring the seismicity in areas surrounding subsurface industrial activities (MiSE 2014; i.e., "Guidelines for monitoring the seismicity in industrial activities", hereinafter, MISE-GL). For instance, in line with such recommendations, a high-sensitivity network was designed by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) for monitoring the Collalto underground gas storage (UGS) activity carried out in northeastern Italy (Priolo et al. 2015;Moratto et al. 2019). ...
... For the sake of simplicity, we considered a scenario with a symmetrical reservoir shape and regular network layout. Of course, in real cases, the constrains given by the reservoir geometry and by topographic/ logistic issues can lead to designing different network geometries but with the same monitoring performances (for instance, as in the case of the Collalto Network; Priolo et al. 2015). We studied the performance of different network configurations covering an area of about 30 km by 30 km around a wastewater reinjection well. ...
The continuous monitoring of the spacetimemagnitude evolution of seismicity is a crucial task to assess the geomechanical conditions of hydrocarbon reservoirs. It is fundamental to design optimized high sensitivity and cost effective seismic networks able to detect and locate low magnitude events with high accuracy. In Italy, after the concern for the 2012 Emilia earthquake, the government released the guidelines for monitoring the seismicity in areas surrounding subsurface industrial activities. In this work we propose an optimization study for seismic monitoring networks based on the guideline requirements. We evaluated
the performance, in terms of detection/location thresholds and events location errors, of different network layouts constructed by varying the station density and geometry and considering also the integration of seismic arrays. We simulated sets of seismic sources at different depths by varying magnitude and stress drop values. We considered two different values of noise level at the stations. The results show that the station density and the noise level represent the crucial parameters for the seismic network performances.
The performances of a standard network comply the guidelines requirements in term of detection/location thresholds. Only the integration of seismic networks with arrays allows to decrease the location errors of several hundreds of meters to reach the required location accuracy. So, the integration of standard network with seismic arrays allows to achieve the network performance standard in terms of detection capability and location accuracy and, in some cases, to improve it.
... The epicentral area of these earthquakes is very close to the natural gas storage reservoir of Collalto, which is being monitored by a dedicated microseismic network [Priolo et al., 2015]. While the national network located only six events with uncertainties of few kilometers (http://iside.rm.ingv.it), the NE Italy regional network managed by the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS) located about 90 events with uncertainties generally below 1 km. ...
... Although this situation seems quite common in the U.S. [Hornbach et al., 2015], where most of the industrial sites do not have a dedicated microseismic network, monitoring conditions in Europe are often poor. Except few cases worth of note, like Groningen (Netherlands, see the previous sections), Collalto (Italy [Priolo et al., 2015]), Basel (Switzerland [Kraft and Deichmann, 2014]), and St. Gallen ((Switzerland [Edwards et al., 2015]), where the presence of dedicated networks, equipped with different instrument types including broadband seismic stations, borehole sensors, and accelerometers, guarantee optimal monitoring conditions, many industrial sites still lack appropriate monitoring infrastructure. For instance, Blackpool (UK [Clarke et al., 2014]) and Castor (Spain [Cesca et al., 2014;Gaite et al., 2016]) seismicity cases are among the most scrutinized induced seismicity cases in Europe, where the lack of an adequate monitoring network did not allow a quick and accurate analysis of the microseismicity. ...
Due to the deep socioeconomic implications, induced seismicity is a timely and increasingly relevant topic of interest for the general public. Cases of induced seismicity have a global distribution and involve a large number of industrial operations, with many documented cases from as far back to the beginning of the 20th century. However, the sparse and fragmented documentation available makes difficult to have a clear picture on our understanding of the physical phenomenon and consequently in our ability to mitigate the risk associated with induced seismicity. This review presents a unified and concise summary of the still open questions related to monitoring, discrimination and management of induced seismicity in the European context and, when possible, provides potential answers. We further discuss selected critical European cases of induced seismicity, which led to the suspension or reduction of the related industrial activities.
... Introduzione. Dal 2012 OGS è impegnato nel monitoraggio e nello studio della microsismicità eventualmente indotta dalle attività di stoccaggio di gas metano nella concessione di Collalto (Treviso), oltre che della sismicità naturale nell'area circostante (Priolo et al., 2015a). In un simile contesto, una stima affidabile della magnitudo momento (M w ) associata agli altri parametri di sorgente per gli eventi locali, anche se molto piccoli, diventa essenziale per l'analisi dei meccanismi di sorgente e la discriminazione tra terremoti indotti e terremoti di origine naturale. ...
... ed elaborati sia in real-time che offline. Il processing standard dei dati prevede: 1) identificazione automatica degli eventi, ossia di aumenti di ampiezza del segnale sincroni su più stazioni; 2) riconoscimento e picking manuale dei terremoti locali; 3) localizzazione e stima della magnitudo locale (Priolo et al., 2015a). ...
... The two insets provide the geographical framework of the study area; the inset to the left also shows the locations of the regional stations that enter into the RSC system. More details can be found in Priolo, Romanelli, et al. (2015). cross correlation to estimate the angle of alignment among OBSs in the Aegean Sea and inland stations, whereas Zha and Menke (2013) developed a method for determining the horizontal orientation of OBSs by analyzing the polarization of Rayleigh waves retrieved from ambient-noise cross correlation. ...
... It extends approximately over a 10 km × 4 km area (Fig. 1). Full details about the overall framework in which the RSC operates, as well as its technical features, are described in Priolo, Romanelli, et al. (2015), whereas a synthesis of the most important pieces of information for what concerns this study is reported hereafter. ...
One of the most critical problems affecting seismological data acquisition is related to possible misorientation of three-component seismic sensors. This generally happens when their orientation cannot be measured directly, as in the case of sensors deployed in boreholes. We describe here the sensor reorientation procedure of the Collalto Seismic Network, a microseismic monitoring network located in northeastern Italy that consists of 10 broadband three-component stations deployed in boreholes. We apply a procedure based on the misfit minimization of a complex trace recorded by a given station with respect to a reference station for which orientation is known. The main advantage of this methodology is that the reorientation of seismic sensors can be viewed as a linear inverse problem in the complex domain, which ensures that the preferred solution corresponds to the global minimum of a misfit function. Furthermore, it is also possible to simultaneously use more than one seismic event to better constrain the solution of the inverse problem. In this article, we further compare the orientation results obtained for a seismometer-seismometer sensor pair with those obtained using an accelerometer-seismometer sensor pair. We finally show the reorientation results for all the stations of the network, obtained using eight teleseismic events that occurred between January 2012 and May 2014.
... Seismic noise characterization is then a necessary step to assess detection and location performance of a seismic network that helps in its design and optimization (D'Alessandro et al., 2011;Vassallo et al., 2012;Stabile et al., 2013;De Landro et al., 2020). Among different applications requiring the need of optimally designed seismic networks, monitoring of induced seismicity associated with industrial activities is, by a societal point of view, the most sensitive one (Kraft and Deichmann, 2014;Priolo et al., 2015). In such applications, we generally deal with seismic sequences characterized by a large number of weak events (generally below magnitude 0); analyzing the spatiotemporal evolution of such sequences in real time is extremely important to manage the hazard posed by induced seismicity (Lee et al., 2019;Broccardo et al., 2020). ...
The background seismic noise can be generated by different sources such as, ocean waves (microseisms), atmospheric disturbances (strong wind and storms), and anthropogenic activities, temperature changes and magnetic field variations. Such disturbances are characterized by specific frequency bands, time occurrence (diurnal and seasonal variation), and site location (close to populated areas or to the coasts). Reducing the pernicious effect of these noise sources is one of the main challenges that seismologists and engineers need to face when designing seismic monitoring networks and, more specifically when selecting the hosting site of a seismic station. A solution to partially attenuate the seismic noise effect is achieved by deploying seismic stations in boreholes. A general law estimating the sufficient depth to gain to detect even low seismic events, highly masked by background noise, is fundamental for defining the capability of microseismic network. Here, we aim to characterize the seismic noise level at S. Potito-Cotignola in the Po Valley, Italy, from January 2019 to December 2021 recorded by a broadband seismic station at surface and a vertical array composed by six short-period three-component seismometers installed at depth ranging between 35 and 285 m in borehole. We compute the amplitude noise reduction as a function of depth for different frequencies and we evaluate the depth dependency of the signal to noise ratio for 18 seismic events, with different magnitude (from −0.1 to 2.9) and hypocentral distances (from 12.9 to 37.2 km). Results show that (1) the dependence of noise level with depth follows a logarithmic empirical trend and (2) most of the selected seismic events show that signal to noise ratio increases with depth. The empirical relationships we estimated can be used to help the design of microseismic monitoring networks in similar geological settings.
... The INGV has been charged with monitoring three areas of industrial activity (the Minerbio gas storage and the oil fields of Cavone and Val d'Agri: Braun et al., 2020;Carannante et al., 2020) during a 2-year experimental phase. Many other authors reported about the monitoring of industrial activity around the world (Mordret et al., 2014;Priolo et al., 2015, describe analysis of data from very dense ad-hoc networks), some of them reporting about clear episodes of induced seismicity (Maury et al., 1992;Keranen et al., 2013;van Thienen-Visser and Breunese, 2015, respectively for the Groningen gas field in the Nederlands, the Wilzetta oil field in Oklahoma, United States, and the Lacq gas field in France, among the others), some others developing models for computing stress changes due to well operations on the nearby faults (Zhao and Jha, 2019). This paper describes the work done in the first attempt of guidelines' application at the Cavone oil field during 2018 and 2019. ...
