High-Precision Relative Locations of Two Microearthquake Clusters in Southeastern Sicily, Italy

In November 1999 and in January 2000, two microearthquake swarms occurred in Southeastern Sicily (Italy). They were analytically located in the depth range 17-25 km, some kilometers northward from the buried front of a regional foredeep, below the active thrust zone of the Sicily mountain chain. Their hypocentral distribution showed two distinct clusters, and comparison of the waveforms revealed clearly that the two swarms formed two distinct families of multiplet events. This led us: i) to carry out a precise relocation relative to two chosen master events of the families, and ii) to better define the geometrical structure of the two clusters. The cross-spectral method was applied to obtain precise readings of the wave onsets. SH-wave onsets were used instead of P-waves, as they showed clearer onsets and a good signal-to-noise ratio. Residuals of the relative locations showed small values, no more than several meters on average. The vertical extent of the two relocated clusters was 500 m and 250 m, respectively, while the horizontal extent was 250 m. Hypocenters of the first cluster clearly delineate a NNW trending plane with almost vertical dip, matching one nodal plane of the focal mechanism obtained as a composite solution of all events of the cluster. Given the considerable gap angles, because of unfavorable network geometry with respect to the events, the stability of our results was tested carrying out a Montecarlo experiment. Varying the onset times randomly in the range of 5 ms, a dispersion of the locations less than 10 m in longitude, and less than 50 m both in latitude and depth was found. Similar results were obtained when comparing relocations carried out with different master events. Thus, the overall geometrical characteristics of the clusters were not affected seriously by random errors. Considering the geo-structural framework of the region, together with the location and time evolution of the two clusters, fluids of plutonic origin are suggested as the trigger mechanism

Accurate hypocentre locations in the Middle-Durance Fault Zone, South-Eastern France

A one-dimensional velocity model and station corrections for the Middle-Durance fault zone (south-eastern France) was computed by inverting P-wave arrival times recorded on a local seismic network of 8 stations. A total of 93 local events with a minimum number of 6 P-phases, RMS<0.4 s and a maximum gap of 220° were selected. Comparison with previous earthquake locations shows an improvement for the relocated earthquakes. Tests were carried out to verify the robustness of inversion results in order to corroborate the conclusions drawn from our findings. The obtained minimum 1-D velocity model can be used to improve routine earthquake locations and represents a further step toward more detailed seismotectonic studies in this area of south-eastern France

Terremoti con effetti macrosismici in Sicilia orientale nel periodo Gennaio 2009 - Dicembre 2013

Sono analizzati ed elaborati i dati dei rilievi macrosismici relativi ai terremoti verificatisi in Sicilia nel periodo 2009-2013. Si tratta di eventi che hanno provocato effetti macrosismici di rilievo e/o danneggiamento per la maggior parte localizzati nellâ area etnea, cui si aggiungono alcuni terremoti di magnitudo moderata, legati a sequenze sismiche significative verificatisi nei settori ibleo, peloritano e eoliano. I dati sono stati raccolti e elaborati secondo le procedure operative di prassi adottate in questi casi dal gruppo QUEST (ex-TTC 1.11 â Osservazioni e monitoraggio macrosismico del territorio nazionaleâ ) dellâ INGV, e successivamente parametrizzati secondo gli standard adottati per la compilazione del catalogo CPTI e banca dati macrosismica DBMI (ex-TTC 5.1 â Banche dati e metodi macrosismiciâ )

Geological, seismological and geodetic evidence of active thrustingand folding south of Mt. Etna (eastern Sicily): Revaluation of “seismicefficiency” of the Sicilian Basal Thrust

tGeological studies and morphological analysis, compared with seismological and geodetic data, suggestthat a compressive regime currently occurs at crustal depth in the western sector of Mt. Etna, accommo-dated by shallow thrusting and folding at the front of the chain, south of the volcanic edifice. In particular,a large WSW-ENE trending anticline, interpreted as detachment fold, is growing west and north of Cata-nia city (the Catania anticline). Geological data suggest that during the last 6000 years the frontal foldhas been characterized by uplift rates of ∼6 mm/yr along the hinge, consistent with the interferometricdata (10 mm/yr) recorded in the last 20 years. Moreover, a NNW-SSE oriented axis of compression hasbeen obtained by seismological data, consistent with GPS measurements over the last 20 years whichhave revealed a shortening rate of ∼5 mm/yr along the same direction. Besides the activity related to thevolcanic feeding system, the seismic pattern under the Mt. Etna edifice can be certainly related to theregional tectonics. The compressive stress is converted into elastic accumulation and then in earthquakesalong the ramps beneath the chain, whereas on the frontal area it is accommodated by aseismic defor-mation along an incipient detachment within the clayish foredeep deposits. The high rate of shorteningat the aseismic front of the chain, suggests a greater “seismic efficiency” in correspondence of ramps atthe rear.Published32-412T. Tettonica attivaJCR Journalrestricte

