http://hdl.handle.net/2122/72 Mon, 20 May 2013 01:05:11 GMT 2013-05-20T01:05:11Z http://hdl.handle.net/2122/8530 Title: Modellazione numerica agli elementi finiti per sistemi di faglie potenzialmente sismogenetiche nel territorio italiano, con particolare riferimento alla zona della sequenza sismica umbro-marchigiana del 1997 Authors: Finocchio, Debora; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: Lo scopo fondamentale di questo lavoro è l’applicazione delle tecniche di modellazione numerica per lo studio di sistemi di faglie per verificarne il loro potenziale sismogenetico. Determinare quale faglia merita più attenzione, dal punto di vista del rischio sismico, è una questione attualmente ancora dibattuta. Lo confermano, ad esempio, i terremoti di l’Aquila nel 2009 e di Sumatra nel 2004. Inoltre, secondo uno studio di Wyss et al. (2012), il numero di morti causati dai recenti terremoti è da 100 a 1000 volte più elevato rispetto ai valori predetti dalla mappa mondiale di hazard. Le problematiche riguardanti le mappe di hazard dipendono principalmente dal fatto che sono calcolate mediante cataloghi sismici e dati di tipo geologico. Questo comporta un problema dal punto di vista temporale, in quanto i cataloghi sismici registrano eventi che non coprono un intero ciclo sismico, mentre i dati geologici contengono più eventi registrati, ad esempio, dal rigetto superficiale delle faglie. La questione temporale può essere risolta mediante la modellazione numerica che permette di raccordare i dati a lungo e corto periodo. Infatti, tramite la modellazione numerica, è possibile stimare l’evoluzione di una faglia (in superficie e in profondità) nel periodo intersismico e simulare il caso cosismico. Inoltre la modellazione numerica permette di distinguere le faglie bloccate da quelle sbloccate. Questa distinzione fornisce un elemento utile per valutare la possibilità di un’eventuale rottura. Inoltre è possibile stimare lo stress, la deformazione e la velocità di ricarica di un terremoto. Ho applicato la modellazione numerica a tre aree rappresentative del territorio italiano. Partendo dal centro Italia, ho studiato la faglia a basso angolo dell’Altotiberina e la sua relazione con le faglie di Colfiorito e della Valle Umbra. Ho approfondito lo studio delle faglie a basso angolo, analizzando il caso della faglia di Messina (Sud Italia). Infine, ho studiato l’area esterna del sud Alpino (nord Italia), caratterizzata da un sistema compressivo, che comprende il thrust del Montello ed il thrust di Bassano. Ho modellato numericamente ognuna di queste faglie o sistemi di faglie utilizzando diverse condizioni al contorno e parametri reologici in accordo con l’area di studio. I risultati sono stati confrontati con dati di tipo geodetico, geologico e geofisico. E’ stato possibile verificare che, la modellazione numerica fornisce un ottimo sostegno per la modellazione analogica, contribuendo a dare maggiore completezza al risultato e a simulare alcune proprietà dei materiali con grande precisione. Il risultato di un modello numerico varia principalmente al variare delle condizioni al contorno imposte, quindi dalla geometria, dai parametri reologici, e dal tipo di meccanismo utilizzato per riprodurre la deformazione di un’area. I risultati ottenuti in questo lavoro mostrano che la faglia Altotiberina è completamente bloccata al contrario della faglia di Colfiorito e la faglia della Valle Umbra che si muovono in parte come delle faglie sbloccate. Il campo deformativo dell’area sembra essere guidato da una trazione posta alla base della litosfera. Per quanto riguarda il sistema di thrust del Montello, ho potuto verificare che la porzione bloccata del thrust di Bassano ha un grande potenziale sismogenetico rispetto al thrust del Montello e al thrust antitetico al Montello, che risultano sbloccate. Assumendo che l’ampiezza delle faglie bloccate sia proporzionale all’ampiezza del terremoto, è stato possibile stimare la magnitudo massima attesa per ogni porzione di faglia bloccata, calcolata mediante la modellazione numerica. In particolare, la faglia di Bassano e la faglia Altotiberina sembrano avere un forte potenziale sismogenetico, in quanto potrebbe avere una magnitudo massima attesa di circa 7. Mon, 18 Feb 2013 23:00:00 GMT http://hdl.handle.net/2122/8530 2013-02-18T23:00:00Z http://hdl.handle.net/2122/6166 Title: Time and space domain analysis of gravimetric data Authors: Panepinto, Stefano; Università di Palermo Dip. C.F.T.A. Abstract: The goal of this PhD thesis is to provide an overview on the very different aspects of modern gravimetric research. In particular, this geophysical method is applied here on the one hand as volcano monitoring tool essentially by continuous gravity observations while, on the other hand, for the construction of density-velocity 3D regional models by an integrated inversion procedure of gravimetric and seismic data. The first section concentrates on continuous gravity observation performed at different sites of both Etna and Stromboli volcanoes. The gravity studies allow investigation of mass