In this paper we describe the results of an experimental implementation of the recent guidelines issued by the Italian regulatory body for monitoring hydrocarbon production activities. In particular, we report about the pilot study on seismic, deformation, and pore pressure monitoring of the Mirandola hydrocarbon cultivation facility in Northern Italy. This site hosts the Cavone oil field that was speculated of possibly influencing the 2012 M L 5.8 Mirandola earthquake source. According to the guidelines, the monitoring center should analyse geophysical measurements related to seismicity, crustal deformation and pore pressure in quasi real-time (within 24–48 h). A traffic light system would then be used to regulate underground operations in case of detecting significant earthquakes (i.e., events with size and location included in critical ranges). For these 2-year period of guidelines experimentation, we analysed all different kinds of available data, and we tested the existence of possible relationship between their temporal trends. Despite the short time window and the scarce quantity of data collected, we performed the required analysis and extracted as much meaningful and statistically reliable information from the data. We discuss here the most important observations drawn from the monitoring results, and highlight the lessons learned by describing practical issues and limitations that we have encountered in carrying out the tasks as defined in the guidelines. Our main goal is to contribute to the discussion about how to better monitor the geophysical impact of this kind of anthropogenic activity. We point out the importance of a wider seismic network but, mostly, of borehole sensors to improve microseismic detection capabilities. Moreover, the lack of an assessment of background seismicity in an unperturbed situation -due to long life extraction activities- makes it difficult to get a proper picture of natural background seismic activity, which would be instead an essential reference information for a tectonically-active regions, such as Northern Italy.
... The deployment of high-density microseismic monitoring networks has been demonstrated to be a powerful approach to improve the detection performance of weak events [11][12][13][14][15][16][17][18] . In addition to the high density of stations, the main advantages of modern microseismic monitoring networks are: (1) the use of high quality sensors with a large dynamic range placed in shallow or deep boreholes which reduces the background noise level 18-20 ; (2) the availability of continuous data streams from each seismic station allowing for the real-time or off-line application of advanced detection 21-23 and location 24-30 techniques, which results in decreased magnitude of completeness and generation of massive microseismic catalogues of accurate located events. ...
Improving the capability of seismic network to detect weak seismic events is one of the timeless challenges in seismology: the greater is the number of detected and locatable seismic events, the greater insights on the mechanisms responsible for seismic activation may be gained. Here we implement and apply a single-station template matching algorithm to detect events belonging to the fluid-injection induced seismicity cluster located in the High Agri Valley, Southern Italy, using the continuous seismic data stream of the closest station of the INSIEME network. To take into account the diversity of waveforms, albeit belonging to the same seismic cluster, eight different master templates were adopted. Afterwards, using all the stations of the network, we provide a seismic catalogue consisting of 196 located earthquakes, in the magnitude range − 1.2 ≤ Ml ≤ 1.2, with a completeness magnitude Mc = − 0.5 ± 0.1. This rich seismic catalogue allows us to describe the damage zone of a SW dipping fault, characterized by a variety of fractures critically stressed in the dip range between ~ 45° and ~ 75°. The time-evolution of seismicity clearly shows seismic swarm distribution characteristics with many events of similar magnitude, and the seismicity well correlates with injection operational parameters (i.e. injected volumes and injection pressures).
... More recent cases of induced microseismicity in Europe, reported at different gas storage facilities 2,25 , did not exceed Mw 1.0. The general lack of induced seismicity observations at UGSs may be partially attributed to poor seismic monitoring 24 , but even well-monitored gas reservoirs, such as the Collalto reservoir, NE Italy, showed an almost complete absence of induced seismicity, with no microseismicity above M 0.0 within 3 km from the reservoir 26 . Another reason for the low seismogenic potential of gas storage operations could be that gas injection schedules are typically designed and engineered not to exceed the stress conditions existing prior to or during the original reservoir production. ...
The 2013 seismic sequence at the Castor injection platform offshore Spain, including three earthquakes of magnitude 4.1, occurred during the initial filling of a planned Underground Gas Storage facility. The Castor sequence is one of the most important cases of induced seis- micity in Europe and a rare example of seismicity induced by gas injection into a depleted oil field. Here we use advanced seismological techniques applied to an enhanced waveform dataset, to resolve the geometry of the faults, develop a greatly enlarged seismicity catalog and record details of the rupture kinematics. The sequence occurred by progressive fault failure and unlocking, with seismicity initially migrating away from the injection points, triggered by pore pressure diffusion, and then back again, breaking larger asperities loaded to higher stress and producing the largest earthquakes. Seismicity occurred almost exclusively on a secondary fault, located below the reservoir, dipping opposite from the reservoir bounding fault.
... In addition to NEI, OGS manages the Collalto Seismic Network, a local network with the aim of monitoring the seismicity in an area near the underground gas storage site of Montello-Collalto, located at the northern margin of the Venetian Plain. This network consists of 10 broadband seismological stations, all of which are equipped with borehole or posthole seismometers (Priolo et al., 2014). In total, almost 70 permanent stations in northeastern Italy provide seismic recordings in real time, as of 2021. ...
The application of earthquake recordings to the estimation of an event’s magnitude and the construction of rapid-response ground-motion maps requires an adequate classification of the recording stations in terms of their site response. For permanent stations, this information can be obtained from a sufficiently large database of past recordings.
In this work, we analyze more than 7300 three-component recordings collected between 1996 and 2017 by 67 permanent stations in northeastern Italy to assess their site amplification. The signals come from 368 earthquakes with a magnitude range of M 3.2–5.8 and a distance range of 10–300 km. We evaluate the frequency-dependent amplification function with respect to a reference station with a flat seismic noise horizontal-to-vertical spectral ratio. The evaluation relies on the decomposition of the S-wave amplitude spectra in terms of source, propagation, and site response. We solve the decomposition with a nonparametric, single-step generalized inversion in the frequency band 0.5–20 Hz. In addition, we compute the amplification factors for peak ground acceleration and velocity with respect to a well-established ground-motion prediction equation. The results highlight that only 11 stations show a relatively flat unitary response with respect to the reference site, whereas the frequency-averaged amplification function at 23 out of 67 stations exhibits a value larger than 2. We classified the sites according to their surface geology and geomorphological scenario and found that amplification affects not only stations installed on the alluvial soil but also several stations installed on what are assumed to be rock sites. Sites in caves and mines exhibit deamplification, whereas the stations with sensors in boreholes exhibit the typical interference pattern. A good correlation between the amplification factors and the frequency-averaged amplification functions suggests the possibility of predicting time-domain peak ground-motion values from amplification functions estimated by generalized inversion.
... We use the local earthquake catalog from Romano et al. (2019), which contains high-resolution relocations of 1,609 events with magnitudes ranging from −0.8 to 4.5, in the period January 2012 to October 2017. This catalog was produced using data from the Collalto Seismic Network (Priolo et al., 2015) and represents one of the most accurate, high quality, earthquake catalogs for this sector of the Southern Alps. ...
... In addition, there are many UGS facilities that are either under construction or planned across the world. This represents a potentially looming crisis since UGS operations can expose local communities to the potential risks of surface deformation and induced seismicity (Gaite et al., 2016;Priolo et al., 2015;Tang et al., 2018;Zhou et al., 2019;Jiang et al., 2020). Moreover, induced earthquakes in populated areas caused by other anthropogenic fluid injection and extraction activities appear to be growing in scale and frequency (e.g., Chen et al., 2017;Lee et al., 2019;Lei et al., 2019;McGarr et al., 2015;S. ...
The world's largest underground gas storage facility in Hutubi (HUGS), China, is a unique case where cyclic gas injection‐extraction induced both seismicity and ground deformation. To assess the potential for future induced seismicity, we develop a framework physically based on a well‐constrained hydro‐geomechanical model and on fully‐coupled poroelastic simulations. We first interpret the spatiotemporal distribution and focal mechanisms of induced earthquakes and take it as a key step and a premise to estimate the magnitude and location of the largest potential earthquake. The sharp increase in seismicity was controlled by poroelastic loading on secondary southwest‐dipping thrust faults with spatial scales too small to be resolved by 3D seismic surveys. Both operational and local geological factors affect the seismic productivity at the HUGS site, distinguishing it from most cases of seismicity induced by wastewater disposal and hydraulic fracturing. We then conduct slip tendency analyses for major faults imaged by the seismic data, including the largest reservoir‐bounding Hutubi fault hydraulically connected to injection wells. The reactivation potentials of these imaged faults are estimated to be extremely low. Accordingly, future seismicity would most likely occur on failure‐prone secondary faults in regions with positive stress perturbation due to poroelastic loading. The maximum magnitude likely depends on the spatial scales of the secondary faults. As the occurrence of detected earthquakes is spatially and temporally consistent with the simulated evolution of Coulomb stress perturbation, the location of the largest potential earthquake probably depends on the sizes of the poroelastic stressing regions.
... We use the local earthquake catalog from Romano et al. (2019), which contains high-resolution relocations of 1,609 events with magnitudes ranging from −0.8 to 4.5, in the period January 2012 to October 2017. This catalog was produced using data from the Collalto Seismic Network (Priolo et al., 2015) and represents one of the most accurate, high quality, earthquake catalogs for this sector of the Southern Alps. ...
Plain Language Summary
The natural water cycle, by changing how water is stored on the continents, can cause nonnegligible deformation at the Earth's surface. Redistribution of water masses has long been known to alter the state of stress in the crust and potentially modulate seismicity rates. However, the degree to which regional changes in groundwater storage influence crustal stresses and the occurrence of earthquakes at fault scales remains an open problem. We study a karst area located in a tectonically active region of Northern Italy, where plate convergence is accommodated across a complex system of faults and folds. We use GPS, hydrological, meteorological and seismological observations, integrated by hydrological and mechanical models, to show that there is a direct elastic connection between changes in groundwater storage, crustal deformation, and seismicity rates. We show that hydrologically active fractures and seismically active fractures might be disjoint, and that pore pressure propagation is not required to generate stress changes at seismogenic depths. Indeed, the convergence of water from upstream catchment toward permeable fractures connected to the surface can generate large pressure changes on the wall of these fractures, causing horizontal displacements and perturbations of the crustal stress that modulate background seismicity rates.
... Oltre a fornire un efficace servizio di allarme sismico per la Regione Veneto, dal 2012 OGS svolge anche un'attività di monitoraggio sismico locale in prossimità dello stoccaggio di gas metano di Collalto (TV), su commessa di Edison S.p.A. che gestisce l'impianto (Priolo et al., 2015). Le due attività sono ben distinte tra loro, per scopi e finanziamenti. ...
