http://hdl.handle.net/2122/191 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/5822 Titolo: Seismic images of an extensional basin, generated at the hangingwall of a low-angle normal fault: the case of the Sansepolcro basin (Central Italy)<br/><br/>Autori: Barchi, M. R.; University of Perugia; Ciaccio, M. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: The study of syntectonic basins, generated at the hanging-wall of regional low-angle detachments, can help to gain a better knowledge of these important and mechanically controversial extensional structures, constraining their kinematics and timing of activity.Seismic reflection images constrain the geometry and internal structure of the Sansepolcro Basin (the northernmost portion of the High Tiber Valley). This basin was generated at the hangingwall of the Altotiberina Fault (AtF), an E-dipping low-angle normal fault, active at least since Late Pliocene, affecting the upper crust of this portion of the Northern Apennines. The dataset analysed consists of 5 seismic reflection lines acquired in the 80s’ by ENI-Agip for oil exploration and a portion of the NVR deep CROP03 profile. The interpretation of the seismic profiles provides a 3-D reconstruction of the basin’s shape and of the sedimentary succession infilling the basin. This consisting of up to 1200 m of fluvial and lacustrine sediments: this succession is much thicker and possibly older than previously hypothesised. The seismic data also image the geometry at depth of the faults driving the basin onset and evolution. The western flank is bordered by a set of E-dipping normal faults, producing the uplifting and tilting of Early to Middle Pleistocene succession along the Anghiari ridge. Along the eastern flank, the sediments are markedly dragged along the SW-dipping Sansepolcro fault. Both NE- and SW-dipping faults splay out from the NE-dipping, low-angle Altotiberina fault. Both AtF and its high-angle splays are still active, as suggested by combined geological and geomorphological evidences: the historical seismicity of the area can be reasonably associated to these faults, however the available data do not constrain a unambiguous association between the single structural elements and the major earthquakes. http://hdl.handle.net/2122/5251 Titolo: Unveiling seismic and density structure beneath the Vrancea seismogenic zone, Romania<br/><br/>Autori: Tondi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Achauer, U.; EOST, Strasbourg - France; Landes, M.; Indiana University, Indiana - USA; Davi', R.; University College Dublin, Dublin - IRELAND; Besutiu, L.; Romanian Academy, Bucharest - Romania<br/><br/>Abstract: The Vrancea seismogenic zone in Romania exhibits an intense intermediate-depthseismicity, confined to a relatively small, roughly cylindrical and elongated region, whoseorigin is still under debate. Our three-dimensional P and S wave velocity and densityimages put additional physical constraints on the existing tectonic models to a depth of200 km. The results appear to substantiate a combination of lithospheric delamination andoceanic subduction. For our analysis, we apply the tomographic inversion method ofsequential integrated inversion (SII) to P and S first arrivals from active source datacollected during the VRANCEA99 and VRANCEA2001 seismic refraction experiments,local earthquake data collected during the Carpathian Arc Lithosphere X-Tomography(CALIXTO) experiment and recent gravity measurements of the studied area. Thereconstructed models, which explain both travel times and gravity data, show a subductingslab which exhibits fast Vp, fast Vs, high density, and a low Vp/Vs ratio consistent withthe cold downgoing plate. We associate intermediate-depth seismicity with the observedsharp lateral Vp/Vs variations presumably generated by contact between the dense andcold slab and the lithospheric mantle in the shallower part or the asthenosphere in thedeeper part. This contrast is particularly evident between 100 and 150 km depth, where themaximum historical seismic energy release is concentrated. Our results indicate thediagnostic power of a combined interpretation of 3-D Vp, Vs, Vp/Vs, and density models.<br/><br/>Descrizione: An edited version of this paper was published by AGU. Copyright (2009) American Geophysical Union http://hdl.handle.net/2122/5109 Titolo: Intrusion of eccentric dikes: The case of the 2001 eruption and its role in the dynamics of Mt. Etna volcano<br/><br/>Autori: Bonforte, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Gambino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia<br/><br/>Abstract: The 2001 eruption represents one of the most studied events both from volcanological and geophysical pointof view on Mt. Etna. This eruption was a crucial event in the recent dynamics of the volcano, marking thepassage from a period (March 1993–June 2001) of moderate stability with slow, continuous flank sliding andcontemporaneous summit eruptions, to a period (July 2001 