displacements (magma) and density variations (deep structures) under volcano edifices. Results are presented from high precision gravity measurements fully corrected using tidal and drift optimization programs and having a standard error of few μgal. Tidal analyses results of the treated data sets are also shown and discussed in the first section. Moreover, the simultaneous recording of external parameters (atmospheric pressure, temperature and humidity) is essential as their effects must be removed from the gravity records. The analyses carried out with different processing techniques on several data sets led us to point out the temperature as the responsible parameter for the annual drift present in the records of spring gravimeters. During the end of 2002 one of the gravimetric signals acquired on Mt. Etna showed, in its final residuals reaching a 5 μgal precision, a strong decrease of about 400 μgal in few hours. Correlation between this gravity decrease, on the one hand, and the other geophysical and geochemical signals – in particular the seismic and ground deformation data – as well as the observed summit activities, on the other hand, enable us to qualify the recorded gravity variation as a precursor of the 2002 eruption period. By comparison with simultaneous ground deformation data it is shown that the observed gravity changes are not in general caused by elevation changes but are due to the direct gravitational effect of subsurface movements of matter. Residual gravity changes are interpretable entirely in terms of mass changes in crater conduits and in near-surface dykes lying along know fissure system. Furthermore, the summit activity is consistent with a source at greater depth. Gravity measurements may thus not only contribute to a better understanding of some important features of geodynamics in volcanoes but may also be used directly for the monitoring and the prediction of the eruptions. Section two addresses the unresolved question of the possible interference between tidal forces and volcanism. After the discussion of gravimetric tide results and the determination of tidal parameters, this section is completely devoted to “tidal modulation” of thermometric data acquired at sites very close to the summit active craters of Mt Etna. The intuition that these types of data may contain some geophysical signals related to the tidal stress-strain action, as an evidence of the tidal influence on volcanic processes, comes from the following boundary consideration: since the volcanic areas are characterised by high heat fluxes due to the presence of magma bodies near the surface, taking into account that convection is the major heat transfer mechanism, the tidal strain field within the volcanic edifice could affect this convective process. Some time variations of the efficiency of the convective process should produce corresponding temperature changes observable at shallow depth. The aim of the study is thus to investigate about the presence of a periodic variation due to the main lunar tidal component (M2, tidal period of 12.421 hours). This component is chosen in order to rule out the solar radiation effects. The data set at hand was thus processed with a stacking technique coupled with a wavelet analysis for a preliminary denoising. Through the proposed procedure an anomalous amplitude of the spectral component with a period equal to that of the M2 tidal wave was found. This evidence opens a scientific speculative argument about the interaction between tidal forces and volcanic processes highlighting the possibility, under some particular conditions, of dynamic triggering. The last section deals with a seismo-gravity integrated inversion procedure for the construction of reliable 3D models of the Sicilian area and its surrounding basins. The proposed procedure allows inverting seismic and gravimetric data with a sequential technique to avoid the problematic optimization of assigning relative weights to the different types of data. The proposed procedure underlined the necessity of the different data integration although the seismic problem seemed to be a priori well constrained. Furthermore, it allowed highlighting some velocity and density features that could play a crucial rule for the reconstruction of the geodynamic evolution of the study area. Mon, 29 Mar 2010 22:00:00 GMT http://hdl.handle.net/2122/6166 2010-03-29T22:00:00Z http://hdl.handle.net/2122/5428 Title: Banche dati per le biblioteche di scienze della terra: Georef, Web of Science, Scirus e Google Scholar Authors: Ferrara, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia Abstract: Sin dalla loro introduzione, prima in forma cartacea, poi su supporti informatici, per finire alle versioni elettroniche disponibili via web, le banche dati hanno sempre rappresentato uno strumento fondamentale, indispensabile e non sostituibile della ricerca. Non di meno lo sono per i bibliotecari. Questo presupposto ci deve spingere a valorizzare sempre più il servizio di reference e di information retrieval, visto che gli strumenti a nostra disposizione