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![Map of Mt. Etna volcano and main tectonic elements from [34]. TFS: Timpe Faults System; PFS: Pernicana Fault System; TF: Trecastagni Fault; TMF: Tremestieri-Mascalucia Fault; BOF: Belpasso-Ognina Fault; FPF: Fiandaca-Pennisi Fault; SAF: San Gregorio-Acitrezza Fault; SFS: South Fault System; RFS: Ragalna Fault System; SGLP: San Giovanni La Punta. Seismic stations of the permanent (UNI-CT, IIV-CNR, INGV-OE) networks are indicated with black squares and grey and white diamonds, respectively (see text for details). Green star represents the ML = 4.8 earthquake recorded on 26 December 2018. SGR: S. Gregorio seismic station. Pink arrow: direction of sliding. Green square: study area. In the two insets (lower left side), a map of Italy and a schematic structural map of Eastern Sicily.](profile/Sebastiano-Imposa/publication/363773685/figure/fig1/AS:11431281085937973@1663965349628/Map-of-Mt-Etna-volcano-and-main-tectonic-elements-from-34-TFS-Timpe-Faults-System.png)
Map of Mt. Etna volcano and main tectonic elements from [34]. TFS: Timpe Faults System; PFS: Pernicana Fault System; TF: Trecastagni Fault; TMF: Tremestieri-Mascalucia Fault; BOF: Belpasso-Ognina Fault; FPF: Fiandaca-Pennisi Fault; SAF: San Gregorio-Acitrezza Fault; SFS: South Fault System; RFS: Ragalna Fault System; SGLP: San Giovanni La Punta. Seismic stations of the permanent (UNI-CT, IIV-CNR, INGV-OE) networks are indicated with black squares and grey and white diamonds, respectively (see text for details). Green star represents the ML = 4.8 earthquake recorded on 26 December 2018. SGR: S. Gregorio seismic station. Pink arrow: direction of sliding. Green square: study area. In the two insets (lower left side), a map of Italy and a schematic structural map of Eastern Sicily.
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![Figure 1. Map of Mt. Etna volcano and main tectonic elements from [34]....](profile/Sebastiano-Imposa/publication/363773685/figure/fig1/AS:11431281085937973@1663965349628/Map-of-Mt-Etna-volcano-and-main-tectonic-elements-from-34-TFS-Timpe-Faults-System_Q320.jpg)
The Trecastagni Fault (TF) is an important tectonic structure in the middle-lower southern flank of Mt. Etna volcano. It is characterised by evident morphological slopes with normal dip-slip ruptures that directly affect roads and buildings. The TF plays a key role in the complex framework of the volcano dynamics since it represents part of the sou...
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... the dynamic of eastern flank seems to have a key role in triggering volcanic eruptions, e.g., [18][19][20]. The eastern flank dynamics is confined by the Pernicana Fault System (Figure 1; PFS; [20][21][22][23][24][25]), which represents the northern boundary and, to the west, the N-S Ragalna Fault System (RFS; [26]). Conversely, the southeastern boundary is less defined because the slip motion is distributed on different faults that progressively accommodate the sliding motion of the SE-wards sliding sector of the volcano, e.g., [10,11,27]. ...
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... the southeastern boundary is less defined because the slip motion is distributed on different faults that progressively accommodate the sliding motion of the SE-wards sliding sector of the volcano, e.g., [10,11,27]. The South Fault System (SFS; Figure 1) represents one of the southern boundaries and is composed of two main parallel lineaments that include the Belpasso-Ognina and Tremestieri-Mascalucia faults and the San Gregorio and Aci Trezza faults [8,[28][29][30]; (Figure 1). In some places, these faults are characterised by evident morphological slopes [31]. ...
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... the southeastern boundary is less defined because the slip motion is distributed on different faults that progressively accommodate the sliding motion of the SE-wards sliding sector of the volcano, e.g., [10,11,27]. The South Fault System (SFS; Figure 1) represents one of the southern boundaries and is composed of two main parallel lineaments that include the Belpasso-Ognina and Tremestieri-Mascalucia faults and the San Gregorio and Aci Trezza faults [8,[28][29][30]; (Figure 1). In some places, these faults are characterised by evident morphological slopes [31]. ...
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... between the Trecastagni and San Giovanni la Punta villages, before joining the San Gregorio-Aci Trezza fault that also extends off-shore from the volcano [32,33]. The TF is an active structure with a roughly NNW-SSE trend (Figure 1), characterised by morphological escarpments and with a normal kinematic. ...