Seismic monitoring of the Veneto region recorded by the seismometric network of northeastern Italy managed by the National Institute of Oceanography and Applied Geophysics - OGS. Year 2016
... Oltre a fornire un efficace servizio di allarme sismico per la Regione Veneto, dal 2012 OGS svolge anche un'attività di monitoraggio sismico locale in prossimità dello stoccaggio di gas metano di Collalto (TV), su commessa di Edison Stoccaggio S.p.A. che gestisce l'impianto (Priolo et al., 2015). Le due attività sono ben distinte tra loro, per scopi e finanziamenti. ...
Seismic monitoring of the Veneto region recorded by the seismometric network of northeastern Italy managed by the National Institute of Oceanography and Applied Geophysics - OGS. Year 2018
... Dal 2012 OGSè impegnato nel monitoraggio e nello studio della microsismicità eventualmente indotta dalle attività di stoccaggio di gas metano nella concessione di Collalto (Treviso), oltre che della sismicità naturale presente nell'area circostante del Montello-Collalto, cheè densamente popolata e caratterizzata da un rilevante rischio sismico (Priolo et al. (2015); ). Infatti l'iniezione e l'estrazione di fluidi nel sottosuolo può farne variare la pressione in profondità rendendo instabili eventuali faglie e aumentando la possibilità di innescare terremoti. ...
Seismic monitoring of the Veneto region recorded by the seismometric network of northeastern Italy managed by the National Institute of Oceanography and Applied Geophysics - OGS. Year 2019
... larger seismic event here, the Mw 6.4, 1695 Asolo earthquake (see Fig. 1), is located at the foothills of the mountain range 340 delimited by the BVT front, but is in general associated with the westernmost portion of the Montello thrust, the Bassano-Corduna segment (Galadini et al., 2005;Burrato et al., 2008). Only recently local seismic networks (Priolo et al., 2015) and temporary seismic experiments (Anselmi et al., 2011;Danesi et al., 2015) have improved the imaging of faults at depth, indicating earthquakes with thrust focal mechanisms for both the Montello and Bassano-Valdobbiadene faults (Fig. 3). ...
Abstract. This study presents and discusses horizontal and vertical geodetic velocities for a low strain-rate region of the Southalpine thrust front in northeastern Italy obtained by integrating GPS, InSAR and leveling data. The area is characterized by the presence of sub-parallel, south verging thrusts, whose seismogenic potential is still poorly known. Horizontal GPS velocities show that this sector of the Eastern Southern Alps is undergoing ~ 1 mm/a of NW-SE shortening associated with the Adria-Eurasia plate convergence, but the horizontal GPS velocity gradient across the mountain front provide limited constraints on the geometry and slip-rate of the several sub-parallel thrusts. In terms of vertical velocities, the three geodetic methods provide consistent results showing a positive velocity gradient, of ~ 1.5 mm/a, across the mountain front, which can be hardly explained solely by isostatic processes. We developed a interseismic dislocation model, whose geometry is constrained by available subsurface geological reconstructions and instrumental seismicity. While a fraction of the measured uplift can be attributed to glacial and erosional isostatic processes, our results suggest that interseismic strain accumulation at the Montello and the Bassano-Valdobbiadene thrusts are significantly contributing to the measured uplift. The seismogenic potential of the Montello thrust turns out to be smaller than that of the Bassano-Valdobbiadene fault, whose estimated parameters (LD = 9.1 km and slip-rate = 2.1 mm/a) indicate a structure capable of potentially generating a Mw > 6.5 earthquake. These results demonstrate the importance of precise vertical ground velocity data for modeling interseismic strain accumulation in slowly deforming regions, where often seismological and geomorphological evidence of active tectonics is scarce or not conclusive.
... Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, 2012), which was the first Italian network providing data with open-access policy (http://oasis.crs.inogs.it, last access: January 2020; as reported in Priolo et al., 2015). ...
The High Agri Valley is a tectonically active area in southern Italy characterized by high seismic hazard related to fault systems capable of generating up to M=7 earthquakes (i.e. the 1857 Mw=7 Basilicata earthquake). In addition to the natural seismicity, two different clusters of induced microseismicity were recognized to be caused by industrial operations carried out in the area: (1) the water loading and unloading operations in the Pertusillo artificial reservoir and (2) the wastewater disposal at the Costa Molina 2 injection well. The twofold nature of the recorded seismicity in the High Agri Valley makes it an ideal study area to deepen the understanding of driving processes of both natural and anthropogenic earthquakes and to improve the current methodologies for the discrimination between natural and induced seismic events by collecting high-quality seismic data. Here we present the dataset gathered by the INSIEME seismic network that was installed in the High Agri Valley within the SIR-MIUR research project INSIEME (INduced Seismicity in Italy: Estimation, Monitoring, and sEismic risk mitigation). The seismic network was planned with the aim to study the two induced seismicity clusters and to collect a full range of open-access data to be shared with the whole scientific community. The seismic network is composed of eight stations deployed in an area of 17km×11km around the two clusters of induced microearthquakes, and it is equipped with triaxial weak-motion broadband sensors placed at different depths down to 50 m. It allows us to detect induced microearthquakes, local and regional earthquakes, and teleseismic events from continuous data streams transmitted in real time to the CNR-IMAA Data Centre. The network has been registered at the International Federation of Digital Seismograph Networks (FDSN) with code 3F. Data collected until the end of the INSIEME project (23 March 2019) are already released with open-access policy through the FDSN web services and are available from IRIS DMC (10.7914/SN/3F_2016; Stabile and INSIEME Team, 2016). Data collected after the project will be available with the permanent network code VD (10.7914/SN/VD, CNR IMAA Consiglio Nazionale delle Ricerche, 2019) as part of the High Agri Valley geophysical Observatory (HAVO), a multi-parametric network managed by the CNR-IMAA research institute.
... First experiences made during the recently concluded test-phase of the Minerbio concession are described by Carannante et al. (2019, this volume), who emphasize the improvement in earthquake detection capability due to the upgrade of the seismographic network of the plant operator linked to the requirements posed by ILG, and to the integration of available stations of the INGV national network. Other relevant cases in Italy, where geophysical monitoring has been extensively running for several years under systematic protocols, include the gas storage at Collalto (Priolo et al. 2015;Moratto et al. 2019;Romano et al. 2019) and the planned geothermal site of Torre Alfina (Braun et al. 2018a). ...
Public concern about anthropogenic seismicity 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 regulations regarding hydrocarbon extraction, waste-water injection and gas storage that could also be adapted to other technologies, such as dams, geothermal systems, CO2 storage, and mining. The ILG describe the framework for the different actors involved in monitoring activities, their relationship and responsibilities, the procedure to be followed in case of variations of monitored parameters, the need for in-depth scientific analyses, the definition of different alert levels, their meaning 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 authorities and industrial operator on the basis of evaluation 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 implementation. Attention areas of adjacent reservoirs, possibly licenced to different operators, may overlap, hence making 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 active production. Magnitude – a critical parameter used to define a possible step-up in activation levels – has inherent uncertainty and can be evaluated using different 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 triggered tectonic events.
... Qui descriveremo brevemente come si svolge l'analisi dei dati. Il dettaglio completo delle procedure e operazioni è descritto in Garbin e Priolo (2013) e Priolo et al. (2015b). ...
... Qui descriveremo brevemente come si svolge l'analisi dei dati. Il dettaglio completo delle procedure e operazioni è descritto in Garbin e Priolo (2013) e Priolo et al. (2015b). ...
... The spatio-temporal correlation between the seismicity and a cushion gas injection test on the Castor UGS site suggested seismicity to be triggered by the injection (Cesca et al., 2014). The ongoing monitoring of the Collalto UGS field, Italy, where the gas is stored in a depleted reservoir, has not detected any relevant microseismicity so far (Priolo et al., 2015). Decadal UGS activities in several northern Adriatic reservoirs (Italy) with a pressure p > p initial (up to ~ 110% p initial ) have never ARMA 19-1991 Gas storage in compartmentalized reservoirs: a numerical investigation on possible "unexpected" fault activation been associated to seismicity, with a maximum pressure that could safely overcome the p initial bound (Castelletto et al., 2013). ...
Underground gas storage (UGS) is a practice that is becoming widely implemented to cope with seasonal peaks of gas consumption. When the target reservoir is located in a faulted basin, a major safety issue concerns the reactivation of pre-existing faults, possibly inducing (micro-) seismicity. Faults are reactivated when the shear stress exceeds the limiting acceptable strength. It has been observed in The Netherlands that this occurrence can happen “unexpectedly” during the life of a UGS reservoir, i.e. when the actual stress regime is not expected to reach the failure condition. A numerical analysis by a 3D FE-IE elasto-plastic geomechanical simulator has been carried out to cast light in this respect, by investigating the mechanisms and the critical factors that can be responsible for a fault reactivation during the various UGS stages. Generally, the settings (in terms of reservoir and fault geometry, geomechanical parameters, and pressure change distribution) more prone to fault activation during primary production are also the most critical ones during cushion gas injection and UGS cycles.
... Associated seismicity induced at different scales has been documented in geologic storage of carbon dioxide [36,38,48,49,58], geothermal production fields [20,23,41,57], conventional and unconventional hydrocarbon reservoirs [21,25,31], and UGS plants [8,29,40]. A growing interest on the relation between such operations and fault activation has led to the establishment of specific monitoring networks to collect data of micro-seismic activity, e.g., [42]. On the other hand, modeling tools have been recently developed to simulate the possible inception of fault motion [2,5,14,26]. ...