aumentano di giorno in giorno, sia liberamente fruibili che sotto forma di abbonamenti annuali. Oggi le banche dati stanno varcando l’ambito per cui inizialmente erano state create e stanno per entrare in quello della valutazione della ricerca. In questo lavoro si prendono in considerazione quelle banche dati e quei motori di ricerca specialistici che oramai sono di utilizzo quotidiano in una biblioteca di scienze della terra. In particolare ci si riferirà a: Georef, Web of Science, Scirus e Google Scholar. Il lavoro inizia analizzando storicamente sia le banche dati che i motori di ricerca specialistici, per comprendere la loro natura e le motivazioni alla base della loro creazione. Si procede poi affrontando il tema della qualità del recupero dell’informazione presentata, per finire con l’analisi comparativa delle citazioni ricevute dai record estratti. Mon, 30 Nov 2009 23:00:00 GMT http://hdl.handle.net/2122/5428 2009-11-30T23:00:00Z http://hdl.handle.net/2122/5124 Title: new concept in global tectonics Authors: bozic, zeljko; none Abstract: Nowdays we can easily take for a fact the existance of ancient supercontinent named Pangea.If one just takes a glance at borderlines of modern continents one can conclude,without further argument,that they were once conjoined indeed.But the process of development and the process of disintegration of Pangea still inflames bitter arguments. New concept in global tectonics endorses two-layered lithosphere: Primary Layer: One that covers all of the Earths surface,and Secondary Layer: One that exists on top of Primery layer and consists of Earths continents (originated as Pangea). Therefor,covering aproximetly one quarter of Earths surface. Tue, 30 Jun 2009 22:00:00 GMT http://hdl.handle.net/2122/5124 2009-06-30T22:00:00Z http://hdl.handle.net/2122/4165 Title: EFFECTS OF ENERGETIC SOLAR PARTICLES ON OZONE AND MINOR ATMOSPHERIC COMPONENTS INSIDE THE POLAR REGIONS Authors: Damiani, A.; INAF-IFSI Abstract: Solar activity influences the Earth’s environment, in particular the atmospheric ozone, by the direct output of the e.m. radiation or through the variability of the incoming cosmic ray flux (solar and galactic particles). Especially energetic particles, arising from huge explosions on the Sun’s surface, travel in the interplanetary medium and, if the circumstances were favorable, they could enter the terrestrial atmosphere (driven by the geomagnetic field lines of our planet) and reach the polar cap regions (geomagnetic latitude > 60°). There, they provide additional external energy and are able to produce ionizations, dissociations, dissociative ionizations and excitations phenomena by interacting with the minor constituents. The induced changes are not confined to the ion chemistry but also to the neutral components. In this way a rise of the concentration of HOx and NOx species and the triggering of catalytic cycles which lead to short (hours) and medium (days) term ozone destruction occur. Finally, also no-reactive reservoir species (e.g., HNO3, HCl, HOCl) are involved in these processes and endure large variations. The present thesis highlights the chemical variability of the middle atmosphere during and after some Solar Energetic Particle (SEP) events recorded during the current solar cycle. Special attention has been paid to the relationship between ozone and HOx data (retrieved from the Microwave Limb Sounder of EOS AURA satellite) for four events referred to 2005. The HOx data, recorded for the first time during the intense ionization caused by the SEP flux, have pointed out some features related to these phenomena not wholly captured by the current theoretical models. In addition, they have highlighted that the HOx rise is able to destroy the so-called third ozone peak at the polar latitudes of the winter hemisphere and it occurs also during medium intensity events. Besides, the analyses of January 2005 SEP events have shown that the changes on the hydrogen species leaded to variability in the concentration and partitioning of chlorine family, not discernible in the summer hemisphere. Further, the use of data coming from the HALOE instrument, referred to SEP events occurred in July 2000 and April 2002, has in short confirmed past experimental results. Finally, the study of a little SEP event occurred during May 2003 has pointed out that SEP events are not the unique ionization source inside the polar latitudes during the winter. Fri, 30 Nov 2007 23:00:00 GMT http://hdl.handle.net/2122/4165 2007-11-30T23:00:00Z http://hdl.handle.net/2122/1169 Title: Nature and efficiency of pyroclast generation from porous magma: Insights from field investigations and laboratory experiments Authors: Kueppers, U.; PhD thesis Abstract: Enhanced knowledge of pre- and syn-eruptive processes is vital to deal with the increasing threat imposed to population and infrastructure by volcanoes that have been active historically and may potentially erupt in future. For many years, most of this knowledge was received from experiments on analogue materials and/or numerical models. In order to increase