http://hdl.handle.net/2122/190 Sun, 19 May 2013 16:11:50 GMT 2013-05-19T16:11:50Z http://hdl.handle.net/2122/8056 Title: Upper mantle structure below the European continent: Constraints from surface-wave tomography and GRACE satellite gravity data Authors: Tondi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Schivardi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Molinari, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: We here exploit fundamental mode Rayleigh and Love seismic wave information and the high resolution satellite global gravity model GGM02C to obtain a 1° × 1° 3-D image of: (a) upper-mantle isotropic shear-wave speeds; (b) densities; and (c) density-vS coupling below the European plate (20°N–90°N) (40°W–70°E). The 3-D image of the density-vS coupling provides unprecedented detail of information on the compositional and thermal contributions to density structures. The accurate and high-resolution crustal model allows us to compute a reliable residual topography to understand the dynamic implications of our models. The correlation between residual topography and mantle residual gravity anomalies defines three large-scale regions where upper mantle dynamics produce surface expression: the East European Craton; the eastern side of the Arabian Plate; and the Mediterranean Basin. The effects of mantle convection are also clearly visible at: (1) the Eastern Sirt Embayment; (2) the West African Craton northern margins; (3) the volcanically active region of the Canarian Archipelago; (4) the northern edge of the Central European Volcanic Province; and (5) the Northeastern part of the Atlantic Ocean, between Greenland and Iceland. Strong connections are observed among areas of weak radial anisotropy and areas where the mantle dynamics show surface expression. Although both thermal and additional dependencies have been incorporated into the density model, convective down-welling in the mantle below the East European Craton is required to explain the strong correlation between the estimated negative mantle residual anomalies and the negative residual topography. Tue, 04 Sep 2012 22:00:00 GMT http://hdl.handle.net/2122/8056 2012-09-04T22:00:00Z http://hdl.handle.net/2122/6993 Title: EPcrust : A reference crustal model for the European plate Authors: Molinari, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: We present a new crustal model for the European plate, derived from collection and critical integration of information selected from the literature. The model covers the whole European plate from North Africa to the North Pole (20N - 90N) and from the Mid-Atlantic Ridge to the Urals (40W - 70E). The chosen parameterization represents the crust in three layers (sediments, upper crust and lower crust), and describes the 3D geometry of the interfaces and seismologically-relevant parameters — isotropic P- and S-wave velocity, plus density — with a resolution of 0.5 × 0.5 degrees on a geographical latitude-longitude grid. We selected global and local models, derived from geological assumptions, active seismic experiments, surface-wave studies, noise correlation, receiver functions. Model EPcrust presents significant advantages with respect to previous models: it covers the whole European plate; it is a complete and internally-consistent model (with all the parameters provided, also for the sedimentary layer); it is reproducible; it is easy to update in the future by adding new contributions; and it is available in a convenient digital format. EPcrust could be used to account for crustal structure in seismic wave propagation modeling at continental scale or to compute linearized crustal corrections in continental-scale seismic tomography, gravity studies, dynamic topography and other applications that require a reliable crustal structure. Because of its resolution, our model is not suited for local-scale studies, such as the computation of earthquake scenarios, where more detailed knowledge of the structure is required. We plan to update the model as new data will become available, and possibly improve its resolution for selected areas in the future. Thu, 31 Mar 2011 22:00:00 GMT http://hdl.handle.net/2122/6993 2011-03-31T22:00:00Z http://hdl.handle.net/2122/5849 Title: Carbon-14 as a marker of seismic activity Authors: Mostaccia, D.; Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Berti, C.; Tinazzi, O. Abstract: The principle of carbon-14 dating is well known (1): the content of this radioisotope in a sample of an animal or a plant origin is assessed and the time elapsed from the formation of the organic material to the moment of assessment is calculated comparing the present content of carbon- 14 to that at the time the plant or animal was alive. This last is assumed at equilibrium with the atmospheric concentration of carbon-14, which, in turn, is assumed to have been constant through the ages. Knowing the decay constant of carbon-14, the time elapsed is deduced. Then this