to present) of dramatically increased flankdeformations and flank eruptions. We show new GPS data and high precision relocation of seismicity inorder to demonstrate the role of the 2001 intrusive phase in this change of the dynamic regime of thevolcano. GPS data consist of two kinematic surveys carried out on 12 July, a few hours before the beginning ofthe seismic swarm, and on 17 July, just after the onset of eruptive activity. A picture of the spatial distributionof the sin-eruptive seismicity has been obtained using the HypoDD relocation algorithm based on thedouble-difference (DD) technique. Modeling of GPS measurements reveals a southward motion of the uppersouthern part of the volcano, driven by a NNW–SSE structure showing mainly left-lateral kinematics. Precisehypocenter location evidences an aseismic zone at about sea level, where the magma upraise wascharacterized by a much higher velocity and an abrupt westward shift, revealing the existence of a weakenedor ductile zone.These results reveal how an intrusion of a dike can severely modify the shallow stress field, triggeringsignificant flank failure. In 2001, the intrusion was driven by a weakened surface, which might correspond toa decollement plane of the portion of the volcano affected by flank instability, inducing an additional stresstestified by GPS measurements and seismic data, which led to an acceleration of the sliding flanks. http://hdl.handle.net/2122/5078 Titolo: Three-dimensional P wave attenuation and velocity upper mantle tomography of the southern Apennines–Calabrian Arc subduction zone<br/><br/>Autori: Monna, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Dahm, T.; Institut für Geophysik, Universität Hamburg, Hamburg, Germany<br/><br/>Abstract: We propose a 3-D crust–upper mantle seismic attenuation (QP) model of the southernApennines–Calabrian Arc subduction zone together with a 3-D velocity (VP) model. TheQP model is calculated from relative t* using the spectral ratio method and the VPfrom traveltime data. The final data set used for the inversion of the VP model consists of2400 traveltime arrivals recorded by 34 short-period stations that are part of the ItalianNational Seismic Network, and for the QP model, 2178 Pn phases recorded by a subset of32 stations. Traveltimes and waveforms come from 272 intermediate-depth Calabrianslab events. This 3-D model of attenuation, together with the 3-D velocity model,improves our knowledge of the slab/mantle wedge structure and can be a starting point indetermining the physical state of the asthenosphere (i.e., its temperature, the presenceof melt and/or fluids) and its relation to volcanism found in the study area. Main featuresof the QP and VP models show that the mantle wedge/slab, in particular, the area ofhighest attenuation, is located in a volume underlying the Marsili Basin. The existence andshape of this main low-QP (and low-VP) anomaly points to slab dehydration andfluid/material flow, a process that may explain the strong geochemical affinities betweenthe subduction-related magmas from Stromboli and Vesuvius. Other interesting featuresin the models are strong lateral variations in QP and VP that are put in relation with knownimportant tectonic structures and volcanic centers in the area. http://hdl.handle.net/2122/5010 Titolo: Carbonatite Melts and Electrical Conductivity in the Asthenosphere<br/><br/>Autori: Gaillard, F.; CNRS/INSU, Université d'Orléans, Université François Rabelais - Tours,; Malki, M.; CEMHTI-CNRS, UPR3079, 1D avenue de la Recherche Scientifique, 45071 Orléans cedex2,; Iacono Marziano, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Pichavant, M.; CNRS/INSU, Université d'Orléans, Université François Rabelais - Tours,; Scaillet, B.; CNRS/INSU, Université d'Orléans, Université François Rabelais - Tours,<br/><br/>Abstract: Electrically conductive regions in the Earth mantle have been interpreted to reflect thepresence of either silicate melt or water dissolved in olivine. On the basis of laboratory measurements we show that molten carbonates have electrical conductivities that are 3 orders of magnitude higher than those of molten silicate and 5 orders of magnitude higher than those of hydrated olivine. High conductivities in the asthenosphere probably indicate the presence of small amounts of carbonate melt in peridotite and can therefore be interpreted in terms of carbon concentration in the upper mantle. We show that the conductivity of the Oceanic asthenosphere can be explained by 0.1 volume % of carbonatite melts on average, which agrees with the CO2 content of Mid Ocean Ridge Basalts. http://hdl.handle.net/2122/4942 Titolo: Simultaneous magma and gas eruptions at three volcanoes in southern Italy: An earthquake trigger?