The reactivation of faults and the generation of fractures can be caused by stress changes due to injection and/or production of fluids into and/or from the subsurface. The simulation of these processes, which could be associated with (micro-)seismicity, is affected by a high uncertainty. The aim of this work is at developing a mathematical framework to quantify and possibly reduce the prior modeling uncertainties by assimilation of seismic data. The mechanics of fault (re-)activation is simulated by a Finite Element (FE) numerical model where the discontinuous displacements between the fault surfaces are suitably considered using appropriate Interface Elements (IEs). The study is carried out by using a stochastic approach, with a global sensitivity analysis (gSA) based on Sobol’ indices initially performed to estimate the influence of the input parameters on the model solution. Then, a Markov Chain Monte Carlo (MCMC) sampling technique based on the generalized Polynomial Chaos expansion (gPC) surrogate solution is used to update the prior information conditioned on seismic observations. The methodology is tested on a 3D synthetic test case. The uncertain input is the natural stress regime and the Mohr-Coulomb parameters characterizing the fault activation criterion. A good reduction of the prior uncertainty is obtained, showing that the assimilation of seismic data can have a promising potential for improving the subsurface characterization.
... Inoltre, sempre per quanto riguarda l'aspetto scientifico-divulgativo, si segnala che i primi risultati ottenuti dall'analisi dei dati della RSC sono stati pubblicati su riviste nazionali e internazionali (Priolo et al., 2015a;Romano et al., 2015), oltre che presentati alla comunità scientifica in numerosi convegni, in Italia e all'estero (Appendice H). I file in formato pdf delle pubblicazioni sono scaricabili dal sito della RSC nella sezione Materiale Scientifico e Documentazione. ...
Edison Stoccaggio S.p.A. Rete di rilevamento sismico finalizzata al monitoraggio della sismicità naturale e microsismicità indotta presso la concessione di stoccaggio gas metano denominata "Collalto Stoccaggio" (TV) Anno di esercizio 2015-Seconda relazione annuale Prescr. min. di cui alla nota DVA-2013-0005150 dd. 27/03/2013 Responsabile scientifico del progetto: Enrico Priolo Documento redatto con il contributo di:
... Modeling the geomechanical effects of the cyclic loading due to summer injection and winter withdrawal is the object of several recent works, e.g., [56][57][58][59], and is of paramount importance for an optimal management and schedule of the storage activities. One of the main issues is the seismicity that has been recognized to be possibly induced or triggered by fault activation during the UGS operations [60][61][62][63]. Fig. 10 shows the geomechanical model of a faulted UGS site in Italy. ...
The efficient simulation of fault and fracture mechanics is a key issue in several applications and is attracting a growing interest by the scientific community. Using a formulation based on Lagrange multipliers, the Jacobian matrix resulting from the Finite Element discretization of the governing equations has a non-symmetric generalized saddle-point structure. In this work, we propose a family of block preconditioners to accelerate the convergence of Krylov methods for such problems. We critically review possible advantages and difficulties of using various Schur complement approximations, based on both physical and algebraic considerations. The proposed approaches are tested in a number of real-world applications, showing their robustness and efficiency also in large-size and ill-conditioned problems.
... Ø Since 2012, OGS has been involved in monitoring and studying the microseismicity possibly induced by the gas storage activities located at Collalto, nearby the town of Treviso in Northeastern Italy (Priolo et al., 2015). For detailed info about the network visit the website http://rete-collalto.crs.inogs.it ...
... The present local seismicity (OGS-RSC Working Group 2012) is shown in Fig. 2. The seismicity is monitored with a local network due to the presence of a natural gas storage concession. Details on the relation between gas pumping and seismicity can be found in Priolo et al. (2015). The magnitudes range from -1.8 to 4.5, with average magnitude of 0.6 in the period 2012-2017. ...
Ten years’ geodetic observations (2006–2016) in a natural cave of the Cansiglio Plateau (Bus de la Genziana), a limestone karstic area in northeastern Italy, are discussed. The area is of medium–high seismic risk: a strong earthquake in 1936 below the plateau (Mm = 6.2) and the 1976 disastrous Friuli earthquake (Mm = 6.5) are recent events. At the foothills of the karstic massif, three springs emerge, with average flow from 5 to 10 m³/s, and which are the sources of a river. The tiltmeter station is set in a natural cavity that is part of a karstic system. From March 2013, a multiparametric logger (temperature, stage, electrical conductivity) was installed in the siphon at the bottom of the cave to discover the underground hydrodynamics. The tilt records include signals induced by hydrologic and tectonic effects. The tiltmeter signals have a clear correlation to the rainfall, the discharge series of the river and the data recorded by multiparametric loggers. Additionally, the data of a permanent GPS station located on the southern slopes of the Cansiglio Massif (CANV) show also a clear correspondence with the river level. The fast water infiltration into the epikarst, closely related to daily rainfall, is distinguished in the tilt records from the characteristic time evolution of the karstic springs, which have an impulsive level increase with successive exponential decay. It demonstrates the usefulness of geodetic measurements to reveal the hydrological response of the karst. One outcome of the work is that the tiltmeters can be used as proxies for the presence of flow channels and the pressure that builds up due to the water flow. With 10 years of data, a new multidisciplinary frontier was opened between the geodetic studies and the karstic hydrogeology to obtain a more complete geologic description of the karst plateau.
... In recent years, seismicity induced by human activities has become an important topic of interest to the general public, including the controlled explosions related to mining or construction (Fletcher & McGarr, 2005;Latorre et al., 2014;Li et al., 2007;Shen et al., 2008), induced earthquakes by the impoundment of large water reservoirs (Do Nascimento et al., 2005;Ge et al., 2009;Gough & Gough, 1970;Guha, 2013), and activities related to the energy field production ( Bardainne et al., 2008;Brodsky & Lajoie, 2013;Clarke et al., 2014;Deichmann & Giardini, 2009;Ellsworth, 2013;Gan & Frohlich, 2013;Healy et al., 1968;Kim, 2013;Priolo et al., 2015;Shirzaei et al., 2016;Tadokoro et al., 2000;Walsh & Zoback, 2015). At the same time, those induced seismic activities have also offered great opportunities to explore earthquake physics. ...
Hutubi gas field, the largest gas storage field in China, has been operated on annual injection/extraction cycles since 9 June 2013. We study the seismicity near the gas field from 9 June 2013 to 22 October 2015, a time span that the gas field has experienced three injection periods and two extraction periods, and explore its physical mechanism based on the relationship between seismicity and field operation. We identify 273 events (ML > 1) in the region within 10 km of the gas field, with 97% of those occurring in the first two injection periods, 0.4% in the third injection period, and 1% in the two extraction periods. Seismicity in the first two injection periods occurs mostly as shallow clusters (focal depth < 2 km) at two locations: with one along the fault that marks the southern boundary of the gas field and the other about 2 km south to the southeastern tip of the gas field with the seismicity distributed along north-south direction. The seismicity does not correlate with total gas injection volume, injection rate, or well pressure. It instead occurs 11-17 hr after simultaneous abrupt increases/decreases of gas injection rate and well pressure in the field operation in the first two injection periods when some accumulative injection has reached. Such relationship is consistent with a physical mechanism that the seismicity near Hutubi gas field is induced on pore-pressured faults with a rate- and state-dependent friction law through an abrupt change of stress in elastic and undrained poroelastic responses to simultaneous abrupt changes of injection rate and well pressure. Our study also points to the possibility that induced seismicity may be controllable in some practical field operations.
... The present local seismicity (OGS-RSC Working Group 2012) is shown in Fig. 2. The seismicity is monitored with a local network due to the presence of a natural gas storage concession. Details on the relation between gas pumping and seismicity can be found in Priolo et al. (2015). The magnitudes range from -1.8 to 4.5, with average magnitude of 0.6 in the period 2012-2017. ...
Ten years’ geodetic observations (2006–2016) in a natural cave of the Cansiglio Plateau (Bus de la Genziana), a limestone karstic area in northeastern Italy, are discussed. The area is of medium–high seismic risk: a strong earthquake in 1936 below the plateau (Mm = 6.2) and the 1976 disastrous Friuli earthquake (Mm = 6.5) are recent events. At the foothills of the karstic massif, three springs emerge, with average flow from 5 to 10 m3/s, and which are the sources of a river. The tiltmeter station is set in a natural cavity that is part of a karstic system. From March 2013, a multiparametric logger (temperature, stage, electrical conductivity) was installed in the siphon at the bottom of the cave to discover the underground hydrodynamics. The tilt records include signals induced by hydrologic and tectonic effects. The tiltmeter signals have a clear correlation to the rainfall, the discharge series of the river and the data recorded by multiparametric loggers. Additionally, the data of a permanent GPS station located on the southern slopes of the Cansiglio Massif (CANV) show also a clear correspondence with the river level. The fast water infiltration into the epikarst, closely related to daily rainfall, is distinguished in the tilt records from the characteristic time evolution of the karstic springs, which have an impulsive level increase with successive exponential decay. It demonstrates the usefulness of geodetic measurements to reveal the hydrological response of the karst. One outcome of the work is that the tiltmeters can be used as proxies for the presence of flow channels and the pressure that builds up due to the water flow. With 10 years of data, a new multidisciplinary frontier was opened between the geodetic studies and the karstic hydrogeology to obtain a more complete geologic description of the karst plateau.
SharedIt link to article: https://rdcu.be/bbZvk
... The fourth scenario is in connection with underground storage of natural gas, adopted worldwide to meet seasonal variations in demand, which requires cyclic injection and extraction of natural gas underground (e.g. Priolo et al., 2015). For instance, near the Hutubi gas reservoir in Xinjiang, the largest underground repository for natural gas in China, a sequence of earthquakes occurred soon after the injection was initiated in 2013, with the largest magnitude of ML3.5 (Figure 3). ...
It has long been known that human activities such as waste fluid disposal and reservoir impoundment may cause earthquakes. Recently, anthropogenic activities to tackle the increasing energy demand and to address climate change issues are also reported to induce earthquakes. These activities have a common attribute in that fluids are injected and extracted underground and induce spatiotemporal changes of pore pressure and stress, which may cause slip on faults. Induced earthquakes not only pose significant impacts on seismic hazard assessment and preparation, but also raise the question to the society as how to balance the economic needs of resources development and the public’s concerns about potential environmental impacts. Here we review the observations of fluid-injection/extraction induced earthquakes, ground deformation associated with these activities, and their physical mechanisms. Furthermore, we discuss the influences of induced earthquakes on seismic hazard models, regulatory policies on these anthropogenic activities, and current development of academic, industrial and government initiatives and collaborations in order to understand this intriguing phenomenon and address associated challenges.