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... surveys have recently been carried out to investigate the structure and geometry of the TF. In particular, three MASW (multichannel analysis of surface waves) surveys and 41 ambient noise samplings were performed, divided between three alignments crossing the TF (Figures 1 and 2(c1-c3)). ...
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... the late 1970s, a short-period seismic network, comprising five to nine stations, was managed by the University of Catania [37][38][39]. Since 1989, the network was run first by the Istituto Internazionale di Vulcanologia (IIV-CNR; 13 stations), then in 1999 by the Progetto Poseidon (44 stations), and successively, starting from 2001, the INGV-OE network has undergone, in about 20 years, various configurations (Figure 1). In fact, from 2005, the technology of several stations was upgraded from analogic short period 1-component to digital broad-band 3-component, and, at present, the INGV-OE permanent seismic network consists of about 30 stations ( Figure 1). ...
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... 1989, the network was run first by the Istituto Internazionale di Vulcanologia (IIV-CNR; 13 stations), then in 1999 by the Progetto Poseidon (44 stations), and successively, starting from 2001, the INGV-OE network has undergone, in about 20 years, various configurations (Figure 1). In fact, from 2005, the technology of several stations was upgraded from analogic short period 1-component to digital broad-band 3-component, and, at present, the INGV-OE permanent seismic network consists of about 30 stations ( Figure 1). ...
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... the geometry of the INGV-OE seismic network is sparse in the southern sector of volcano, we added a station (SGR) managed by an agreement between the Dipartimento di Scienze Biologiche, Geologiche e Ambientali of the University of Catania and the Municipality of S. Gregorio di Catania. This station SGR, located in San Gregorio di Catania territory, near the Trecastagni Fault, is equipped with a short-period three-component seismometer (Figure 1). We focused on three earthquakes that occurred in the posteruption December 2018 phase. ...
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... comparing results of the November 2009 survey with those of the successive ones, the slip related to the Trecastagni Fault can be detected and followed in time. In this 12-year comparison, a clear jump of about 7-8 cm affected stations across the fault both in southern and northern sides ( Figure 10). Indeed, while all benchmarks lying on the western side of the fault recorded very low variation in their vertical positions with respect to T1 benchmark from November 2009 to September 2021, those lying just east of the structure were affected by a subsidence of several centimetres that gradually decreased towards the east, away from the fault. ...
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... traces intersected the levelling route between benchmarks T5-T6 on the southern side and between the benchmarks T15-T16 on the northern one (Figure 2a). Concerning the time series of the benchmarks crossing the fault (T5-T6 in southern side and T15-T16 in northern side Figure 11), large variations were recorded in the period 2012-2019. Due to the longer time period, vertical displacements are overall more significant than the other comparison but fall within the average rate; however, a comparison with extensometer data suggests that a significant part of these changes is attributable to the February 2019 event. ...
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... ascending/descending interferograms ( Figure 12) map the movements occurring on the whole volcano, along the Pernicana fault to the north, along the Fiandaca fault to the southeast and along the Calcerana fault to the south-west. The comparison of the ascending and descending interferograms evidences a general asymmetric deformation pattern, suggesting a stronger horizontal component of the ground deformation, compatible with a radial ground deformation pattern probably due to an "adjustment" of the volcanic edifice after the huge deformation during the December 2018 dyke intrusion and the Fiandaca earthquake. ...
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... selected two time periods conforming with seismic events during the first February decade. During the first period, from 27 January to 8 February, a ground deformation of about 1 cm was visible along the Trecastagni Fault, localised very close to the ML 2.5 seismic event on 6 February; furthermore, a wider deformation was evident along the S. Gregorio-Acitrezza fault (white arrows in Figure 13), occurring in this short period. In the second 6-day period (from 8 to 14 February), the interferograms detected ground deformation localised northwards along the fault, with respect to the previous period, in accordance with the hypocentral location of the ML 2.4 event on 10 February, but no deformation was associable to the ML 2.9 seismic event. ...
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... the second 6-day period (from 8 to 14 February), the interferograms detected ground deformation localised northwards along the fault, with respect to the previous period, in accordance with the hypocentral location of the ML 2.4 event on 10 February, but no deformation was associable to the ML 2.9 seismic event. In Figure 13, we report the cumulative (18 days) ground deformation image by the DInSAR data. ...
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... during these 40 years, stick-slip seismic activity and slow-slip accelerations along the TF often occur concurrently to (e.g., 1983 and 1985 eruptions) or immediately before (e.g., 2002-2003, 2004-2005 eruptions) or after (2008,2018 eruptions) the main lateral eruptions of the Mt. Etna volcano, as well as during the inflation phases (Figures 1a, 9, 10 and 13). Medium-term deformation of the TF has already been well characterized by Time Series derived from Advanced SAR data analyses by [28,30] and summarized in the database provided by [34], together with all geometric and kinematic information from all available literature. ...