calculated age is entered in calibration diagrams that account for the actual variable atmospheric content through the years, to obtain the age of the sample, or more precisely, a time interval in which the age falls. Thus, the main idea behind the technique is that the atmospheric concentration of carbon-14 marked CO2 is essentially constant, or slowly variable, from year to year. To this, one word of caution needs be added: after WW2, and particularly from the 1950s, the concentration of carbon-14 in the atmosphere has become quite erratic due to nuclear weapon tests, and hence this technique is not used for dating samples from that time on.In the present work, the whole carbon-14 idea has been reused in a somewhat different context, and with a different purpose in mind.Afact to be kept in mind is thatCO2 contained in vast amounts within the Earth’s crust beneath the volcanic apparatus, the so-called fossil CO2, either degassed by the mantle or having been formed by metamorphic reactions in the crust, contains no trace of the carbon-14 isotope. Fossil CO2 release is often associated to seismic and volcanic activity: the question may then arise whether, on occasion of such major releases and in the presence of landscape conformation conducive to slow mixing (narrow valley bottoms, canyons, and the like), the carbon-14 contents of local vegetation may be affected by the presence of spent CO2. The Solfatara at Pozzuoli presented both the above-mentioned conditions: it has the required shape and it has endured large releases of fossil CO2 in the early 1980s. It presented itself as an ideal location to test this hypothesis. There are pine trees planted in the 1930s, as part of a reforestation plan: it was possible to select two recently dead trees, one in the Solfatara area and presumably as affected by the CO2 release as could be possible, and the other immediately outside and upwind of the area, constituting an ideal blank. Sections were taken from the two trees and analysed to determine the carbon-14 content of several rings corresponding to the years of interest. In the following sections, the method and the results will be presented and commented upon. Thu, 30 Apr 2009 22:00:00 GMT http://hdl.handle.net/2122/5849 2009-04-30T22:00:00Z http://hdl.handle.net/2122/5292 Title: New geological insights and structural control on fluid circulation in La Fossa cone (Vulcano, Aeolian Islands, Italy) Authors: Barde-Cabusson, S.; Dipartimento di Scienze della Terra, Università Degli Studi di Firenze, Italy; LMV, Université Blaise Pascal, Clermont-Ferrand, France; Finizola, A.; Laboratoire GéoSciences Réunion, UR, IPGP, UMR 7154, Saint-Denis, La Réunion, France; Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy; Revil, A.; Colorado School of Mines, Dept. of Geophysics, Golden, CO, USA; CNRS-LGIT (UMR 5559), University of Savoie, Equipe Volcan, Chambéry, France; Ricci, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Piscitelli, S.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Rizzo, E.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Angeletti, B.; CNRS-CEREGE, Université Paul Cézanne, Aix en Provence, France; Balasco, M.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Bennati, L.; Dept. of Earth & Atmospheric Sciences, Purdue University, West Lafayette, USA; Byrdina, S.; LMV, Université Blaise Pascal, Clermont-Ferrand, France; Equipe de Géomagnétisme, IPGP, UMR 7154, 4, Place Jussieu, 75005 Paris, France; Carzaniga, N.; Dipartimento di Scienze della Terra, Università Degli Studi di Firenze, Italy; Crespy, A.; CNRS-CEREGE, Université Paul Cézanne, Aix en Provence, France; Di Gangi, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Morin, J.; Laboratoire GéoSciences Réunion, UR, IPGP, UMR 7154, Saint-Denis, La Réunion, France; Université Paris 1, Panthéon-Sorbonne, Paris, France; Perrone, A.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Rossi, M.; Dipartimento di Geoscienze, Università di Padova, Italy; Università Milano-Bicocca, Milan, Italy; Roulleau, E.; GEOTOP-UQAM-McGill, Montréal, Canada; Suski, B.; Université de Lausanne (UNIL), Institut de Géophysique, Lausanne, Switzerland; CNRS-CEREGE, Université Paul Cézanne, Aix en Provence, France; Villeneuve, N.; Institut de Recherche pour le Développement, US 140 ESPACE, La Réunion, France Abstract: Electric resistivity tomography (ERT), self-potential (SP), soil CO2 flux, and temperature are used to study the inner structure of La Fossa cone (Vulcano, Aeolian Islands). Nine profiles were performed across the cone with a measurement spacing of 20 m. The crater rims of La Fossa cone are underlined by sharp horizontal resistivity contrasts. SP, CO2 flux, and temperature anomalies underline these boundaries which we interpret as structural limits associated to preferential circulation of fluids. The Pietre Cotte crater and Gran Cratere crater enclose the main hydrothermal system, identified at the centre of the edifice on the base of low electrical