... Three institutions (the National Institute of Oceanography and Experimental Geophysics -OGS, the Geological Seismic Soil Survey of Emilia-Romagna Region RER, and the Institute of Methodologies for Environmental Research (IMAA) of the National Council of Research (CNR) CNR-IMAA) cooperated in the installation and maintenance of the NISBAS stations. The stations included within NISBAS (and listed in Tab. 1) belong to three different networks: the North-East Italy Regional Broad Band Seismic Network NI (Priolo et al., 2005;Bragato et al., 2011), the University of Basilicata (UNIBAS) network BA (Attolico et al., 2010), and the Collalto permanent network EV (Priolo et al., 2015b). The stations are the following: ...
... More information, including the examples of communication to population are available at the site http://rete-collalto.crs.inogs.it/en, while the scientific outcomes of the network are described in Priolo et al. (2015) ...
We introduce a Bayesian algorithm designed to integrate earthquake magnitudes of the same type reported by various seismic networks, aiming to create unified and standardized catalogs suitable for widespread use. The fundamental concept underpinning this algorithm is the utilization of the inherent consistency within each individual network’s magnitude determination process. Assuming that the magnitudes for an earthquake measured by all networks conform to a Gaussian distribution, with a linear function of the unknown true magnitude serving as its mean, we derive the posterior probability distribution of the true magnitude under four different assumptions for the prior distribution: the uninformative uniform distribution, the unbounded Gutenberg–Richter (GR) magnitude–frequency law, the GR magnitude–frequency relationship restricted by the detection rate, and the truncated GR law as priors. We assess the robustness of the method by a test on several synthetic catalogs and then use it to merge the catalogs compiled by five seismic networks in Italy. The results demonstrate that our proposed magnitude-merging algorithm effectively combines the catalogs, resulting in robust and unified data sets that are suitable for seismic hazard assessment and seismicity analysis.
The 1695 Mw 6.4 Asolano earthquake is the southernmost of the six largest earthquakes to have occurred in northeast Italy or nearby (the others being 1348 Mw 6.6 Eastern Alps; 1511 Mw 6.3 Friuli-Slovenia; 1873 Mw 6.2 Alpago-Cansiglio; 1936 Mw 6.1 Alpago-Cansiglio; 1976 Mw 6.4 Friuli). The 1695 earthquake is generally associated with the Montello thrust, with most recent studies locating it on the eastern slope of Montello Hill. A full-scale reappraisal of all available historical data leads this study to a more robust macroseismic localization of the 1695 earthquake and to open toward other possible locations of the seismic source that produced it. In particular, it becomes feasible to place its epicenter at the foothills of the Monte Grappa massif, the major morphological expression of the Bassano–Valdobbiadene thrust fault. Here, we describe the reasons that make this fault a possible alternative to previous hypotheses.
In a comment on our manuscript published three years ago (Moulin & Benedetti [2018] https://doi.org/10.1029/2018TC004958), the authors raise concern about so‐called “mis‐interpreted alluvial and tectonic structures,” and conclude that these issues “invalidate all the consequent interpretations on the deformation rates.” Two points raised by the comment are acknowledged, and affect our results only by slightly reducing (by at most 15%) the Late Pleistocene shortening‐rate across the Eastern Southern Alps. The others issues raised by the comment are mainly dealing with the literature review, and alternative interpretations. Herein, we provide additional information to support our interpretations, and to relate our observations to existing data. Most importantly, our results do not call into question the existing consensus on both the crustal architecture of the Eastern Southern Alps, and the rate of recent shortening.
Determining saturation and pore pressure is relevant for hydrocarbon production as well as natural gas and CO2 storage. In this context seismic methods provide spatially distributed data used to determine gas and fluid migration. A method is developed that allows to determine saturation and reservoir pressure from seismic data, more precisely from rock physical attributes that are velocity, attenuation and density. Two rock physical models based on Hertz-Mindlin-Gassmann and Biot-Gassmann are developed. Both generate poroelastic attributes from pore pressure, gas saturation and other rock-physical parameters. The rock physical models are inverted with deep neural networks to derive e.g. saturation, pore pressure and porosity from rock physical attributes. The method is demonstrated with a 65 m deep unconsolidated high porosity reservoir at the Svelvik ridge, Norway. Tests for the most suitable structure of the neural network are carried out. Saturation and pressure can be meaningfully determined under condition of a gas-free baseline with known pressure and data from an accurate seismic campaign, preferably cross-well seismic. Including seismic attenuation increases the accuracy. The training requires hours, predictions just a few seconds, allowing for rapid interpretation of seismic results.
This study presents and discusses horizontal and vertical geodetic velocities for a low strain rate region of the south Alpine thrust front in northeastern Italy obtained by integrating GPS, interferometric synthetic aperture radar (InSAR) and leveling data. The area is characterized by the presence of subparallel, south-verging thrusts whose seismogenic potential is still poorly known. Horizontal GPS velocities show that this sector of the eastern Southern Alps is undergoing ∼1 mm a-1 of NW–SE shortening associated with the Adria–Eurasia plate convergence, but the horizontal GPS velocity gradient across the mountain front provides limited constraints on the geometry and slip rate of the several subparallel thrusts. In terms of vertical velocities, the three geodetic methods provide consistent results showing a positive velocity gradient, of ∼ 1.5 mm a-1, across the mountain front, which can hardly be explained solely by isostatic processes. We developed an interseismic dislocation model whose geometry is constrained by available subsurface geological reconstructions and instrumental seismicity. While a fraction of the measured uplift can be attributed to glacial and erosional isostatic processes, our results suggest that interseismic strain accumulation at the Montello and the Bassano–Valdobbiadene thrusts it significantly contributing to the measured uplift. The seismogenic potential of the Montello thrust turns out to be smaller than that of the Bassano–Valdobbiadene fault, whose estimated parameters (locking depth equals 9.1 km and slip rate equals 2.1 mm a-1) indicate a structure capable of potentially generating a Mw>6.5 earthquake. These results demonstrate the importance of precise vertical ground velocity data for modeling interseismic strain accumulation in slowly deforming regions where seismological and geomorphological evidence of active tectonics is often scarce or not conclusive.
The High Agri Valley is a tectonically active area in southern Italy characterized by high seismic hazard related to fault systems capable of generating up to M=7 earthquakes (i.e., the 1857 Mw 7 Basilicata earthquake). In addition to the natural seismicity, two different clusters of induced microseismicity were recognized to be caused by industrial operations carried out in the area: (1) the water loading and unloading operations in the Pertusillo artificial reservoir; (2) the wastewater disposal at the Costa Molina 2 injection well. The twofold nature of the recorded seismicity in the High Agri Valley makes it an ideal study area to deepen the understanding of nucleation processes of both natural and anthropogenic earthquakes and to improve the current methodologies for the discrimination between natural and induced seismic events by collecting high quality seismic data. Here we present the dataset gathered by the INSIEME seismic network that was installed in the High Agri Valley within the SIR-MIUR research project INSIEME (INduced Seismicity in Italy: Estimation, Monitoring, and sEismic risk mitigation). The seismic network was planned with the aim to study the two induced seismicity clusters and to collect a full-range of open-access data to be shared with the whole scientific community. The seismic network is composed by 8 stations deployed in an area of 17 km x 11 km around the two clusters of induced microearthquakes and it is equipped with triaxial weak-motion broadband sensors placed at different depths down to 50 m. It allows to detect induced microearthquakes, local/regional earthquakes, and teleseisms from continuous data streams transmitted in real-time to the CNR-IMAA Data Centre. The network has been registered at the International Federation of Digital Seismograph Networks (FDSN) with code 3F. Data collected until the end of the INSIEME project (2019-03-23) are already released with open-access policy through the FDSN webservices and are available from http://www.fdsn.org/networks/detail/3F_2016 (https://doi.org/10.7914/SN/3F_2016; Stabile et al., 2016).
This paper explores (full-) waveform inversion in passive seismics to simultaneously optimize the source parameters of seismic events together with the properties of the medium of wave propagation. A heuristic optimization algorithm inspired in iterative design is proposed, which incorporates ideas from particle swarm optimization and variable projection. The algorithm is designed to accelerate convergence, improve stability and robustness, and minimize the number of user-defined parameters. The performance of the algorithm is illustrated with a real data example of hydraulic stimulation monitoring using a surface array of seismic receivers. In this example, only the locations of the receivers are known. The inversion is targeted to jointly optimize the parameters of a viscoelastic velocity model, associated models of receiver residual statics, wavelet signatures for direct compressional and shear arrivals, spatiotemporal locations of the input seismic events, and their corresponding moment tensors. Velocity model and locations are compared to estimations of the same parameters previously obtained through a well-established workflow using decoupled inversions. Results from both approaches show consistency. The main advantage of the joint approach is, therefore, the possibility of incorporating additional unknowns into the optimization to obtain self-consistent solutions using a single inversion process.
The eastern Southern Alps are located at the northern tip of the Adria microplate, which imposes 2.0–2.5 mm/year of N-S-convergence relative to stable Eurasia. We map surface evidence of recent folding/faulting in this area from a 5-m Digital Elevation Model (DEM). In the eastern part of the belt, observations reveal a 30-km-wide zone of active folding composed of at least five growing anticlines. The most recent ones warped the postglacial alluvial surface by <10 m. Combining these findings with published geological and geophysical data allows us to infer that active thrusting occurs along a single deeply rooted thrust, which accommodates the indentation of the Adriatic crust. Resolving the observed pattern of uplift on the inferred fault geometry indicates that NNE-SSW shortening across the eastern Southern Alps has occurred at a rate of about 1.5 mm/year over the postglacial period. On the other hand, a balanced cross section for the eastern Southern Alps at the scale of the upper crust constrains a minimum of 43 km of finite shortening over the last 14 Ma, yielding a shortening rate of about 3 mm/year, which is 2 times higher than the postglacial shortening rate. This decrease in the shortening rate is associated to the Pleistocene activation of new thrusts that is compatible with a change in the direction of compression. The inferred local change in the kinematics of thrusting during the Pleistocene is consistent with a change from Nubia-imposed to Adria-imposed convergence indicating that the fragmentation of the Adriatic promontory could have occurred 1–2 Ma ago.