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... May 2019, levelling measured almost 5 cm of vertical displacement with respect to the previous measurement made in 2012; this is a very high value, mainly imputable to the February 2019 episode (see Figure 11), considering that the structure has an estimated slip rate of about 3-4 mm/year [8]. ...
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... evidence and spatial detail are provided by InSAR data (Figure 13): the interferograms highlight a northwards propagation of the dislocation along the TF between the 2 and 8 and 8 and 14 February "windows", in accordance with the extensometers' delayed accelerations. ...
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... note, starting from January 2019, the temporal distribution of the most energetic events follows an "anticlockwise" rotation from the south-western flank to the southern and eastern sectors of the volcano [24]. During the 2018 flank eruption, the magma intrusion caused significant ground deformation [91] and redistribution of stress on the neighbouring faults (Figure 12). According to Alparone et al., 2020 [24], the temporal anticlockwise distribution, from the south-western flank (Rift W) to the southern and eastern sectors of the volcano, of the most powerful events (H < 6 km) after the eruptive episode, could delimit the margins of the unstable sector [24]. ...
Citations
... The seismicity and infrasound signals are monitored through permanent seismic and infrasonic networks. The former currently consists of about 30 digital broadband 3-component stations and the second one of 10 sensors co-located with the seismic ones [23,57]. The strain changes related to the SEC's lava fountains are measured through four borehole dilatometers [58]. ...
On 21 May 2023, a hidden eruption occurred at the Southeast Crater (SEC) of Etna (Italy); indeed, bad weather prevented its direct and remote observation. Tephra fell toward the southwest, and two lava flows propagated along the SEC’s southern and eastern flanks. The monitoring system of the Istituto Nazionale di Geofisica e Vulcanologia testified to its occurrence. We analyzed the seismic and infrasound signals to constrain the temporal evolution of the fountain, which lasted about 5 h. We finally reached Etna’s summit two weeks later and found an unexpected pyroclastic density current (PDC) deposit covering the southern lava flow at its middle portion. We performed unoccupied aerial system and field surveys to reconstruct in 3D the SEC, lava flows, and PDC deposits and to collect some samples. The data allowed for detailed mapping, quantification, and characterization of the products. The resulting lava flows and PDC deposit volumes were (1.54 ± 0.47) × 10⁶ m³ and (1.30 ± 0.26) × 10⁵ m³, respectively. We also analyzed ground-radar and satellite data to evaluate that the plume height ranges between 10 and 15 km. This work is a comprehensive analysis of the fieldwork, UAS, volcanic tremor, infrasound, radar, and satellite data. Our results increase awareness of the volcanic activity and potential dangers for visitors to Etna’s summit area.
... These two borehole stations were chosen on the basis of their proximity to the eruptive vents and availability of data throughout the whole period. At present, the seismic network consists of about 30 digital stations (Alparone et al., 2022). For our purposes, we have chosen four of them, namely EMFO, EMFS, ESVO and ECPN (Fig. 1), following the same criteria adopted for the tilt stations. ...
Mt. Etna exhibited 62 lava fountaining events between December 13, 2020 and February 21, 2022. We analyzed tilt deformations and volcanic tremor amplitude time series, to characterize both eruptions and the preceding preparatory phases in terms of magnitude and speed of development of the volcanic phenomena, as well as to reconstruct the processes that took place inside the plumbing system and drove this intense period of activity. Based on deflation amplitudes associated with lava fountains and according with other retrieved parameters (i.e., magnitude of inflations, inflation and deflation velocities and volcanic tremor amplitudes), three periods have been distinguished. Period I displays higher values of all the aforementioned parameters, interpreted as conspicuous volumes of volatile-rich magma transferred towards the surface. Period II shows lower values evidencing lack of important new injections of magma from depth, whereas period III reveals a general increasing trend possibly related to gas flushing from magma residing in deeper portions of the plumbing system. Detailed elaborations of tilt signals allowed the identification of short-lived inflations accompanying the early stages of lava fountains during period II. Our results reveal significant correlations between amplitude and velocity of tilt and volcanic tremor signals associated with lava fountains and evidence the crucial role of gas in the inflation-deflation cycles.
... This paragraph is focused on the geological and geotechnical modelling of the damaged areas by the 2018 seismic sequence in the municipality of Trecastagni. The GT_Map, reported in Fig. 4a, has been obtained from the geological and geophysical surveys performed in the areas under consideration and from previous literature studies (Alparone et al. 2022;Azzaro 1999;Catalano et al. 2013;Gambino et al. 2011;Kieffer 1975;Tringali et al. 2022). Content courtesy of Springer Nature, terms of use apply. ...