New Geological, seismological and geodetic evidence of active thrusting and folding south of Mt. Etna (eastern Sicily): revaluation of “seismic efficiency” of the Sicilian Basal Thrust

New geological, seismological and geodetic data indicate that a NNW-SSE compressive regime occurs in the southern and western sector of Mt. Etna, accommodated by aseismic folding at the front of the chain. In particular, a large WSW-ENE trending anticline (the Catania anticline) is growing west and north of Catania within a middle-late Pleistocene fold system. For its location, geometry and growth rate, it is consistent with detachment fold models. We exclude that this structure have developed in response to volcanic spreading, as proposed by previous authors. Looking at the earthquakes distribution , an interesting finding is a clear trend of the seismic events deepening from very shallow hypocenters, in the area south of Etna, down to a depth of about 35 km, towards the NNW. Moreover, most of the events are clustered. We computed the focal mechanisms for the major and best recorded earthquakes occurring in the area. One cluster located at few kilometers north-west of the summit craters shows fault mechanisms of the deeper events with nearly horizontal P-axes striking NNW-SSE. A segment of the Sicilian Basal Thrust, located at crustal depth under the northwestern sector of the volcano, could be the seismic source. We propose the occurrence of detachment folding at the chain front, as response of a surface frontal propagation of this regional structure, migrating within the clayish middle-late Pleistocene foredeep deposits or at the top of the buried Hyblean foreland sequence. Geological and morphometric analyses suggest a maximum up warp deformation along the anticline axis of 40 m in the last 6000-7000 yrs, with a vertical slip-rate of 5 - 7 mm/yr. These values are consistent with the growth rate of 9 - 10 mm/yr estimated by interferometric data and the horizontal shortening of 5 mm/yr obtained by GPS measurements. Our analysis confirms that, besides the activity related to the volcanic feeding system, the seismic pattern under Mt. Etna edifice can be certainly related to the regional dynamics. The compressive stress is converted into elastic accumulation and then in earthquakes along the ramps to the rear of the chain, whereas along the frontal detachment it is accommodated by aseismic ductile deformation. In fact, despite the high rates of convergence, the seismicity is moderate at the front of the chain and the “seismic efficiency" of the Sicilian Basal Thrust is greater in correspondence of ramps at the rear, where strong earthquakes can occur.Publishedhttp://www.geoscienze2014.it/1T. Geodinamica e interno della Terraope

Surface and deep strain at Mt. Etna volcano (Sicily, Italy) during the 2003-2004 inflation phase

We carried out a study of the seismicity and ground deformation occurred on Mount Etna volcano after the end of 2002-2003 eruption and before the onset of 2004-2005 eruption, and recorded by the permanent local seismic network run by Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Catania and by the geodetic surveys carried out in July 2003 and July 2004 on the GPS network. We provided a description of seismicity rate and main seismic swarms which occurred during the investigated period. Mostly of the earthquakes are clustered in two main clusters located on the north-eastern (E-W aligned and above the sea level) and south-eastern (NW-SE aligned and from 3 to 8 Km below the sea level) sectors of the volcano. in order to better understand the kinematic processes of the volcano, the 3D relocation were used to compute fault plane solutions and a selected dataset was inverted to determine stress and strain tensors. The focal solutions on the north-eastern sector show clear left-lateral kinematics along an E-W fault plane, in good agreement with the Pernicana fault kinematics. The focal solutions on the south-eastern sector show a main right-lateral kinematics along a NW-SE fault plane evidencing a roughly E-W oriented compression coupled with a N-S extension. Surface ground deformation affecting Mt Etna and measured by GPS surveys highlights a marked inflation during the same period, mainly visible on the western and upper sectors of the volcano; on the contrary, its eastern side shows an exceptionally strong seawards and downwards motion with displacements ranging from 5 up to 10 cm along the coastline. The 2D geodetic strain tensor distribution was calculated on a 1.5 km spaced grid, in order to detail the strain axes orientation above the entire GPS network. The results of the 2D geodetic strain calculation evidenced the very strong extension (mainly along an- ENE-WSW axis) of the summit area that was already considered as the cause of the 2004-2005 eruption; this main ENE-WSW extension continues throughout the eastern flank, but here coupled with a WNW-ESE contraction, meaning a right-lateral shear along a NW-SE oriented fault plane. The opposite deformation of the eastern sector of the volcano, as measured by seismicity and ground deformation has to be interpreted by considering the different depths of the two signals. Seismic activity along the NW-SE alignment is, in fact, located between 3 and 8 km b.s.l. and it is then affected by the very strong additional EW compression induced by the inflating source located by inverting GPS data just westwards and at the same depth. Ground deformation measured by GPS at the surface, on the contrary, is mainly affected by the shallower dynamics of the eastern flank, fastly moving towards East that produces an opposite (extension) E-W strain. It is also meaningful, confirming the decoupling between the surface and deep strain, that all the seismicity of the south-eastern sector lies beneath the sliding plane already modeled by geodetic data for the same time interval and for the 2004-2006 period and also beneath the deeper one previously modeled during the 1993-1998 period when the eastern flank velocity was much slower

