http://hdl.handle.net/2122/55 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/6081 Titolo: Seismotectonic of Southern Apennines from recent passive seismic experiments<br/><br/>Autori: Frepoli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Maggi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cimini, G. B:; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Marchetti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Chiappini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: We used data of local earthquakes collected during two recent passive seismic experiments carried outin southern Italy in order to study the seismotectonic setting of the Lucanian Apennine and the surroundingareas. Based on continuous recordings of the temporary stations we extracted over 15,600waveforms, which were hand-picked along with those recorded by the permanent stations of the Italiannational seismic network obtaining a dense, high-quality dataset of P- and S-arrival times. We examinedthe seismicity occurring in the period 2001–2008 by relocating 566 out of 1047 recorded eventswith magnitudes ML ≥1.5 and computing 162 fault-plane solutions. Earthquakes were relocated using aminimum one-dimensional velocity model previously obtained for the region and a Vp/Vs ratio of 1.83.Background seismicity is concentrated within the upper crust (between 5 and 20km of depth) and it ismostly clustered along the Lucanian Apennine chain axis. A significant feature extracted from this studyrelates to the two E–W trending clusters located in the Potentino and in the Abriola–Pietrapertosa sector(central Lucania region). Hypocentral depths in both clusters are slightly deeper than those observedbeneath the Lucanian Apennine. We suggest that these two seismic features are representative of thetransition from the inner portion of the chain to the external margin characterized by dextral strike-slipkinematics. In the easternmost part of the study area, below the Bradano foredeep and the Apulia foreland,seismicity is generally deeper and more scattered. The sparse seismicity localized in the Sibari Plain,in the offshore area along the northeastern Calabrian coast and in the Taranto Gulf is also investigatedthanks to the new recordings. This seismicity shows hypocenters between 12 and 20km of depth belowthe Sibari Plain and is deeper (foci between 10 and 35km of depth) in the offshore area of the TarantoGulf. 102 well-constrained fault-plane solutions, showing predominantly normal and strike-slip characterwith tensional axes (T-axes) generally NE oriented, were selected for the stress tensor analysis. Weinvestigated stress field orientation inverting focal mechanism belonging to the Lucanian Apennine andthe Pollino Range, both areas characterized by a more concentrated background seismicity. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/6080 Titolo: Eruptive versus non-eruptive behaviour of large calderas: the example of Campi Flegrei caldera (southern Italy)<br/><br/>Autori: Carlino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Somma, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia<br/><br/>Abstract: Caldera eruptions are among the most hazardousof natural phenomena. Many calderas around the world areactive and are characterised by recurrent uplift andsubsidence periods due to the dynamics of their magmareservoirs. These periods of unrest are, in some cases,accompanied by eruptions. At Campi Flegrei caldera (CFc),which is an area characterised by very high volcanic risk,the recurrence of this behaviour has stimulated the study ofthe rock rheology around the magma chamber, in order toestimate the likelihood of an eruption. This study considersdifferent scenarios of shallow crustal behaviour, taking intoaccount the earlier models of CFc ground deformation andcaldera eruptions, and including recent geophysical investigationsof the area. A semi-quantitative evaluation of thedifferent factors that lead to magma storage or to itseruption (such as magma chamber size, wall-rock viscosity,temperature, and regional tectonic strain rate) is reportedhere for elastic and viscoelastic conditions. Considering thelarge magmatic sources of the CFc ignimbrite eruptions(400–2,000 km3) and a wall-rock viscosity between 1018and 1020 Pa s, the conditions for eruptive failure aredifficult to attain. Smaller source dimensions (a few cubickilometres) promote the condition for fracture (eruption)rather than for the flow of wall rock. We also analyse theinfluence of the regional extensional stress regime onmagma storage and eruptions, and the thermal stress as apossible source of caldera uplift. The present study alsoemphasises the difficulty of distinguishing eruption andnon-eruption scenarios at CFc, since an unambiguousmodel that accounts for the rock rheology, magma-sourcedimensions and locations and regional stress field influencesis still lacking. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/6079 Titolo: Array analysis and precise source location of deep tremor in Cascadia<br/><br/>Autori: La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Galluzzo, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Malone, S.; Department of Earth and Space Sciences, University of Washington, USA; McCausland, W.; Cascade Volcano Observatory, U.S. Geological Survey, Vancouver, USA; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia<br/><br/>Abstract: We describe a new method to estimate the S‐P time of tremor‐like signals and itsapplication to the nonvolcanic tremor recorded in July 2004 by three dense arrays inCascadia. The cross correlation between vertical and horizontal components indicates thatvery often the high‐amplitude tremor signal contains sequences of P and S wavescharacterized by constant S‐P times (TS‐P) in the range 3.5–7 s. A detailed observation ofthe three component seismograms stacked over the array stations confirms the presence ofP and S wave sequences. The knowledge of the TS‐P poses a strong constrain on thesource‐array distance, which dramatically reduces the uncertainty on source locationswhen used with more traditional array processing techniques. Data were analyzed usingthe zero lag cross‐correlation technique (ZLCC) to estimate the propagation propertiesof the most correlated phases in the wavefield. Detailed polarization analyses werecomputed using the covariance matrix method in the time domain. Polarization parameters,joint with the results of ZLCC, allows for the discrimination between P and S coherentwaves. Results show that the tremor wavefield is composed mostly by shear waves,although a consistent amount of coherent P waves is often observable. The comparison ofthe back azimuth at the three arrays indicate that the source of deep tremor migrates over awide area, and often many independent sources located far from each other are active atthe same time. The tremor source was located by a probabilistic method that uses theresults of ZLCC, given a velocity model. When available, the inclusion of the TS‐P time inthe location procedure strongly reduces the depth range, with a distribution of hypocentersvery near the subduction interface. This result, significantly different compared withprevious less precise locations, makes the Cascadia nonvolcanic tremor more similar to thenonvolcanic tremor recorded in Japan, at least in cases of measurable TS‐P. Thepolarization azimuth aligned with the slow slip direction and the source located on theplate interface indicate that deep tremor and slow slip are two different manifestations of acommon phenomenon related with the subduction dynamics. Sat, 05 Jun 2010 00:00:00 GMT http://hdl.handle.net/2122/6078 Titolo: Chemical composition of precipitation at Mt. Vesuvius and Vulcano Island, Italy: volcanological and environmental implications<br/><br/>Autori: Madonia, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Liotta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia<br/><br/>Abstract: Natural precipitation and water samples frompassive devices were collected at Mt. Vesuvius and VulcanoIsland, Italy, during the period 2004–2006, in order toinvestigate its possible interactions with fumarolic gases.Evidence of chemical reactions between fumarolic fluidsand rain samples before and after its deposition into thesampling devices was found at Vulcano Island. Very lowpH values (down to 2.5) and significant amounts of chlorineand sulfate (up to 22 mEq/l) were measured at samplingpoints located close to the fumarolic field. In contrast,anthropogenic contributions and/or dissolution of aerosols(both maritime and continental) influence the chemistry ofrainwaters at Mt. Vesuvius, which show inter-annualvariations that are highly consistent with those recorded atthe coastal site at Vulcano Island. Chemistry of watersdirectly exposed to fumarolic fluids may then give usefulinformation about its temporal evolution, holding the signalof the ‘‘maximum’’ chemical event occurred in the meanwhile.In addition, the observation of the health status ofvegetation colonizing the immediate surroundings of thefumarolic fields, due to its strong dependence on theinteractions with these fluids, may work as a possiblebiomarker of volcanic activity. Thu, 01 Jul 2010 00:00:00 GMT http://hdl.handle.net/2122/6077 Titolo: Shear-wave velocity structure at Mt. Etna from inversion of Rayleigh-wave dispersion patterns (2 s < T < 20 s)<br/><br/>Autori: Cristiano, L.; Università degli Studi di Salerno; Petrosino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Saccorotti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Ohrnberger, M.; Institut für Geowissenschaften, Universität Potsdam; Scarpa, R.; Università degli Studi di Salerno<br/><br/>Abstract: In the present study, we investigated the dispersion characteristics ofmedium-to-long period Rayleigh waves (2 s < T < 20 s) using both singlestationtechniques (multiple-filter analysis, and phase-match filter) andmultichannel techniques (horizontal slowness [p] and angular frequency[~] stack, and cross-correlation) to determine the velocity structure forthe Mt. Etna volcano. We applied these techniques to a dataset ofteleseisms, as regional and local earthquakes recorded by two broad-bandseismic arrays installed at Mt. Etna in 2002 and 2005, during two seismicsurveys organized by the Istituto Nazionale di Geofisica e Vulcanologia(INGV), sezione di Napoli. The dispersion curves