resistivity values (b20 Ω m) and strong CO2 degassing, SP, and temperature anomalies. In the periphery, the hydrothermal activity is also visible along structural boundaries such as the Punte Nere, Forgia Vecchia, and Palizzi crater rims and at the base of the cone, on the southern side of the edifice, along a fault attributed to the NW main tectonic trend of the island. Inside the Punte Nere crater, the ERT sections show an electrical resistive body that we interpret as an intrusion or a dome. This magmatic body is reconstructed in 3D using the available ERT profiles. Its shape and position, with respect to the Pietre Cotte crater fault, allows replacing this structure in the chronology of the development of the volcano. It corresponds to a late phase of activity of the Punte Nere edifice. Considering the position of the SP, soil CO2 flux, and temperature maxima and the repartition of conductive zones related to hydrothermal circulation with respect to the main structural features, La Fossa cone could be considered as a relevant example of the strong influence of preexisting structures on hydrothermal fluid circulation at the scale of a volcanic edifice. Wed, 31 Dec 2008 23:00:00 GMT http://hdl.handle.net/2122/5292 2008-12-31T23:00:00Z http://hdl.handle.net/2122/5078 Title: Three-dimensional P wave attenuation and velocity upper mantle tomography of the southern Apennines–Calabrian Arc subduction zone Authors: Monna, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Dahm, T.; Institut für Geophysik, Universität Hamburg, Hamburg, Germany Abstract: We propose a 3-D crust–upper mantle seismic attenuation (QP) model of the southern Apennines–Calabrian Arc subduction zone together with a 3-D velocity (VP) model. The QP model is calculated from relative t* using the spectral ratio method and the VP from traveltime data. The final data set used for the inversion of the VP model consists of 2400 traveltime arrivals recorded by 34 short-period stations that are part of the Italian National Seismic Network, and for the QP model, 2178 Pn phases recorded by a subset of 32 stations. Traveltimes and waveforms come from 272 intermediate-depth Calabrian slab 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 in determining the physical state of the asthenosphere (i.e., its temperature, the presence of melt and/or fluids) and its relation to volcanism found in the study area. Main features of the QP and VP models show that the mantle wedge/slab, in particular, the area of highest attenuation, is located in a volume underlying the Marsili Basin. The existence and shape of this main low-QP (and low-VP) anomaly points to slab dehydration and fluid/material flow, a process that may explain the strong geochemical affinities between the subduction-related magmas from Stromboli and Vesuvius. Other interesting features in the models are strong lateral variations in QP and VP that are put in relation with known important tectonic structures and volcanic centers in the area. Tue, 09 Jun 2009 22:00:00 GMT http://hdl.handle.net/2122/5078 2009-06-09T22:00:00Z http://hdl.handle.net/2122/2865 Title: Composition and thermal structure of the lithosphere beneath the Ethiopian plateau: evidence from mantle xenoliths in basanites, Injibara, Lake Tana Province Authors: Ferrando, S.; Department of Earth Sciences, University of Siena; Frezzotti, M. L.; Department of Earth Sciences, University of Siena; Neumann, E. R.; Physics of Geological Processes, University of Oslo, Norway; De Astis, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Peccerillo, A.; Department of Earth Sciences, University of Perugia; Dereje, A.; Department of Geology and Geophysics,Addis Ababa University, Ethiopia; Gezahegn, Y.; Department of Geology and Geophysics,Addis Ababa University, Ethiopia; Teklewold, A.; Department of Geology and Geophysics,Addis Ababa University, Ethiopia Abstract: Petrographic, minerochemical, and geothermobarometric data are reported for a suite of 19 spinel-lherzolite pargasite xenoliths hosted in a Quaternary basanitic lava flow from 20 the North-Western Ethiopian Plateau (Injibara, Lake Tana Province). Protogranular to 21 porphyroclastic (deformed) rocks show evidence of a modal metasomatism, represented 22 by a Cl-rich pargasitic amphibole, coupled with criptic enrichment in Fe and Al. 23 Equigranular rocks (granular) record a further cryptic metasomatism, represented by 24 enrichment in Fe, Al, Na, and depletion in Ni, Cr and Cl. Some xenoliths (transitional) 25 show intermediate textural and compositional characters, indicating that the granular 26 samples represent an evolution of the deformed ones. All xenoliths give the same P–T 27 equilibration conditions for Opx-Cpx pairs (947–1015 C and 1.3–2 GPa), but in 28 granular samples, recrystallised olivine and spinel record T about 100 C higher. Two 29 distinct metasomatic processes, probably connected with the emplacement of the Afar plume, are proposed. The first one is a pervasive modal