<br/><br/>Autori: Walter, T. R.; Department 2: Physics of the Earth, Helmholtz Centre Potsdam, GFZ German Research Centre for Geoscience, Telegrafenberg, 14473 Potsdam, Germany; Wang, R.; Department 2: Physics of the Earth, Helmholtz Centre Potsdam, GFZ German Research Centre for Geoscience, Telegrafenberg, 14473 Potsdam, Germany; Acocella, V.; Dipartimento Scienze Geologiche, Università Roma Tre, Largo S.L. Murialdo 1, 00146 Rome, Italy; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Zschau, J.; Department 2: Physics of the Earth, Helmholtz Centre Potsdam, GFZ German Research Centre for Geoscience, Telegrafenberg, 14473 Potsdam, Germany<br/><br/>Abstract: In September 2002, a series of tectonic earthquakes occurred north of Sicily, Italy, followed by three events of volcanic unrest within 150 km. On 28 October 2002, Mount Etna erupted; on 3 November 2002, submarine degassing occurred near Panarea Island; and on 28 December 2002, Stromboli Island erupted. All of these events were considered unusual: the Mount Etna northeast-rift eruption was the largest in 55 yr; the Panarea degassing was one of the strongestever detected there; and the Stromboli eruption, which produced a landslide and tsunami, was the largest effusive eruption in 17 yr. Here we investigate the synchronous occurrence of these clustered events, and develop a possible explanatory model. We compute short-term earthquake-induced dynamic strain changes and compare them to long-term tectonic effects.Results suggest that the earthquake-induced strain changes exceeded annual tectonic strains by at least an order of magnitude. This agitation occurred in seconds, and may have induced fluid and gas pressure migration within the already active hydrothermal and magmatic systems. http://hdl.handle.net/2122/4895 Titolo: Sea-floor spreading initiation: constraints from geophysical data of the Thetis Deep, northern Red Sea<br/><br/>Autori: Ligi, M.; CNR-ISMAR Bologna; Bonatti, E.; CNR-ISMAR Bologna; Bortoluzzi, G.; CNR-ISMAR Bologna; Brunelli, D.; Università di Modena, Dipartimento di Scienze della Terra; Caratori Tontini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cipriani, A.; Doherty Earth Observatory, Columbia University,; Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cuffaro, M.; CNR-ISMAR Bologna; Ferrante, V.; CNR-ISMAR Bologna<br/><br/>Abstract: A major step in the "Wilson Cycle" is the splitting of a continent and the birth of a new ocean, with the consequent formation of passive plate margins. The transition from a continental to an oceanic rift can be observed today nowhere better than in the Red Sea/Gulf of Aden system. We have carried out during several years a number of expeditions in the axial portion of the Northern Red Sea, in the region where the northernmost nuclei of axial emplacement of oceanic crust can be observed. High resolution multibeam, magnetics, gravity and multichannel seismic reflection surveys from the Thetis Deep revealed rates and modes of initial pulses of sea floor spreading, velocity of S to N axial propagation of the oceanic rift, evolution of initial MORB-type crust and nature of the mantle thermal anomaly that caused the transition from a continental to an oceanic rift. The Thetis deep is made of three en echelon fault-bounded axial basins that are joined together with axial volcanic ridges and a large number of scattered small central volcanoes. The southern basin shows a strong linear magnetic anomaly corresponding to the axial neo-volcanic zone. Two negative symmetric anomalies identified as Matuyama are present in the southernmost part of this basin, suggesting that the emplacement of oceanic crust at this site started roughly 2.5 Ma, with an average half spreading rate of 6 mm/yr. The central sub-basin is also characterized by a strongly magnetic linear neo- volcanic zone that, however, is flanked only by a small, "vanishing" symmetrical negative anomaly suggesting emplacement of oceanic crust not earlier than about 1 Ma. The northern sub-basin does not show a clearly defined linear neo-volcanic zone although it displays a strong central magnetization suggesting initial emplacement of oceanic crust < 0.7 Ma. This pattern implies a south to north time progression of the initial emplacement of oceanic crust within the Thetis system, with a propagation rate of about 20 mm/yr. Gravity data inversions constrained by seismic data reveal that the oceanic crust extends from the axial neo-volcanic ridges toward the master faults of the axial depression with crustal thickness ranging from 4 to 6 km. The increasing thickness of basaltic crust toward the edges of the basin together with higher degree of melting, inferred by the geochemistry of the basaltic glasses, and higher central magnetization of the northernmost and youngest basin suggest a pulse of faster spreading rate at the onset of sea-floor spreading. http://hdl.handle.net/2122/4894 Titolo: Deformation and eruptions at Mt. Etna (Italy): A lesson from 15 years of observations<br/><br/>Autori: Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Casu, F.; Istituto per il Rilevamento Elettromagnetico dell’Ambiente, CNR, Naples, Italy; Acocella, V.; Dipartimento Scienze Geologiche, Universita` Roma