ALBERT

Description: Mount Etna produced two significant eruptions in 2001 and 2002–2003, which we have analysed using geological, seismic and deformation data. These eruptions showed some similarities, such as the activating of two magmatic plumbing systems (central–lateral and eccentric), but they differed in their triggering mechanisms. While the 2001 eruption was largely the result of the emplacement of a N–S eccentric dike (independent from the central conduits) consistent with E–W regional extension, the 2002–2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano. This is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions. During the months prior to the 2001 eruption, most epicenters were concentrated on the southern flank, at depths of 5–15 km below sea level. During the 4 days before the eruption, earthquake hypocenters migrated to shallower levels (from 5 km bsl. upward) indicating the emplacement of the eccentric dike. This is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements (EDM). In contrast, the months before the 2002–2003 eruption were characterised by shallower seismicity, mainly concentrated along the active faults bordering the slipping flank sector. Flank slip accelerated in September 2002 and a second, more vigorous acceleration of flank slip occurred on 26–27 October 2002, accompanying the opening of eruptive vents. The very short (2 h) seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption. Subsequently, flank slip-deformation extended all over the eastern and southeastern flanks of the volcano, causing serious damage in this sector. The events of 2001–2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics, magma accumulation and eruption, and flank instability. In this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip, which in turn facilitated the 2002–2003 eruption. This sequence of events points to a long-term feedback mechanism between magmatism and flank instability at Etna.

Description: Published

Description: 235-255

Description: partially_open

Description: The island of Pantelleria is an active volcano located in the Sicily Channel (Southern Italy), in the middle of a continental rift system. Since the 1980s the island was periodically surveyed by using geodetic techniques (EDM, levelling, GPS and high precise gravimetry) to monitor the regional and local volcanic dynamics. Gravity data, collected between 1990 and 1998, show short and long wavelength changes due to the combined effect of shallow and deep sources. They reflect, to some degree, the structural setting of the island as delineated by the Bouguer anomaly field, which indicates that the island is broken up into two main basement blocks. The latter are bordered by two lineaments, probably regional faults related to the global geodynamics of the Sicily Channel Rift Zone. Moreover, the inverse correlation between the gravity and altimetric variations suggests that: i) Pantelleria is kinematically divided in two blocks; ii) the observed behaviour is strongly influenced by the geodynamics of the Sicily Channel. A new interpretation of the fully reprocessed data sets is presented, focusing on the spatial–temporal features of the horizontal ground deformation and gravity changes compared to the Bouguer anomaly and altimetric data. This leads to conclude that volcanism on the island has been probably strongly influenced by the global geodynamics of the Sicily Channel, and future eruptions are most likely to occur at the structural boundary separating the two blocks.

Description: Published

Description: 146– 162

Description: reserved

Description: The seismic events caused by human engineering activities are commonly termed as “triggered” and “induced”. This class of earthquakes, though characterized by low-to-moderate magnitude, have significant social and eco- nomical implications since they occur close to the engineering activity responsible for triggering/inducing them and can be felt by the inhabitants living nearby, and may even produce damage. One of the first well-documented examples of induced seismicity was observed in 1932 in Algeria, when a shallow magnitude 3.0 earthquake occurred close to the Oued Fodda Dam. By the continuous global improvement of seismic monitoring networks, numerous other examples of human-induced earthquakes have been identified. Induced earthquakes occur at shallow depths and are related to a number of human activities, such as fluid injection under high pressure (e.g. waste-water disposal in deep wells, hydrofracturing activities in enhanced geothermal systems and oil recovery, shale-gas fracking, natural and CO2 gas storage), hydrocarbon exploitation, groundwater extraction, deep underground mining, large water impoundments and underground nuclear tests. In Italy, induced/triggered seismicity is suspected to have contributed to the disaster of the Vajont dam in 1963. Despite this suspected case and the presence in the Italian territory of a large amount of engineering activities “capable” of inducing seismicity, no extensive researches on this topic have been conducted to date. Hence, in order to improve knowledge and correctly assess the potential hazard at a specific location in the future, here we started a preliminary study on the entire range of engineering activities currently located in Sicily (Southern Italy) which may “potentially” induce seismicity. To this end, we performed: • a preliminary census of all engineering activities located in the study area by collecting all the useful information coming from available on-line catalogues; • a detailed compilation of instrumental and historical seismicity, focal mechanisms solutions, multidisciplinary stress indicators, GPS-based ground deformation field, mapped faults, etc by merging data from on-line catalogues with those reported in literature. Finally, for each individual site, we analysed: i) long-term statistic behaviour of instrumental seismicity (mag- nitude of completeness, seismic release above a threshold magnitude, depth distribution, focal plane solutions); ii) long-term statistic behaviour of historical seismicity (maximum magnitude estimation, recurrence time inter- val, etc); iii) properties and orientation of faults (length, estimated geological slip, kinematics, etc); iv) regional stress (from borehole, seismological and geological observations) and strain (from GPS-based observations) fields.