We provide a present-day surface-kinematics model for the Alpine region and surroundings based on a high-level data analysis of about 300 geodetic stations continuously operating over more than 12 years. This model includes a deformation model, a continuous surface-kinematic (velocity) field, and a strain field consistently assessed for the entire Alpine mountain belt. Special care is given to the use of the newest Global Navigation Satellite Systems (GNSS) processing standards to determine high-precision 3-D station coordinates. The coordinate solution refers to the reference frame IGb08, epoch 2010.0. The mean precision of the station positions at the reference epoch is ±1.1 mm in N and E and ±2.3 mm in height. The mean precision of the station velocities is ±0.2 mm a-1 in N and E and ±0.4 mm a-1 in height. The deformation model is derived from the point-wise station velocities using a geodetic least-squares collocation (LSC) approach with empirically determined covariance functions. According to our results, no significant horizontal deformation is detected in the Western Alps, while across the Southern and Eastern Alps the deformation vectors describe a progressive eastward rotation towards Pannonia. This kinematic pattern also makes evident an increasing magnitude of the deformation from 0.1 mm a-1 in the western part of Switzerland up to about 1.3 mm a-1 in the Austrian Alps. The largest shortening is observed along the southern front of the Eastern Alps (in the northern area of the Venetian-Friuli Basin) and in the northern part of the Apennine Peninsula, where rates reach 2 and 3 mm a-1, respectively. The average accuracy of the horizontal deformation model is ±0.2 mm a-1. Regarding the vertical kinematics, our results clearly show an ongoing average uplift rate of 1.8 mm a-1 of the entire mountain chain, with the exception of the southern part of the Western Alps, where no significant uplift (less than 0.5 mm a-1) is detected. The fastest uplift rates (more than 2 mm a-1) occur in the central area of the Western Alps, in the Swiss Alps, and in the Southern Alps in the boundary region between Switzerland, Austria, and Italy. The general uplift observed across the Alpine mountain chain decreases towards the outer regions to stable values between 0.0 and 0.5 mm a-1 and, in some cases, to subsidence like in the Liguro-Provençal and Vienna basins, where vertical rates of -0.8 and -0.3 mm a-1 are observed, respectively. In the surrounding region, three regional subsidence regimes are identified: the Rhône-Bresse Graben with -0.8 mm a-1, the Rhine Graben with -1.3 mm a-1, and the Venetian-Friuli Basin with -1.5 mm a-1. The estimated uncertainty of our vertical motion model across the Alpine mountain belt is about ±0.3 mm a-1. The strain field inferred from the deformation model shows two main contrasting strain regimes: (i) shortening across the south-eastern front of the Alps and the northern part of the Dinarides and (ii) extension in the Apennines. The pattern of the principal strain axes indicates that the compression directions are more or less perpendicular to the thrust belt fronts, reaching maximum values of 20×10-9 a-1 in the Venetian-Friuli and Po basins. Across the Alpine mountain belt, we observe a slight dilatation regime in the Western Alps, which smoothly changes to a contraction regime in western Austria and southern Germany, reaching maximum shortening values of 6×10-9 a-1 in north-eastern Austria. The numerical results of this study are available at https://doi.pangaea.de/10.1594/PANGAEA.886889.
Foreword
Thirty years ago, in 1985, the compilation of the "Catalogo dei Terremoti Italiani dall’anno 1000 al 1980" (Catalogue of Italian Earthquakes from the year 1000 to 1980) in the framework of the “Progetto Finalizzato Geodinamica” was completed and published by Daniele Postpischl (Postpischl, 1985a). The Working Group that authored the catalogue had the goal of verifying the information on Italian earthquakes listed in different available catalogues, in particular the ENEL (1977) one, and compile a new, state-of-the-art catalogue. At the conclusion of that work, which had appeared as preliminary with respect to the initial goal, the entire, almost forgotten subject area of historical seismology had emerged and “the first concrete advancements in the still long course of the research, towards the development of final products” were represented by the catalogue and the monographs on large earthquakes collected in the “Atlas of isoseismal maps of Italian earthquakes” (Postpischl, 1985b).
The possibility of having final products was rapidly abandoned, as testified by the long process that has led to the current version of the Italian Parametric Earthquake Catalogue, which inherited that epoch. Through years the possibilities of improving the knowledge on earthquakes already known to the seismological tradition have been - and still are - manifold, and new research strategies have developed.
The new version of the Catalogue, after thirty years, is a further important contribution to the advancements of the understanding of the seismicity of the Italian territory, the definition of seismogenic processes, the identification and characterization of active structures and the improvements of seismic hazard assessment.
The first version of the Parametric Catalogue of Italian Earthquakes (Catalogo Parametrico dei Terremoti Italiani, CPTI99; CPTI Working Group, 1999) was published in July 1999. It aimed at unifying and homogenizing, by using the same parameterization procedures for all the events, the information on Italian earthquakes since then produced by different investigators or reported by different catalogues (NT4.1, Camassi and Stucchi, 1997; CFTI 1 and 2, Boschi et al., 1995; 1997).
In 2004, the second version CPTI04 (CPTI Working Group, 2004) was published as the catalogue to be used in the framework of the Italian seismic hazard assessment MPS04 (MPS Working Group, 2004; Stucchi et al., 2011). CPTI04 was indeed new only as concerns the 1981-2002 portion, the remaining portion being the same as CPTI99 with the exception of the conversion of Ms to Mw with empirical relationships. Some experimental and/or partial version were then released within INGV or to specific research projects.
The third published version, named CPTI11 (Rovida et al., 2011), was released in December 2011. Together with a remarkable update of the input data, both macroseismic (collected in the 2011 release of Italian Macroseismic Database DBMI11; Locati et la, 2011) and instrumental, the most important innovations with respect to previous versions regarded the catalogue structure, consisting of three sets of earthquake parameters, i.e. macroseismic, instrumental, and preferred ones, and the inclusion of records related to many fore- and after-shocks. Nonetheless, for time constraints only studies contributing macroseismic data published before 2007 were taken into account and neither the empirical conversion relations for homogenizing instrumental magnitudes to Mw nor the calibration used to assess parameters from macroseismic data - except the experimental application of the method by di Bakun e Wentworth (1997) to a few offshore earthquakes - were updated.
Thanks to the improved methodologies developed in the framework of some European projects and, mostly, to the wealth of new macroseismic data published in the last five years, together with revised calibrations of instrumental magnitudes, a new important update of the catalogue, as well as a new release of the companion macroseismic database DBMI, has been released as CPTI15.
The paper discusses the seismogenic characteristics of NE Italy related to earthquakes
with Mw≥5.5, and the geometry of the related sources re-drawn by following the DISS
standard procedure. Therefore, this paper represents an update of a previous work
which investigated the Prealpine area between the Lessini Mountains and the Italian-
Slovenian border, and defined the seismogenic sources potentially responsible for
earthquakes with Mw≥6 within the GNDT-2000 project. For inclusion in the DISS, the
sources of that previous work have been processed following a 3-step process, which
is a routine procedure used each time the parameters of a seismogenic source are taken
from published works. The first step was a consistency check of the source dimensions
(aspect ratio, from length/width relationships and according to the fault type), of their
position and geometry (minimum and maximum depth and dip), and of some
seismological parameters of the expected/associated earthquakes (slip, Mw from both
Wells and Coppersmith’s and Hanks and Kanamori’s relationships, and seismic
moment). All these parameters were verified by using the Fault Studio software. The
second step involved the inclusion of seismological information, such as the measured
stress drop, to infer slip on the fault plane and rupture area and to compare these
parameters with the rupture area hypothesised on the basis of the geological
information. The third step of the data processing deals with the analysis of the
intermediate size historical seismicity (5.5≤Mw≤6.0) and the possible association with
faults belonging to the identified active thrust systems of the eastern Southalpine
Chain front or to more internal faults (both thrust and strike-slip faults) not included
in the data set of the previous work.
Unconventional oil and gas production provides a rapidly growing energy source; however, high-production states in the United
States, such as Oklahoma, face sharply rising numbers of earthquakes. Subsurface pressure data required to unequivocally link
earthquakes to wastewater injection are rarely accessible. Here we use seismicity and hydrogeological models to show that
fluid migration from high-rate disposal wells in Oklahoma is potentially responsible for the largest swarm. Earthquake hypocenters
occur within disposal formations and upper basement, between 2- and 5-kilometer depth. The modeled fluid pressure perturbation
propagates throughout the same depth range and tracks earthquakes to distances of 35 kilometers, with a triggering threshold
of ~0.07 megapascals. Although thousands of disposal wells operate aseismically, four of the highest-rate wells are capable
of inducing 20% of 2008 to 2013 central U.S. seismicity.
The most common observations of reservoir‐induced seismicity (RIS) by filling artificial lakes are generally associated with the initial impoundment of the lake or the lake level increase above a previous maximum. Rarely, RIS persists for many years without a decrease in frequency or magnitude; if this occurs, it is called “protracted” or “continued” seismicity. Pertusillo artificial lake in high Agri Valley (southern Italy) is a small reservoir with a water column that fluctuates yearly by about 10–15 m (on average), corresponding to a pressure perturbation at the bottom of the lake of 0.10–0.15 MPa. Although the reservoir was filled in 1963, the microearthquake activity still occurring around the lake allows the categorization of such RIS as continued seismicity. We collected all microearthquakes (ML≤2.7) recorded near the reservoir by two different seismic networks from January 2005 to June 2012 and analyzed their frequency–magnitude distribution, which showed a b value (b=1.40) much higher than that expected for the investigated area. Even though the spatial seismicity pattern shows two distinct clusters to the northeast and southwest of the lake, we found that only the southwest seismicity is significantly correlated with the water level. The findings suggest that the physical driving mechanism is the 1D pore fluid pressure diffusion along the northeast–southwest fault zones, connecting the reservoir to the southern termination of the Monti della Maddalena fault system, with an average hydraulic diffusivity of ∼7.8 m2/s.
