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  • 1
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    Seismotectonic analysis of a complex fault system in Italy: the "Garfagnana-North" (Northern Tuscany) line (2007)
    Details
    Publication Date: 2017-04-04
    Description: We present the results obtained combining different techniques to determine the seismotectonic character of the Garfagnana region (northern Tuscany). There, the existence of a rather complex fault system is acknowledged and somewhat mapped, but apart from the geological evidences, very little is known about its extension with depth and the regime. The seismic potential of the system is also well known. The area was characterized, in the past, by destructive earthquakes; in particular a major event (Ms=6.4) struck the Lunigiana-Garfagnana area in September 1920, but many others have been reported. Therefore, the seismicity is under constant monitoring by the national seismic network (RSNC – National Central Seismic Network) and a pool of local stations, belonging to a regional network (RSLG – Regional Seimic network of Lunigiana and Garfagnana). These additional stations account for the lower magnitude seismicity. Such a concentration of seismic stations, and the consequent availability of several seismograms, makes likely to record and localize earthquakes down to a very low magnitude threshold (inferior to Ml = 2.0) with extremely narrow hypocentral parameter errors . Making use of the resulting databases, several analyses were conducted to determine the shape, size, extension with depth of the fault and the associated seismicity. The methodology consists in seismic tomography (1D and 3D velocity models), precise location algorithms NonLinLoc and HypoDD (very constrained and reliable locations) and computation of focal mechanisms (fault orientation and source), all combined with the constraints provided by the geology. The main findings of the study are that the concentration of the recent seismic activity is close to the likely location of the most relevant historical events. In particular the earthquakes are distributed along a plane in the range 0 – 20 km depth dipping 30° NE. All focal mechanisms show a transtensive character.
    Description: Published
    Description: 131-133
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: partially_open
    Keywords: Seismicity ; tomography ; focal mechanism ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Implicazioni sismotettoniche del terremoto di Taggia del 26 Maggio 1831 (2007)
    Details
    Publication Date: 2017-04-04
    Description: Il 26 Maggio 1831, alle ore 10.30, la Liguria occidentale fu interessata da un terremoto che colpì in modo distruttivo 15 paesi ed interessò anche la provincia di Genova, il Piemonte e la Provenza. L’area dei massimi effetti fu localizzata nella parte prossima al mare della valle Argentina, in particolare nei territori dei comuni di Castellaro, Taggia e Bussana, che furono i centri maggiormente danneggiati. In particolare, a Bussana furono distrutte 24 case e 49 vennero demolite poiché pericolanti. A seconda del catalogo considerato, le informazioni macrosismiche disponibili per questo evento sono relative a circa 30 località. Nonostante questo numero non sia in assoluto esiguo, tuttavia appare sottostimato rispetto a quello di altri eventi di caratteristiche simili e periodi contigui, come ad esempio quello del 1854 (86 osservazioni), quello del 1818 (46 siti). Stante l’impossibilità di aumentare il numero di dati a disposizione, e potendo utilizzare solo quelli pubblicati, sono state comunque effettuate una revisione della localizzazione ed un calcolo preliminare delle caratteristiche della sorgente utilizzando il programma Boxer 3.3. I risultati ottenuti conducono alla interpretazione secondo cui l’azimuth della sorgente sismogenetica sarebbe in direzione quasi perpendicolare a quella della faglia Saorge-Taggia.
