http://hdl.handle.net/2122/190 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/5849 Titolo: Carbon-14 as a marker of seismic activity<br/><br/>Autori: Mostaccia, D.; Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Berti, C.; Tinazzi, O.<br/><br/>Abstract: The principle of carbon-14 dating is well known (1): the content of this radioisotope in a sampleof an animal or a plant origin is assessed and the time elapsed from the formation of the organicmaterial 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 withthe atmospheric concentration of carbon-14, which, in turn, is assumed to have been constantthrough the ages. Knowing the decay constant of carbon-14, the time elapsed is deduced. Then thiscalculated age is entered in calibration diagrams that account for the actual variable atmosphericcontent through the years, to obtain the age of the sample, or more precisely, a time interval inwhich the age falls. Thus, the main idea behind the technique is that the atmospheric concentrationof carbon-14 marked CO2 is essentially constant, or slowly variable, from year to year. To this, oneword of caution needs be added: after WW2, and particularly from the 1950s, the concentrationof carbon-14 in the atmosphere has become quite erratic due to nuclear weapon tests, and hencethis 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 amountswithin the Earth’s crust beneath the volcanic apparatus, the so-called fossil CO2, either degassedby the mantle or having been formed by metamorphic reactions in the crust, contains no traceof 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 oflandscape 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. TheSolfatara at Pozzuoli presented both the above-mentioned conditions: it has the required shapeand it has endured large releases of fossil CO2 in the early 1980s. It presented itself as an ideallocation to test this hypothesis. There are pine trees planted in the 1930s, as part of a reforestationplan: it was possible to select two recently dead trees, one in the Solfatara area and presumably asaffected by the CO2 release as could be possible, and the other immediately outside and upwindof the area, constituting an ideal blank. Sections were taken from the two trees and analysed todetermine the carbon-14 content of several rings corresponding to the years of interest. In thefollowing sections, the method and the results will be presented and commented upon. Fri, 01 May 2009 00:00:00 GMT http://hdl.handle.net/2122/5292 Titolo: New geological insights and structural control on fluid circulation in La Fossa cone (Vulcano, Aeolian Islands, Italy)<br/><br/>Autori: 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<br/><br/>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 horizontalresistivity 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 lowelectrical 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 faultattributed 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 ofactivity 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 preexistingstructures on hydrothermal fluid circulation at the scale of a volcanic edifice. Thu, 01 Jan 2009 00:00:00 GMT 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. Wed, 10 Jun 2009 00:00:00 GMT http://hdl.handle.net/2122/2865 Titolo: Composition and thermal structure of the lithosphere beneath the Ethiopian plateau: evidence from mantle xenoliths in basanites, Injibara, Lake Tana Province<br/><br/>Autori: 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<br/><br/>Abstract: Petrographic, minerochemical, and geothermobarometric data are reported for a suite of19 spinel-lherzolite pargasite xenoliths hosted in a Quaternary basanitic lava flow from20 the North-Western Ethiopian Plateau (Injibara, Lake Tana Province). Protogranular to21 porphyroclastic (deformed) rocks show evidence of a modal metasomatism, represented22 by a Cl-rich pargasitic amphibole, coupled with criptic enrichment in Fe and Al.23 Equigranular rocks (granular) record a further cryptic metasomatism, represented by24 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 granular26 samples represent an evolution of the deformed ones. All xenoliths give the same P–T27 equilibration conditions for Opx-Cpx pairs (947–1015 C and 1.3–2 GPa), but in28 granular samples, recrystallised olivine and spinel record T about 100 C higher. Two29 distinct metasomatic processes, probably connected with the emplacement of the Afar plume, are proposed. The first one is a pervasive modal metasomatism produced by2 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 Ethiopian5 Rift suggests a spatial heterogeneity in mantle processes, during asthenospheric6 upwelling. Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/2122/987 Titolo: Active tectonics and first paleoseismological results in Faial, Picoand S. Jorge islands (Azores, Portugal)<br/><br/>Autori: 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<br/><br/>Abstract: The neotectonics of the islands of Faial, Pico and S. Jorge (Azores) is presented. Preliminary paleoseismologydata from trench exposures across three active fault zones (Lomba do Meio, Lagoa do Capitão and Pico doCarvão faults) complement the information. Radiocarbon age constraints of paleoearthquakes suggest clusteringof surface rupturing events. Slip rates deduced from paleoseismology analysis range from 0.10 to 0.40 cm/yearand validate long-term slip rates obtained by neotectonic studies (using Pleistocene markers). The studied faultsallowed a preliminary seismic hazard assessment: magnitudes of the largest paleoearthquakes, determined fromslip per event range from Mw = 6.9 to 7.1, and maximum expected magnitudes, estimated from rupture length orrupture area, vary from Mw = 6.4 to 6.8. The former Mw estimates are in closer agreement with the magnitude ofthe major historic and instrumental seismic events in the archipelago, even though the used empirical relationsbetween magnitude and rupture parameters may not be the most adequate due to the unique tectonic setting ofAzores. Wed, 01 Jan 2003 00:00:00 GMT http://hdl.handle.net/2122/617 Titolo: Towards Inverting Seismic Waveform Data for Temperature and Composition in the Earth's Upper Mantle<br/><br/>Autori: 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<br/><br/>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. Tue, 06 Dec 2005 00:00:00 GMT