On 26th December 2018, an earthquake (Mw = 4.9) hits the eastern flank of the Etna volcano (Italy). It was the strongest seismic event among seventy with Mw > 2.5 occurring from 23rd December 2018. After the 2018 seismic sequence, seismic microzonation activities have been conducted for several municipalities located in the Etna area. The paper presents the results of seismic microzonation studies for the municipality of Trecastagni damaged by the 2018 seismic sequence. One important aspect in seismic microzonation studies is the definition of subsoil models derived from geological and geotechnical investigations. In this work, an intense investigation campaign has been carried out to define the subsoil models to be used in local seismic response analyses. A peculiarity of the area is constituted by the presence of shear wave velocity inversions typical of volcanic contexts. Another key aspect in seismic microzonation studies is the selection of the most suitable input motions matching on average a reference spectrum in a defined range of periods. In this study, the acceleration response spectrum prescribed by the Italian seismic code for outcropping rock condition and 475 years return period has been assumed as reference. The results of the site response numerical analyses are presented in terms of elastic acceleration response spectra, amplification functions and amplification factors of spectral acceleration defined according to national guidelines and standards for microzonation studies. Findings have been synthetized into three maps representing the amplification factors computed within three ranges of periods. In order to establish an absolute ranking of seismic hazard, a new methodology has been applied by a synthetic damage-constrained parameter (called HSM) whose classification is based on the correlation with the European Macroseismic intensity Scale. Finally, a damage grade map has been developed for a seismically homogeneous microzone based on the macroseismic intensities and the vulnerability classes of the buildings encountered in the area. This study highlights the importance of the HSM parameter in developing emergency planning and mitigation policies.
... The permanent seismic network located on Mt. Etna consists of about 30 digital broadband 3-component stations [29]. The February 6, 2023, M = 7 8 and M = 7 5 seismic events had been recorded by all the stations about 4 minutes later (01 : 21 : 30 UTC and 10 : 28 : 30 UTC, respectively) with respect to origin time with very high amplitudes. ...
On February 6, 2023, at 01 : 17 UTC, a M = 7.8 earthquake struck the southern area of Turkey near Gaziantep town and was followed by a second earthquake of M = 7.5 at 10 : 24 UTC with the epicenter in Elbistan city. Both events were associated with the Anatolian Fault System and have claimed over 50,000 victims, as reported by the Disaster and Emergency Management Authority, and caused serious damage in the regions of southern Turkey and northern Syria. Seismic waves related to strong Turkey earthquakes have been recorded both by seismic stations throughout the globe and on other devices such as the ground deformation (GNSS, strainmeters, or tiltmeters) networks. In this paper, we show and analyze the earthquake signals recorded by bore-hole tilt stations that monitor seismic and volcanic activities at Mt. Etna. Tilt stations showed very large variations, despite their distance from the epicenter (approximately 1950 km) with a period between 10 and 25 seconds. We compared tilt and seismic data for a co–located station evidencing a very similar waveform that highlight how tiltmeters respond to translational acceleration rather than ground tilt during a teleseism, suggesting that, for waves with this period, they may behave as horizontal seismometers. By using these signals, we evidence the different behaviors of two of the most used models of tiltmeters on volcanoes (Lily and Pinnacle) and how they are useful for instrument calibration.
... Consequently, this approach can lead to inaccuracies in determining the predominant frequency of the microtremor spectrum, making it challenging to estimate the site amplification factor [11]. On the other hand, numerous studies have demonstrated that the microtremor horizontal-to-vertical spectral ratio method (HVSR) effectively eliminates the influence of the vibration source on the site dynamics analysis, resulting in predominant frequencies that are more representative of the actual site frequencies [12][13][14][15][16][17][18][19]. As a consequence, many recent studies have employed the microtremor HVSR method to determine the site characteristic parameters. ...
Microtremor recording tests using an accelerometer were carried out in this paper with the aim of characterizing the effects of seasonally frozen soil on the seismic site response, including the two-direction microtremor spectrum, site predominant frequency, and site amplification factor. The study selected eight typical seasonal permafrost sites in China for site microtremor measurements during both summer and winter seasons. Based on the recorded data, the horizontal and vertical components of the microtremor spectrum, HVSR curves, site predominant frequency, and site amplification factor were calculated. The results showed that seasonally frozen soil increased the predominant frequency of the horizontal component of the microtremor spectrum, while the effect on the vertical component was less noticeable. It indicates that the frozen soil layer has a significant impact on the propagation path and energy dissipation of seismic waves in the horizontal direction. Furthermore, the peak values of the horizontal and vertical components of the microtremor spectrum decreased by 30% and 23%, respectively, due to the presence of seasonally frozen soil. The predominant frequency of the site increased by a maximum of 35% and a minimum of 2.8%, while the amplification factor decreased by a maximum of 38% and a minimum of 11%. Additionally, a relationship between the increased site predominant frequency and the cover thickness was proposed.