obtained showed phasevelocities ranging from 1.5 km/s to 4.0 km/s in the frequency band 0.05Hz to 0.45 Hz. We inverted the average phase velocity dispersion curvesusing a non-linear approach, to obtain a set of shear-wave velocity modelswith maximum resolution depths of 25 km to 30 km. Moreover, thepresence of lateral velocity contrasts was checked by dividing the wholearray into seven triangular sub-arrays and inverting the dispersion curvesrelative to each triangle. Thu, 01 Apr 2010 00:00:00 GMT http://hdl.handle.net/2122/6076 Titolo: Present-day stress in the surroundings of 2009 L’Aquila seismic sequence (Italy)<br/><br/>Autori: Mariucci, M. T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Montone, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Pierdominici, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: The axial zone of the Apenninic belt in central Italy is a tectonically active region affectedby post-orogenic Quaternary extension. The present-day stress field is characterized by aminimum horizontal stress (Shmin) ∼ NE–SW oriented, derived mainly from earthquake focalmechanisms and secondarily from borehole breakouts and fault data. The paper describes thecomputation of the Shmin orientation along two deep boreholes located in the vicinity of thearea hit by the 2009 April 6, Mw 6.3 L’Aquila earthquake. The analysed wells show breakoutzones at a depth range between 1.4 and 4.6 km, giving precious information on a depth intervalusually not investigated by any other data. The results show an Shmin N81 ± 22◦ and N74 ± 10◦ oriented for Varoni 1 and Campotosto 1 wells, respectively. The comparison among thebreakouts, the 2009 seismic sequence, the past seismicity and the Quaternary faults indicatesa small rotation of Shmin orientation from ∼ NE, in the southern, to ∼ ENE in the northernsector of the study area, where the wells are located. These differences are linked both to thenatural variations of data and to the orientation of the main tectonic structures varying fromNW–SE in the Abruzzi region to ∼ N–S moving toward the Umbro-Marchean Apennines. Theidentification of constant Shmin orientations with depth derived from all the examined activestress data, confirms the breakouts as reliable stress indicators also for aseismic areas. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/6069 Titolo: BET_VH: exploring the influence of natural uncertainties on long-term hazard from tephra fallout at Campi Flegrei (Italy)<br/><br/>Autori: Selva, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Costa, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Marzocchi, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Sandri, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia<br/><br/>Abstract: In this paper, we explore the effects of theintrinsic uncertainties upon long-term volcanic hazardby analyzing tephra fall hazard at Campi Flegrei, Italy,using the BET_VH model described in Marzocchi et al.(Bull Volcanol, 2010). The results obtained show thatvolcanic hazard based on the weighted average of allpossible eruptive settings (i.e. size classes and vent locations)is significantly different from an analysis basedon a single reference setting, as commonly used involcanic hazard practice. The long-term hazard mapfor tephra fall at Campi Flegrei obtained here accountsfor a wide spectrum of uncertainties which are usuallyneglected, largely reducing the bias intrinsicallyintroduced by the choice of a specific reference setting.We formally develop and apply a general method torecursively integrate simulations from different modelswhich have different characteristics in terms of spatial coverage, resolution and physical details. This outcomeof simulations will be eventually merged with field datathrough the use of the BET_VH model. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/6067 Titolo: CO2 degassing at La Solfatara volcano (Phlegrean Fields): Processes affecting d13C and d18O of soil CO2<br/><br/>Autori: Federico, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Corso, P. P.; Dipartimento di Scienze Fisiche e Astronomiche, Universita` di Palermo.Italy; Fiordilino, E.; Dipartimento di Scienze Fisiche e Astronomiche, Universita` di Palermo,Italy; Cardellini, C.; Dipartimento di Scienze della Terra, Universita` di Perugia,Italy; Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Parello, E.; Dipartimento CFTA, Universita` degli Studi di Palermo, Italy; Pisciotta, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia<br/><br/>Abstract: The soil CO2 degassing is affected by processes of isotope exchange and fractionation during transport across the soil,which can deeply modify the pristine isotope composition. This has been observed in the Solfatara volcano, upon a field surveyof 110 points, where the CO2 flux was measured, together with temperature, CO2 concentration and oxygen and carbonisotopes within the soil. Furthermore, in some selected sites, the measurements were made at different depths, in order to analyzevertical gradients. Oxygen isotope composition appears controlled by exchange with soil water (either meteoric or fumaroliccondensate), due to the fast kinetic of the isotopic equilibrium