The Venetian part of the Southern Alps (N Italy) is a Neogene south-vergent thrust belt. The minimum shortening of the chain is 30 km. The thrusts trend N60°-80°E and show an inherited N10°W-N10°E normal fault pattern of the Mesozoic continental margin. These earlier features strongly controlled the evolution of the following oblique thrust belt. Structural undulations along strike of folds and thrusts occur in correspondence to Mesozoic faults, thickness and facies variations. The thrusts are arranged in an imbricate fan geometry. A frontal triangle zone laterally ends at transfer faults. Earlier stages of the thrust belt were characterized by frontal triangle zones which have later been involved and cut by the progression of the internal thrusts.
New geomorphological and structural data permitted to define the active
faulting framework of the eastern Southern Alps (NE Italy). All the
active faults detected in the investigated area are thrust segments of
the complex thrust system, which has been responsible for the latest
building of the Eastern Southalpine chain (ESC). Geomorphological
investigations were performed to identify the surficial traces of recent
fault activity, generally represented by gentle scarps connecting
uplifted palaeolandscapes of Quaternary age with the flat and lower
areas of the Venetian and Friulian plains. Surficial and subsurficial
data (the latter from reflection seismic profiles) available for the
investigated faults indicate that the thrusts have been responsible for
the displacement of the entire wedge of Quaternary deposits. In the
western sector of the investigated area, the six recognized fault
segments represent portions of a 100-km-long thrust system, at the
boundary between the Alpine relief and the plain areas. In the eastern
sector, active tectonics is the result of parallel thrust segments,
located both in the Alpine mountainous area and in the Friulian plain.
The 3-D geometry of the active thrust segments has been derived from new
structural surficial surveys and the interpretation of reflection
seismic profiles for a total length of 1700 km. On this basis, we
defined the geometry of 10 seismogenic sources whose dimensions are
consistent with the occurrence of earthquakes with M>= 6. The
comparison between the source geometry and the highest intensity data
point distribution of large historical earthquakes has permitted to make
hypotheses on the association of past seismic events to specific
seismogenic sources. This procedure indicated that no large historical
events can be attributed to three sources (Montello-Conegliano,
Arba-Ragogna, Medea). This may indicate an elapsed time since the last
activation of more than eight centuries, based on the completeness of
the historical catalogues. The available data define, therefore, sources
(and related areas) for which a high level of seismic hazard may be
invoked.
The Montello is an elongated hill about 15 km long and 5 km wide located south of the Venetian Alps front and ~100 km southwest of Gemona, site of the destructive Ms~6, 1976 earthquake sequence. Mio-Pliocene strata in the core of the hill are folded. Seven Quaternary terraces across the western termination of the anticline have also been folded and uplifted. The terraces flank the abandoned Biadene valley, a former course of the Piave river which now flows eastwards along the north side of the hill. Topographic profiles along and transverse to the valley and terraces are used to measure the progressive development of the anticline. Fossil remains and archeological sites dated with 14C suggest that the Biadene paleovalley was abandoned between 14 and 8 ka (11+/-3ka). The successive terraces appear to have been emplaced at the onset of interglacials and interstadials, since about 350 ka. The best fitting terrace ages suggest vertical uplift rates of about 0.5 mm/yr before 172 ka and of about 1 mm/yr after 121 ka. The Montello thus appears to be a growing ramp anticline on top of an active, north dipping thrust that has migrated south of the mountain into the foreland. Modeling the deformation of the terraces as a result of motion on such a thrust ramp requires that it propagated both south and upwards with time but with a constant slip rate (1.8-2 mm/yr). For at least 300 kyr the lateral growth of the anticline kept pushing the course of the Piave river southwestwards, at a rate at first of 10 mm/yr, and then 20 mm/yr. Though the growth rate doubled more than 120 kyr ago, the anticline kept a constant height/length growth ratio (~=20) implying self-similar depth/length growth of the thrust underneath. The clustering of historical earthquakes north of Treviso suggests that the thrust responsible for ongoing folding of the Montello slipped seismically three times (778, 1268, 1859 A.D.; intensity I>=VIII) in the last 2000 years, with events of maximum magnitude close to 6 and with average recurrence time between 500 and 1000 years. NW shortening on NE-SW trending thrusts along the Venetian Alps front is compatible with the direction of convergence between Africa and Europe but does not suffice to absorb this convergence.
Palaeoseismological data for the Wasatch and San Andreas fault zones have led to the formulation of the characteristic earthquake model, which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum. Analysis of scarp-derived colluvium in trench exposures across the Wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes. The characteristic earthquake appears to be a fundamental aspect of the behavior of the Wasatch and San Andreas faults and may apply to many other faults as well.-from Authors
Grič Montello je najbrž najbolj tipična morfološka enota krasa, razvitega v konglomeratnih kamninah. Lahko ga štejemo za klasični kras v konglomeratu, primerljivim s klasičnim krasom na apnencu, Tržaškim Krasom. Montello je v tlorisu ovalen, dolg približno 13 km v ZJZ – VSV smeri ter širok okoli 5 km. Razvit je v »montelskem konglomeratu« poznomiocenske starosti (mesinij), ki ga gradijo največ karbonatni prodniki zlepljeni s kalcitnim vezivom, debeline do 2000 m. Montello je oblikovan v cel sistem oblik, nastalih zaradi rečnega uravnavanja in vrezovanja, vidnih na osrednji planoti in sedmih živoskalnih uravnanih teras. Terase so vrezane v pobočje opuščene anticedentne doline. Na rečni uravnavi so se razvile vrtače, večinoma iz grezov pa tudi zaradi točkovnega prenikanja. Vsega skupaj jih je preko 2000. Vrtače na sedmih živoskalnih terasah kažejo različen razvoj in različno velikost glede na starost površja. Kaže, da je bil v začetni fazi morfogeneze vrtač vpliv strukture, to je lezik in razpok, šibak; nasprotno pa je bila poroznost odločujoči dejavnik za razvoj kraškega odtoka.
The Montello hill is, probably, the most typical morphounit between the karsts developed in conglomerate rocks. It may be considered the classical karst of the conglomerates comparable with the Classical Karst of limestones: the Carso of Trieste. The Montello hill consists in an elliptical plan figure, elongated for about13 km in a WSW-ENE direction and a width of about 5 km. The rock unit involved is the “Conglomerato del Montello” of late Miocene age (Messinian), mostly composed by carbonate pebbles bound by a calcitic cement, which is 2000 m thick. The Montello is shaped by a complex system of fluvial planation and incision forms in which are distinguishable a main plateau and a stairs of seven planation rock cut terraces. The terraces are cut in the slope of a dead antecedent valley. On the fluvial planation forms, dolines, mostly of the draw down type but also of the point recharge type, have evolved. In total more than 2000 dolines are present. In the seven rock cut terraces the dolines show different development and dimensions according with the ages of the surfaces. In the first morphogenesis of these dolines and of the caves the control of the plan structures as the bedding surfaces and the fractures seems to have been feeble; on the contrary the porosity of the conglomerate has been a determinant factors for the developmente of the karst drainage.
We consider a large data set of waveforms (5053 recordings for the
horizontal components and 9933 for the vertical) to calibrate a local magnitude scale
valid for northeastern Italy in the hypocentral distance range of 10–250 km. The data
refer to 1096 events occurring in the period January 1995 to December 2002 in the
area between 44.4� and 47.6� N and 10.1� and 15.7� E.
For each available signal, we simulate the corresponding Wood-Anderson seismogram.
Using the geometrical mean of the two horizontal peaks, we simultaneously
estimate the distance attenuation, the station correction terms, and the magnitude of
the events. Estimations are obtained with the standard parametric approach accounting
for the geometrical spreading and the anelastic attenuation, and by using two
different methods of nonparametric regression, based on a stepwise-linear approximation
and on kernel functions, respectively. The nonparametric solutions agree and
show stronger attenuation in the first 70 km than what was found in central California.
Furthermore, a noticeable discontinuity occurs around 100 km, because later phase
arrivals. Such discontinuity is not fitted well by the parametric curve.
We investigate the effect of magnitude-dependent attenuation on magnitude estimation.
We also account for the bias induced by data truncation (i.e., data loss due
to the limited dynamics of the instruments). The analysis shows that at short distances
the standard, magnitude-independent attenuation model underestimates high magnitudes
(e.g., by 0.49 units at 10 km for magnitude 5.5) and overestimates low magnitudes
(e.g., by 0.17 units at 10 km for magnitude 1.5, 0.34 units if we extrapolate
the relation down to magnitude 0.5).
Finally, various factors suggest one should adopt the solution proposed in the
literature to redefine the ML scale such that ML 3 corresponds to 10 mm of motion
on a Wood-Anderson instrument at 17 km hypocentral distance.