    Description: Published
    Description: Consiglio Nazionale delle Ricerche, Piazzale Aldo Moro 7, ROMA
    Description: 3.10. Sismologia storica e archeosismologia
    Description: open
    Keywords: Seismoctonics, macroseismic location ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Extended abstract
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  • 3
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    Inferences on active faults at the Southern Alps–Liguria basin junction from accurate analysis of low energy seismicity (2009)
    Elsevier
    Details
    Publication Date: 2017-04-03
    Description: Seismotectonic studies concern themselves with understanding the distribution of earthquakes in space, time, size and style. Therefore, the better these parameters are known, the most correct the association of any seismic event with the faulting structure that caused it will result. The use of accurate location methods is especially required when dealing with very complex areas, where several faulting systems or relatively small seismogenic structures exist. In fact, even though routinely determined epicentres are capable of revealing the rough picture of the seismicity, they are not suitable for studies of the fine structure of the causative fault, as their location uncertainties are often larger than the source dimension itself. In this work the probabilistic approach of the “Non Linear Localization” has been used to compute precise locations for earthquakes occurred in the last twenty years nearby the Saorge–Taggia line, a complex fault system situated in Western Liguria, close to the border between Italy and France. Together with the Breil– Sospel–Monaco and the Peille–Laghet faults, this line is responsible for the seismic activity of the area. The seismotectonic study is completed through a local tomographic study and the analysis of the focal mechanisms computed for an enlarged area. The results show that the seismicity associated with this fault system is confined within the first 10 km depth. Many clusters of seismic events are identified along the Saorge–Taggia line. The existence of a not previously mapped branch perpendicular to the Saorge–Taggia line is also recognized. Although its position may suggest it to be the continuation of the Breil–Sospel–Monaco fault system towards NE, our finding would rather suggest no association with the fault. The overall results confirm the complexity of the area; in particular the hypothesis that the Saorge–Taggia system may represent the eastward limit of a subalpine crustal block comprised within the Nice Arc, the named fault and a thrust front which is supposed to be located 20 km offshore find a confirm in the shallow depth of the seismic events. In addition we propose that the western limit of the block, located along the Nice arc, could be instead shifted where the Peille–Laghet fault lays.
    Description: Published
    Description: 470-479
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: High precision locations ; Focal mechanisms ; Fault geometry ; Western Liguria ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Seismotectonics of a low-deformation area: the central Western Alps (Italy) (2012)
    Details
    Publication Date: 2017-04-04
    Description: This work is based on the integration of detailed field mapping, structural analysis and updated seismological data for the central Western Alps. In this area, three regional, steeply-dipping fault systems seem to be connected to the current seismic activity: the Longitudinal Faults, in the western part, the Transverse Faults, in the central part, and the Col del Lis-Trana Deformation Zone, in the eastern part. Structural and seismological data suggest that since the Late Oligocene, a dextral transtensive regime has been active in this area. The Canavese Line seems to represent the structure that decouples this stress regime, acting inside this sector of the chain, from the transpressive regime that characterizes the adjacent westernmost Po Plain. At a regional scale, this transtensive regime is induced by the coexistence of two driving forces: the counterclockwise rotation of the Adria plate and the body forces acting inside the chain. These two different forces, induced respectively, the dextral and normal components of movement along the major faults bounding the Western Alps. The data fit in a model of dextral transcurrence at the scale of the Western Alps. The data presented in this work contribute to an updated seismic macrozonation of the western Alpine chain, a very populated area where, up to now, only marginal seismotectonic studies have been carried out.
    Description: Published
    Description: 261-281
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: seismotectonics ; recent seismicity ; western Alps ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Seismotectonic investigations in the inner Cottian Alps (Italian Western Alps): (2010)
    Details
    Publication Date: 2017-04-04
    Description: This work integrates the results of recent geological–structural studies with new seismological data for the inner Cottian Alps to investigate the connection between faults and seismicity. The major post-metamorphic tectonic feature of this sector is represented by a N–S structure, named Lis–Trana Deformation Zone (LTZ). Since the Late Oligocene, this structure accommodated right-lateral (Late Oligocene–Early Miocene) and subsequently normal (post-Early Miocene) displacements. In the Pleistocene, the activity of the LTZ seems to have caused the development of lacustrine basins inside the valleys that drain this sector of Western Alps. The present-day seismicity joins the northern part of the LTZ and, southwards, other minor sub-parallel structures. In transversal cross-section hypocentres highlight steep surfaces. Focal mechanisms calculated along this structure show both extensional and strike–slip solutions, mostly with one roughly N–S striking nodal plane. Both sub-horizontal (with NE–SW to ENE–WSW trend) and steeply dipping P axes with N–S to NW–SE sub-horizontal T axes are observed. Even if clear evidence of Quaternary tectonic activity in the area is missing, on the basis of the available seismological and geological data we propose that in the inner Northern Cottian Alps the present-day seismic activity may be connected to the LTZ, interpreted as minor sub-parallel fault strand of the Canavese Line. The kinematics of this structure is consistent with the focal mechanisms calculated in this area. Structural and seismological data indicate that LTZ is active under a bulk dextral–transtensive regime since the late Oligocene in the inner Cottian Alps, in agreement with the data published for the adjacent domain of the chain.
    Description: Published
    Description: 1-16
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Western Alps ; Brittle Tectonics ; Active faults ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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