Terremoti con effetti macrosismici in Sicilia orientale nel periodo Gennaio 2006 - Dicembre 2008

The macroseismic surveys of earthquakes occurred in Sicily during the time-span 2006-2008, are hereinafter presented. Analysed data mainly concern events located in the volcanic region of Mt. Etna, together with other regional shocks which have produced relevant macroseismic effects in northern and southern Sicily. Data have been collected following the guidelines of the QUEST working group (QUick Earthquake Survey Team, and then processed according to the procedures used for compiling the catalogue and macroseismic database issued in the framework of the TTC (Transversely Coordinated Theme) 5.1 “Banche dati e metodi macrosismici” of INGV

Calibration of input parameters in volcanic areas and an enlarged dataset by stochastic finite-fault simulations

The calibration of input parameters is an important task for stochastic finite-fault simulation in volcanic areas, and we manage this in the framework of the European project UPStrat-MaFa. The stochastic simulation method requires the knowledge of fault geometry, source, crust properties of the region, and local site effects. At first, we focused the present study in the pilot test areas: Mt Vesuvius, Campi Flegrei and Mt Etna. Later, we performed two applications for a large magnitude event in the Azores Islands and the South Iceland regions. A general preliminary database of ground-motion records was collected in the test areas, to set up the empirical laws of the ground-motion parameters. The results of the simulations have been compared with observed waveforms and response spectra, to determine the suitability of the parameters used. The results show good agreement between the observed and simulated time histories and response spectra, thus encouraging further efforts towards quantitative high resolution studies on input parameters.Co-financed by the EU - Civil Protection Financial Instrument, in the framework the European project ”Urban disaster Prevention Strategies using MAcroseismic Fields and FAult Sources (Acronym: UPStrat-MAFA, Grant Agreement N. 23031/2011/613486/SUB/A5). http://ec.europa.eu/echo/funding/cp_projects2011_en.htmPublishedLisbon - Portugal4.1. Metodologie sismologiche per l'ingegneria sismicaope

La sequenza sismica nel versante nord-occidentale dell'Etna del 19-27 Dicembre 2009 : evidenze di ricarica magmatica profonda?

E’ stata analizzata la sequenza sismica che ha interessato il versante nord-occidentale dell’Etna nel periodo 19-27 dicembre 2009 (Fig. 1). Essa è stata caratterizzata da oltre 400 scosse di magnitudo compresa tra 1.0 e 4.8, localizzate ad una profondità tra 20 e 30 km, con un rilevante rilascio energetico, come si osserva dalla distribuzione temporale del numero delle scosse e dell’energia ad esse associata nel tempo (Fig. 2). È interessante notare come l’energia rilasciata durante la sequenza risulti essere quasi il triplo dell’energia del periodo sineruttivo 2008, pur essendo pressoché uguale il numero di scosse registrate. In questo settore dell’area etnea, caratterizzato da sismicità profonda, poco frequente e di modesta energia, la modalità di rilascio sismico della sequenza in oggetto costituisce un elemento di novità. Infatti, più del 50% delle scosse si sono verificate nel corso delle prime 24 ore, come tipicamente osservato nel corso di sciami vulcanici sineruttivi. E’ importante evidenziare che nell’area etnea eventi sismici con profondità focali comprese tra i 10 e i 30 km vengono considerati dei veri e propri “markers” di attività vulcanica (e.g. Puglisi et al., 2001), in quanto si verificano abbastanza regolarmente durante i periodi intra-eruttivi e possono essere messi in relazione con i meccanismi di ricarica magmatica (e.g. Bonaccorso, 2001). Essi sono principalmente localizzati nei settori occidentale e meridionale del vulcano lungo strutture orientate NO-SE e NNO-SSE e, occasionalmente, lungo strutture orientate NE-SO (Patanè et al., 2004). Pertanto è ragionevole ipotizzare che il fenomeno oggetto del presente studio possa essere ricondotto ad una fase di ricarica profonda del sistema magmatico etneo

Calibration of input parameters in volcanic areas and an enlarged dataset by stochastic finite-fault simulations

The calibration of input parameters is an important task for stochastic finite-fault simulation in volcanic areas, and we manage this in the framework of the European project UPStrat-MaFa. The stochastic simulation method requires the knowledge of fault geometry, source, crust properties of the region, and local site effects. At first, we focused the present study in the pilot test areas: Mt Vesuvius, Campi Flegrei and Mt Etna. Later, we performed two applications for a large magnitude event in the Azores Islands and the South Iceland regions. A general preliminary database of ground-motion records was collected in the test areas, to set up the empirical laws of the ground-motion parameters. The results of the simulations have been compared with observed waveforms and response spectra, to determine the suitability of the parameters used. The results show good agreement between the observed and simulated time histories and response spectra, thus encouraging further efforts towards quantitative high resolution studies on input parameters