Il presente lavoro ha raccolto in modo sistematico i dati di base sismologici e sismotettonici della Regione Veneto, una delle regioni dell’Italia nord-orientale per le quali l’Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) fornisce il servizio di monitoraggio e allarme sismico alla Protezione Civile Regionale. Dalla loro revisione critica ed analisi è stata realizzata una suddivisione del territorio in distretti sismici, ovvero areali caratterizzati da elementi sismologico- sismogenici comuni. Questa zonazione ha uno scopo prevalentemente operativo; la sintesi dei dati disponibili consente una visione di insieme sullo stato delle conoscenze della sismogenesi in questo settore delle Alpi, mentre l’analisi dettagliata delle caratteristiche dei distretti è uno strumento rapido di consultazione in caso di evento sismico, utile sia al personale scientifico in servizio di reperibilità al dipartimento Centro Ricerche Sismologiche di OGS, sia alle autorità deputate ad intervenire sul territorio. Dopo una presentazione dei dati di base analizzati (cap. 2) e dei criteri metodologici utilizzati per analizzare la sismicità (cap. 3), viene fornita una descrizione specifica per distretto (cap. 4), articolata in diversi punti: la sintesi del contesto geologico-strutturale, la presentazione della sismicità storica e strumentale, e il commento di ulteriori livelli informativi riguardanti le strutture attive, gli effetti sul territorio e la normativa sismica. Il Veneto si conferma una regione dalla sismicità significativa, come documentato dalle informazioni storiche; questo aspetto forse non viene adeguatamente messo in rilievo dal dato strumentale disponibile dal 1977, e dalla normativa sismica vigente. Terremoti al di sopra della soglia di percezione hanno interessato un’ampia fascia circa corrispondente alle Prealpi Venete, laddove vi sono maggiori indizi geomorfologici di una deformazione in atto. Non trascurabile, seppure poco nota e di più difficile investigazione, è l’attività di strutture sepolte nella pianura veneta, sia nel settore orientale che in quello occidentale. Nonostante in vaste porzioni del territorio regionale veneto il monitoraggio sismico sia stato, negli ultimi 30-40 anni, disomogeneo e talvolta discontinuo, i database regionali di OGS rappresentano la fonte di dati più omogenea, per l’analisi della sismicità in quest’area. L’installazione di nuove stazioni in aree del Veneto precedentemente poco coperte dal monitoraggio, e l’elaborazione congiunta da parte di OGS dei dati di stazioni sismometriche appartenenti anche ad altre reti hanno notevolmente migliorato negli ultimi anni la capacità di detezione di eventi al di sotto della soglia di percezione. Nella seconda metà del 2011 infine, durante la revisione di questo lavoro, sono avvenuti alcuni eventi fra i più rilevanti del periodo strumentale per l’area del Veneto; essi sono stati citati nella descrizione analitica, pur non essendo concluse le elaborazioni del dato sismologico; queste analisi ed ulteriori studi mirati di carattere multidisclipinare porteranno presumibilmente significativi miglioramenti al quadro conoscitivo dell’area. L’informazione sismologica qui raccolta è confluita nella realizzazione di archivi elettronici, la cui consultazione dinamica è attualmente in fase di implementazione sul sito istituzionale di OGS dedicato alla sismologia in tempo reale (http://rts.crs.inogs.it).
In this paper we gather and review seismological database and seismotectonic literature for one of the north-eastern Italian regions to which OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) provides seismic monitoring and alarm system, the Veneto region. We subdivide the region into 9 seismic districts (Fig. 1), according to some common criteria about seismogenic processes, or data availability. This zonation has a basic operational purpose: it helps the personnel of the Centro Ricerche Sismologiche (CRS) department involved in the rapid availability service, in having an updated and technical overview of the earthquake space-time distribution, and a more detailed description about the main events of the past and about the available knowledge of potential seismogenic sources. This state- of-the-art is a quick manual set up for the local authorities too, as the Regional Civil Defence system is charged to intervene in case of potentially damaging earthquakes. In chapter 2 we describe the dataset available and the ones we used: the data are described separately by historical database (par. 2.1), instrumental archives (par. 2.2), seismogenic sources (par. 2.3), and seismic hazard and regulation (par. 2.4), taking into account the most updated and reliable sources available at the time of the analysis (mid 2011); a synthetic geological and structural framework of eastern Southern Alps and northern Apennines is given as well in par. 2.5, based on literature data only. In chapter 3 some methodological considerations about data quality are given, in order to compile a reference dataset and to represent/analyze the seismicity. Heterogeneous data completeness and magnitude estimates are the main problems pertaining the national and regional instrumental dataset; as no authoritative region is set up for different data providers in north-eastern Italy (from 1977 OGS, but then Istituto Nazionale di Geofisica e Vulcanologia - INGV and Provincia Autonoma di Trento - PAT, with their independent stations and/or data processing), a composition of different datasets is suggested in Table 3.1 for two districts (Giudicarie and Pianura Veneto Ovest) that fall in marginal position with respect to the bulk of OGS monitoring system. Nevertheless, some mislocations, omissions or questionable differences in location parameters have been detected; they have been tracked in the description of individual districts. Chapter 4 describes separately each district, following a common scheme (structural and geological context, historical and instrumental seismicity, neotectonic and active sources, damaging effects and seismic regulation). The Veneto region confirms to be a mid-to-high seismic region, like documented by the historical records. Instrumental data are available since 1977, but their completeness is strongly heterogeneous in time and space; the seismicity pictures of the last decades should take this fact into account. Similarly, many Veneto municipalities exhibit a seismic protection deficit, as they entered in seismic regulation in 2003 only. Earthquakes above the perception threshold occur along a NE-SW wide stripe of mountain-to-plain transition in the Southern Alps, and along the last trait of the Po river. In the Venetian Prealps there are several geomorphological signatures of active deformation, but rates and geometries of potential sources are in many cases still doubtful, or controversial; similarly, the comprehension of mechanisms and activity rates of seismogenic sources buried above thick alluvial deposits, in the lower plain, is tricky. Even if the seismometric monitoring of the Veneto region performed by OGS since 1977 has not been constant in time and coverage, the regional OGS database of instrumental seismicity is by far the most homogeneous and reliable dataset available, for all but the two districts on the westward border of the Lombardia region, and Emilia Romagna region southwards; in these areas, a manual revision of earthquake location is needed by integrating original phases of different seismometric networks, and by common data processing in earthquake location and magnitude assignment. The new seismometric stations installed in the Veneto region during the last 5 years, in the frame of the agreements between Protezione Civile Regionale and OGS, and the uniform processing of data belonging to other networks (the PAT network, and some INGV stations) have increased the detection capability and location quality of small earthquakes. Lastly, some districts (namely Lessini-Schio, Pedemontana Sud and Pianura Veneto Ovest) have been affected in the second half of 2011, by some of the most important earthquakes (widely felt, till to sporadic damages) ever experienced during the modern instrumental period: preliminary comments on this activity have been added to the initial manuscript during its revision, but additional analyses are still ongoing and they will probably increase the level of knowledge about seismogenesis in these areas. The seismological information here gathered and reviewed has been set up into electronic archives in the institutional OGS-CRS web site devoted to real time seismology (http://rts.crs.inogs.it), for dynamic queries under development.
Parole chiave: Veneto, sismogenesi, catalogo terremoti OGS.
Key words: Veneto Region, Italy, seismogenesys, OGS earthquakes catalogue.
The historical and present-day seismicity of the eastern sector of the Veneto region is analyzed and some hypotheses on the seismogenesis are presented. The activity at the intersection of the easternmost Alpine overthrusts with transcurrent lines, is demonstrated and the neotectonic activity is documented. The maximum seismicity appears connected to the recent deformational front. -Authors
[1] We present the first detailed study of earthquake detection capabilities of the Italian National Seismic Network and of the completeness threshold of its earthquake catalog. The network in its present form started operating on 16 April 2005 and is a significant improvement over the previous networks. For our analysis, we employed the PMC method as introduced by Schorlemmer and Woessner (2008). This method does not estimate completeness from earthquake samples as traditional methods, mostly based on the linearity of earthquake size distributions. It derives detection capabilities for each station of the network and synthesizes them into maps of detection probabilities for earthquakes of a given magnitude. Thus, this method avoids the many assumptions about earthquake distributions that traditional methods make. The results show that the Italian National Seismic Network is complete at M = 2.9 for the entire territory excluding the islands of Sardinia, Pantelleria, and Lampedusa. At the M = 2.5 level, which is the reporting threshold level of the Italian Civil Protection, the network may miss events in southern parts of Apulia and the western part of Sicily. The stations are connected through many different telemetry links to the operational data center in Rome. Scenario computations show that no significant drop in completeness occurs if one of the three major links fails, indicating a well-balanced network setup.
Northeastern Italy (NEI), bordering Slovenia and Austria, consists of the Friuli-Venezia Giulia, Veneto, and Trentino-Alto Adige regions. The area includes the Italian part of the southeastern Alps to the north, and the Veneto and Friuli Plains to the south. Together with its neighboring regions of southern Austria and western Slovenia, this is possibly the most tectonically active area of the Alpine Arc in the present age.
The region features the highest seismicity in the Alps, although it can be rated only as moderate level in general terms. According to the CPTI04 catalog (CPTI Working Group, 2004), six earthquakes with MCS intensity greater or equal to IX have struck the area in the last 1,000 years, all with estimated magnitude not exceeding M 6.6 (Figure 1). The last of these occurred in central Friuli on 6 May 1976 ( ML 6.4). Except during the 1976 sequence, magnitude 5.5 or greater earthquakes have occurred only four times in the last century: 1924 and 1928 Tolmezzo, 1936 Cansiglio (Slejko et al. , 1989), and 1998 Bovec, Slovenia, just across the Italian border (Bajc et al. , 2001).
Instrumental seismological observations in NEI started at the end of the 19th century with a few observatories in Italy and the former Hapsburg Empire. Since that time, the reference station for the area is in Trieste (Finetti and Morelli, 1972). In 1931 it was taken over by what is now the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS). It later became part of the World Wide Standardized Seismographic Network (WWSSN, station code TRI-117). Since 1996 the station has been equipped with a Streckeisen STS 1 broadband seismometer managed in collaboration with the Dipartimento di Scienze della Terra dell'Universita di Trieste (DST). It is included in the Mediterranean Very Broadband Seismographic Network (MEDNET) as …
On 6 May 1976, a magnitude 6.4 earthquake struck the Friuli region of northeastern Italy near the towns of Gemona and Venzone. Although it was not as large as some previous earthquakes in Italy, its severe ground motion (up to 0.36 g) affected an area with numerous historical towns, resulting in 989 fatalities and 45,000 people left homeless. At least four other destructive earthquakes with epicentral intensity greater than or equal to IX on the Mercalli‐Cancani‐Sieberg scale have occurred in the Friuli region in the last 5 centuries (1511, 1700, 1794, and 1928) [ Slejko et al. , 1999].
To better understand the seismic hazards of this vulnerable area, a network of continuously operating Global Positioning System (GPS) receivers—the Friuli Regional Deformation Network (FReDNet)—was installed to monitor the regional distribution of crustal deformation (Figure 1).