Tre, Rome, Italy; Solaro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Pepe, S.; Istituto per il Rilevamento Elettromagnetico dell’Ambiente, CNR, Naples, Italy; Berardino, P.; Istituto per il Rilevamento Elettromagnetico dell’Ambiente, CNR, Naples, Italy; Sansosti, E.; Istituto per il Rilevamento Elettromagnetico dell’Ambiente, CNR, Naples, Italy; Caltabiano, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Lundgren, P.; Jet Propulsion Laboratory, Pasadena, California, USA<br/><br/>Abstract: Volcanoes deform as a consequence of the rise and storage of magma; once magma reaches a critical pressure, an eruption occurs. However, how the edifice deformationrelates to its eruptive behavior is poorly known. Here, we produce a joint interpretation of spaceborne InSAR deformation measurements and volcanic activity at Mt. Etna (Italy), between 1992 and 2006. We distinguish two volcano-tectonic behaviors. Between 1993 and 2000, Etna inflated with a starting deformation rate of 1 cm yr 1 that progressively reduced with time, nearly vanishing between1998 and 2000; moreover, low-eruptive rate summit eruptions occurred, punctuated by lava fountains. Between 2001 and 2005, Etna deflated, feeding higher-eruptive rateflank eruptions, along with large displacements of the entire East-flank. These two behaviors, we suggest, result from the higher rate of magma stored between 1993 and June 2001, which triggered the emplacement of the dike responsible forthe 2001 and 2002–2003 eruptions. Our results clearly show that the joint interpretation of volcano deformationand stored magma rates may be crucial in identifying impending volcanic eruptions. http://hdl.handle.net/2122/4731 Titolo: RAPPORTO SULLE INDAGINI DI SISMICA A RIFLESSIONE, GRAVIMETRICHE, MAGNETOMETRICHE, MORFOBATIMETRICHE E CAMPIONAMENTO FONDO MARE NELL’ ARCO CALABRO (MAR IONIO) CAMPAGNA CALAMARE08<br/><br/>Autori: Polonia, A.; CNR - ISMAR; Bortoluzzi, G.; CNR - ISMAR; Gasperini, L.; CNR - ISMAR; Ligi, M.; CNR - ISMAR; Carrara, G.; CNR - ISMAR; Cuffaro, M.; CNR - ISMAR; D'Oriano, F.; CNR - ISMAR; Riminucci, F.; CNR - ISMAR; Zittellini, N.; CNR - ISMAR; Torelli, L.; Università di Parma; Capozzi, R.; Università di Bologna; Oppo, D.; Università di Bologna; Viola, I.; Università di Bologna; Minelli, L.; Università di Roma-3; Gallais, F.; Université di Brest; Carmisciano, C.; INGV; Gambetta, M.; INGV; Locritani, M.; INGV; Muccini, F.; INGV; Carone, S.; Istituto Idrografico della Marina; Laterra, A.; Istituto Idrografico della Marina<br/><br/>Abstract: The study of the Calabrian Arc in the Ionian Sea is key to understanding of thegeological processes in the Mediterranean Sea. We present the technical details and results ofcruise CALAMARE08 with N/O Urania during spring 2008. We acquired a large set of geologicaland geophysical data, among them Multichannels Seismic and SBP, magnetometry, gravimetry,swath bathymetry and coring of sea bottom. http://hdl.handle.net/2122/4723 Titolo: Possible causes of arc development in the Apennines, central Italy<br/><br/>Autori: Billi, A.; Dipartimento di Scienze Geologiche, Università “Roma Tre”, Rome, Italy; Tiberti, M. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: In central Italy, geometry, kinematics, and tectonic evolution of the late Neogene Umbrian Arc, which is one of the main thrusts of the northern Apennines, have long been studied. Documented evidence for orogenic curvature includes vertical-axis rotations along both limbs of the arc and a positive orocline test along the entire arc. The curvature’s cause is, however, still unexplained. In this work, we focused our attention on the southern portion of the Umbrian Arc, the so-called Olevano-Antrodoco thrust. We analyze, in particular, gravity and seismic reflection data and consider available paleomagnetic, stratigraphic, structural, and topographic evidence from the central Apennines to infer spatial extent, attitude, and surface effects of a mid-crustal anticlinorium imaged in the CROP-11 deep seismic profile. The anticlinorium has horizontal dimensions of about 50 by 30 km and is located right beneath the Olevano-Antrodoco thrust. Stratigraphic, structural, and topographic evidence suggests that the anticlinorium produced a surface uplift during its growth in early Pliocene times. We propose an evolutionary model in which, during late Neogene time, the Olevano-Antrodoco thrust developed in an out-of-sequence fashion and underwent about 16° of clockwise rotation when the thrust ran into and was then raised and folded by the growinganticlinorium (late Messinian-early Pliocene time). This new model suggests a causal link between mid-crustal folding and surficial orogenic curvature that is consistent with several available data sets from the northern-central Apennines; more evidence is, however, needed to fully test hypothesis. Additionally, due to the occurrence of mid-crustal basement-involved thrusts in other orogens, this model may be a viable mechanism for arc formation elsewhere.