... By integrating the data of the H/V spectra with the information on the shear waves velocity distribution, it was possible to reconstruct 2D seismic stratigraphic sections known as impedance contrast sections. These sections show the distribution of H/V spectral ratio amplitude values in the subsoil, allowing identifying any horizontal and vertical variations [43][44][45]. Impedance contrasts are determined by the variation of seismic impedance between different layers defined as the product between the density of the medium and the velocity of the shear waves. This parameter affects the propagation of seismic energy content between layers with different physicomechanical properties. ...
Geophysical surveys are widely used to reconstruct subsoil seismo-stratigraphic structures with a non-invasive approach. In this study the geophysical surveys were carried out with the aim to characterise the San Giorgio Cathedral in Ragusa (Italy) and the area on which it is built from a dynamic point of view. A 3D subsoil model was realised through the integration of two active (i.e., seismic tomography and multichannel analysis of surface waves) and one passive seismic technique (horizontal to vertical spatial ratio). The instrumentation used for the latter method consists of a tromograph (Tromino®), which is also employed for the characterisation of the building, focusing on the façade and the dome, by means of an ambient vibration test, processed through the standard spectral ratio and frequency domain decomposition methods. Integration of the 3D model, showing the distribution of areas with different physicomechanical characteristics, enables identifying anomalies that are likely attributable to the remains of the ancient Byzantine church of San Nicola. Four lower modes mainly involving the two investigated macroelements are identified. The experimental results outline the advantages of the use of the tromograph both for soil and structural characterisation, especially for massive masonry buildings located in areas with high seismic hazard.
... By integrating the data of the H/V spectra with the information on the shear waves velocity distribution, it was possible to reconstruct 2D seismic stratigraphic sections known as impedance contrast sections. These sections show the distribution of H/V spectral ratio amplitude values in the subsoil, allowing identifying any horizontal and vertical variations [43][44][45]. Impedance contrasts are determined by the variation of seismic impedance between different layers defined as the product between the density of the medium and the velocity of the shear waves. This parameter affects the propagation of seismic energy content between layers with different physicomechanical properties. ...
Geophysical surveys are widely used to reconstruct subsoil seismo-stratigraphic structures
with a non-invasive approach. In this study the geophysical surveys were carried out with the
aim to characterise the San Giorgio Cathedral in Ragusa (Italy) and the area on which it is built
from a dynamic point of view. A 3D subsoil model was realised through the integration of two
active (i.e., seismic tomography and multichannel analysis of surface waves) and one passive seismic
technique (horizontal to vertical spatial ratio). The instrumentation used for the latter method
consists of a tromograph (Tromino®), which is also employed for the characterisation of the building,
focusing on the façade and the dome, by means of an ambient vibration test, processed through
the standard spectral ratio and frequency domain decomposition methods. Integration of the 3D
model, showing the distribution of areas with different physicomechanical characteristics, enables
identifying anomalies that are likely attributable to the remains of the ancient Byzantine church of San
Nicola. Four lower modes mainly involving the two investigated macroelements are identified. The
experimental results outline the advantages of the use of the tromograph both for soil and structural
characterisation, especially for massive masonry buildings located in areas with high seismic hazard
Persistent Scatterers Interferometric Synthetic Aperture Radar (PS-InSAR) is an advanced satellite remote sensing technique which allows an effective monitoring of ground movement. In this work, PS-InSAR time series as well as precipitation and temperature time series in a region in Catania, Italy are utilized during 2018-2022, and their possible interconnections with land subsidence/uplift due to groundwater level change are investigated. First, the potential jumps in the displacement time series are removed, and then the Sequential Turning Point Detection (STPD) is applied to estimate the times when the velocity of the displacement time series changes. The results show a significant correlation between the frequency of turning points in displacement time series and precipitation trend change, particularly during the winter season. Furthermore, the Least-Squares Cross Wavelet Analysis (LSCWA) is applied to estimate the coherency and phase delay between the displacement and weather cycles in the time-frequency domain. The annual cycles of displacement and temperature show more coherency than the ones of displacement and precipitation across the study region. The results presented herein are important for infrastructure and water management planning.