Description: Unpublished

Description: Vienna (Austria)

Description: 6T. Sismicità indotta e caratterizzazione sismica dei sistemi naturali

Description: open

Description: The area located between Catania and Syracuse (Southeastern Sicily), characterised by the presence of the Simeto-Scordia-Lentini graben, was affected in the past by a strong seismicity as proved by the occurrence of seismic events strong enough to reach the XI degree of the MCS scale. In particular the January 11 th, 1693 (l = XI MCS) earthquake with a magnitude over 7.5 (estimated), caused huge damage and a great loss of human lives. Following the last seismic event which occurred on December 13th, 1990 (Ml = 5.4) which caused heavy damage and many victims in the Catania-Syracuse area, a geodetic Global Positioning System network (GPS) was set up with the aim of monitoring ground movements in one of the Italian areas subjected to high seismic risk, This "pace geodesy technique supplies high precision measurements and represent, a powerful new tool for investigating both regional stress fields and the evolution of local tectonic areas. The GPS network will allow the detection of ground movements with a centimetric accuracy through repeated surveys in time. The results obtained in two surveys carried out il1 1991 al1d 1993, are described in this paper.

Description: JCR Journal

Description: open

Description: The Timpe Fault System is the source of very shallow but destructive earthquakes that affect several towns and villages on the eastern flank of Mt. Etna (Italy). In 1984, several seismic events, and specifically on 19 and 25 October, caused one fatality, 12 injuries and produced serious damage in the Zafferana and Acireale territories. This seismicity was mainly related to the activity of the Fiandaca Fault, one of the structures belonging to the Timpe Fault System. We inverted ground deformation data collected by a geodimeter trilateration network set up in 1977 at a low altitude along the eastern side of the volcano in order to define the Timpe Fault System faulting mechanisms linked to the seismicity in 1984. We have found that in the period May 1980–October 1984, the Fiandaca Fault was affected by a strike-slip and normal dip-slip of about 20.4 and 12.7 cm respectively. This result is kinematically consistent with field observations of the coseismic ground ruptures along the fault but it is notably large compared to displacements estimated by seismicity, then suggesting that most of the slip over the fault plane was aseismic. The results once again confirm how seismicity and its relation with ground ruptures and creep displacement represent a very high hazard to the several towns and villages situated along the Timpe Fault System.

Description: Published

Description: 2443–2453

Description: 1V. Storia e struttura dei sistemi vulcanici

Description: JCR Journal

Description: open

Description: Earthquakes caused by human engineering activities are commonly termed as “triggered” or “induced”. This class of earthquakes, though characterized by low-to-moderate magnitude, have significant social and economical implications since they occur close to the engineering activity responsible for triggering/inducing them and can be felt by the inhabitants living nearby, and may even produce damage. One of the first well-documented examples of induced seismicity was observed in 1932 in Algeria, when a shallow magnitude 3.0 earthquake occurred close to the Oued Fodda Dam (Gupta, 1985). By the continuous global improvement of seismic monitoring networks, numerous other examples of human-induced earthquakes have been identified (see Davies et al., 2013 for an overview). Induced earthquakes occur at shallow depths and are related to a number of human activities, such as fluid injection under high pressure (e.g. waste-water disposal in deep wells, hydrofracturing activities in enhanced geothermal systems and oil recovery, shale-gas fracking, natural and CO2 gas storage), hydrocarbon exploitation, groundwater extraction, deep underground mining, large water impoundments and underground nuclear tests (Davies et al., 2013). Despite the presence in the Sicilian territory of a large amount of engineering activities “potentially capable” of inducing seismicity, no extensive researches on this topic have been conducted to date. Hence, in order to improve our knowledge, and correctly assess the hazard at a specific location in the future, we started a preliminary study on the main engineering activities located on- and off-shore of Sicily (Southern Italy). To this end, in a first step we collected all the useful information coming from available on-line national and regional catalogues. The compiled database includes 46 dams, 598 quarries and 839 oil and gas wells for a total of 1483 engineering activities. Among these, 175 are located along the southern Sicilian coastal off-shore while the remaining 1308 are located inland. As a second step, we performed a detailed compilation of instrumental seismicity striking the investigated area. Continuous seismic monitoring of the whole Italian territory started in the 90s and is currently performed by the National Seismic Network managed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). In addition, monitoring and systematic analysis of seismic activity in eastern Sicily, by means of a dense local network, is performed also by the “Osservatorio Etneo” (INGV-OE), an INGV-branch located in Catania, close to Mt. Etna. Since 1983, earthquakes occurred in the entire Italian territory have been analysed and archived in the catalogue managed by the INGV headquarters in Rome (INGV-CNT; Castello et al., 2005; ISIDe Working Group - INGV, 2010), while since 1999, earthquakes occurred in eastern Sicily have been analysed and archived in the database of the INGV-OE (Alparone et al., 2009; Gruppo Analisi Dati Sismici, 2016). Because the INGV-OE catalogue covers with great details only the eastern sector of Sicily, while the INGV-CNT catalogues, extends back in time since 1983, in order to identify possible prospective effects of the human activities on the seismicity, here we took into account both catalogues. We considered only the seismicity occurred within the first 10 km of the crust because the induced seismicity should be likely confined in the shallower crust. As a final step, in order to identify prospective effects of the human activities on the seismicity, we investigated the spatio-temporal relationships between engineering activities and earthquakes, by adopting a statistic approach aimed to the detection of anomalous seismicity densities. Finally, we identified 46 engineering activities (2 dams, 16 wells and 28 quarries) characterized by anomalous seismicity density. These activities are mainly located in Western Sicily and on the eastern sector of the Hyblean Plateau, while a few number of activities are locate in northern Sicily and on the Island of Vulcano. Currently, we are performing detailed analyses on the nature of the observed seismicity activity in proximity of these engineering activities.

Description: Published

Description: Napoli (Italy)

Description: 6T. Sismicità indotta e caratterizzazione sismica dei sistemi naturali

Description: restricted