metasomatism produced by 2 water-rich fluids. The latter is a non-pervasive cryptic metasomatism, probably con- 3 nected to migration of melts. The comparison among the mantle beneath the Ethiopi- 4 an Volcanic Plateau, the southern Main Ethiopian Rift and the central Main Ethiopian 5 Rift suggests a spatial heterogeneity in mantle processes, during asthenospheric 6 upwelling. Sun, 31 Dec 2006 23:00:00 GMT http://hdl.handle.net/2122/2865 2006-12-31T23:00:00Z http://hdl.handle.net/2122/987 Title: Active tectonics and first paleoseismological results in Faial, Picoand S. Jorge islands (Azores, Portugal) Authors: Madeira, J.; Departamento de Geologia and Laboratório de Tectonofísica e Tectónica Experimental, Faculdade de Ciências da Universidade de Lisboa, Portugal; Brum da Silveira, A.; Departamento de Geologia and Laboratório de Tectonofísica e Tectónica Experimental, Faculdade de Ciências da Universidade de Lisboa, Portugal Abstract: The neotectonics of the islands of Faial, Pico and S. Jorge (Azores) is presented. Preliminary paleoseismology data from trench exposures across three active fault zones (Lomba do Meio, Lagoa do Capitão and Pico do Carvão faults) complement the information. Radiocarbon age constraints of paleoearthquakes suggest clustering of surface rupturing events. Slip rates deduced from paleoseismology analysis range from 0.10 to 0.40 cm/year and validate long-term slip rates obtained by neotectonic studies (using Pleistocene markers). The studied faults allowed a preliminary seismic hazard assessment: magnitudes of the largest paleoearthquakes, determined from slip per event range from Mw = 6.9 to 7.1, and maximum expected magnitudes, estimated from rupture length or rupture area, vary from Mw = 6.4 to 6.8. The former Mw estimates are in closer agreement with the magnitude of the major historic and instrumental seismic events in the archipelago, even though the used empirical relations between magnitude and rupture parameters may not be the most adequate due to the unique tectonic setting of Azores. Tue, 31 Dec 2002 23:00:00 GMT http://hdl.handle.net/2122/987 2002-12-31T23:00:00Z http://hdl.handle.net/2122/617 Title: Towards Inverting Seismic Waveform Data for Temperature and Composition in the Earth's Upper Mantle Authors: Cammarano, F.; Berkeley Seismological Laboratory, University of California Berkeley, CA, US; Romanowicz, B.; Berkeley Seismological Laboratory, University of California Berkeley, CA, US; Stixrude, L.; Department of Geological Sciences, University of Michigan, MI, US; Lithgow-Bertelloni, C.; Department of Geological Sciences, University of Michigan, MI, US Abstract: B: Unraveling the physical state of the upper mantle, including the transition zone, is one of the key factors for understanding the Earth's mantle dynamics. Knowledge of mantle temperature and composition is mainly based on the interpretation of seismological observations based on insights from mineral physics. Despite the progress made to image the 3-D seismic structure of the upper mantle, its interpretation in terms of physical parameters is still challenging and it requires a truly interdisciplinary approach. Due to the better knowledge of the elastic and anelastic properties of mantle minerals at high temperatures and pressures, such an approach is now becoming feasible. We propose a new waveform inversion procedure, based on a formalism previously developed at Berkeley for global elastic and anelastic tomography, and using our existing collection of long-period fundamental and higher mode surface waveforms. Here, we incorporate mineral physics data at an early stage of the process to directly map lateral variations in temperature and composition, using recent estimates of the temperature and composition derivatives of seismic velocities (∂lnV/∂lnT,C). Anelasticity introduces a non-linear dependence of the seismic velocities with temperature throughout the upper mantle, and phase-transitions confer a non-linear character to the compositional derivatives as well, therefore the kernels should be re-computed after each iteration of the inversion. We discuss ways to address the non-linearities, as well as uncertainties in the partial derivatives. In addition to constraining the lateral variations in temperature or composition, the models can have implications on the average structure of the upper mantle. The most-common accepted physical 1-D structure had problems to satisfactorily fit seismic travel time data, requiring a slower TZ to improve the fit. However, these data do not have sufficient coverage (and resolution) in the TZ. A complementary outcome of our models will be to shed light on whether the seismic data require a modification of the physical structure in the transition zone and if the three-dimensional heterogeneity introduces a significant shift of the average physical structure away from adiabatic pyrolite. Mon, 05 Dec 2005 23:00:00 GMT http://hdl.handle.net/2122/617 2005-12-05T23:00:00Z