between CO2 and water. Carbon isotope composition isreliably controlled by transport-driven fractionation, due to the differences in diffusion coefficients between 13C16O2 and12C16O2. We model the processes affecting CO2 transport across the soil in La Solfatara volcano by means of the DustyGas Model applied to a multicomponent system, to evaluate the reciprocal effect on diffusion of involved gases, i.e.12C16O2, 13C16O2, N2 and O2 in our case. Both numerical and simplified analytical solutions of the equations based on theDusty Gas Model are given. The modeling results fit well with the experimental data and put in evidence an isotope fractionationof carbon up to about þ4:4& with respect to the source value in the soil gas. This fractionation is independent from theentity of the CO2 flux, and occurs as long as a concentration gradient exists within the soil. On these grounds, the Dusty GasModel can be applied to whichever diffusing gas mixture to evaluate the extent of chemical and/or isotopic fractionation thatcan affect ascending gases upon diffusion in any geothermal, volcanic or tectonic area. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/6066 Titolo: Carbon dioxide diffuse emission from the soil: ten years of observations at Vesuvio and Campi Flegrei (Pozzuoli), and linkages with volcanic activity<br/><br/>Autori: Granieri, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Avino, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia<br/><br/>Abstract: Carbon dioxide flux from the soil is regularlymonitored in selected areas of Vesuvio and Solfatara(Campi Flegrei, Pozzuoli) with the twofold aim of i)monitoring spatial and temporal variations of the degassingprocess and ii) investigating if the surface phenomena couldprovide information about the processes occurring at depth.At present, the surveyed areas include 15 fixed pointsaround the rim of Vesuvio and 71 fixed points in the floorof Solfatara crater. Soil CO2 flux has been measured since1998, at least once a month, in both areas. In addition, twoautomatic permanent stations, located at Vesuvio andSolfatara, measure the CO2 flux and some environmentalparameters that can potentially influence the CO2 diffusedegassing. Series acquired by continuous stations arecharacterized by an annual periodicity that is related tothe typical periodicities of some meteorological parameters.Conversely, series of CO2 flux data arising from periodicmeasurements over the arrays of Vesuvio and Solfatara areless dependent on external factors such as meteorologicalparameters, local soil properties (porosity, hydraulic conductivity)and topographic effects (high or low ground).Therefore we argue that the long-term trend of this signalcontains the “best” possible representation of the endogenoussignal related to the upflow of deep hydrothermalfluids. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/6065 Titolo: Long term variations of the Campi Flegrei (Italy) volcanic system as revealed by the monitoring of hydrothermal activity<br/><br/>Autori: Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Caliro, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Cardellini, C.; Dipartimento di Scienze della Terra, Università di Perugia, Perugia,Italy; Granieri, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Avino, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Baldini, A.; Dipartimento di Scienze della Terra, Università di Perugia, Perugia,Italy; Donnini, M.; Dipartimento di Scienze della Terra, Università di Perugia, Perugia,Italy; Minopoli, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia<br/><br/>Abstract: Long duration time-series of the chemical composition of fumaroles and of soil CO2 flux revealthat important variations in the activity of the Solfatara fumarolic field, the most importanthydrothermal site of Campi Flegrei, occurred in the 2000-2008 period. A continuous increase of theCO2 concentrations, and a general decrease of the CH4 concentrations are interpreted as theconsequence of the increment of the relative amount of magmatic fluids, rich in CO2 and poor inCH4, hosted by the hydrothermal system. Contemporaneously, the H2O-CO2-He-N2 gas systemshows remarkable compositional variations in the samples collected after July 2000 with respect tothe previous ones, indicating the progressive arrival at the surface of a magmatic componentdifferent from that involved in the 1983-84 episode of volcanic unrest (1983-1984 bradyseism).The change starts in 2000 concurrently with the occurrence of relatively deep, long-period seismicevents which were the indicator of the opening of an easy-ascent pathway for the transfer ofmagmatic fluids towards the shallower, brittle domain hosting the hydrothermal system. Since 2000,this magmatic gas source is active and causes ground deformations, seismicity as well as theexpansion of the area affected by soil degassing of deeply derived CO2. Even though the activitywill most probably be limited to the expulsion of large amounts of gases and thermal energy, asobserved in other volcanoes and in the past activity of Campi Flegrei, the behavior of the system inthe future is, at the moment, unpredictable. Fri, 01 Jan 2010 00:00:00 GMT