their significance and applicability for the “real” case, the natural complexity may not be oversimplified and the input parameters must be reliable and realistic. In the light of this, a close connection of field and laboratory work is essential. Volcanic eruptions may be phreatic, phreatomagmatic or magmatic, the latter scenario of which was addressed in this study. Rising magma is subject to decreasing lithostatic pressure. As a direct consequence, volatiles become increasingly oversaturated and bubbles will nucleate and grow depending on initial volatile content and melt viscosity. Both factors directly influence the diffusivity that limits the rate of bubble growth. Increasing amounts of bubbles increase the buoyancy difference to the surrounding rocks and lead to an acceleration of the rising melt-bubble mixture. Beside these limiting factors, the overpressure in the gas bubbles greatly depends on the magma’s ascent speed as it controls the residence time to conditions favourable to degassing (a combination of lithostatic pressure and magma temperature) and the time of overpressure reduction due to degassing. Volcanic eruptions occur when the bubbly melt can no longer withstand the exerted stress that derives from the overlying weight (lithostatic pressure), the expanding gas bubbles (internal gas overpressure) and different ascent velocities in the conduit (velocity profile). The melt will be fragmented and the gas-pyroclast mixture will be erupted. This study has combined close investigation of the deposits of the 1990-1995 eruption of Unzen volcano, Japan and detailed laboratory investigations on samples of this eruption and other volcanoes. The field work intended to reveal the density distribution of samples from within the eruptive products. Although all samples already underwent one eruption, their physical state (e.g. crystallinity, porosity) mostly remained close to sub-surface pre-eruption conditions due to their high viscosity and accordingly allowed their usage for the analysis of the fragmentation behaviour. In that purpose, rapid decompression experiments that simulate volcanic eruptions triggered by internal gas overpressure have been performed at 850 °C to evaluate fragmentation threshold and fragmentation efficiency. Laboratory investigations of that kind are one approach to bridge the gap between observational field volcanology and risk assessment as they reveal information on what can not be investigated closely but what is essential to know for realistic eruption models and the adjacent hazard mitigation. Changing the experimental conditions and close investigation of the artificial products reveals the influence of physical properties on the fragmentation behaviour. The density distribution inside a dome and the upper part of the conduit is crucial to the eruptive style of an explosive volcano. This information cannot be collected during an ongoing eruption but is important for future hazard assessment via modelling conduit flow and dome collapse/explosion behaviour. Therefore, the percentage of the mass fractions of all rock types in the primary and secondary volcanic deposits must be evaluated. For this purpose and at the lowest logistic effort, field-based density measurements have been performed on Unzen volcano, Japan. The resultant density distribution was found to be generally bimodal at constant peak values but changing peak ratios. The most abundant rock types at Unzen exhibited an open porosity of 8 and 20 vol.%, respectively. The porosity was found to be arranged in layers of cm- to dm-scale that were oriented subparallel to flow direction, i.e. subvertical within the conduit and flank-parallel within the dome lobes. The achieved results allowed for an internal picture of the dome during the last eruption of Unzen volcano. The evaluated picture of the density distribution within the uppermost parts of the conduit and the dome itself allowed for insights into and a better understanding of magma ascent and degassing conditions at Unzen volcano during its last eruption. Knowledge of the density distribution is additionally required to draw conclusions from the results of laboratory investigations on the fragmentation behaviour to the monitored behaviour of Unzen volcano during its last eruption. In the laboratory, the fragmentation behaviour upon rapid decompression has been investigated in a modified fragmentation bomb (Spieler et al., 2004). At 850 °C, initial overpressure conditions as high as 50 MPa have been applied to sample cylinders (25 mm diameter, 60 mm length) drilled from natural samples. In a first step, the minimum overpressure required to cause complete sample fragmentation (= fragmentation threshold, ΔPfr) has been evaluated. Results from samples of several volcanoes (Unzen, Montserrat, Stromboli, and Mt. St. Helens) showed that ΔPfr mainly depended on open porosity and permeability of the specific sample as these parameters were controlling pressure build-up and loss. The experiments further revealed that sample fragmentation was not the result of a single process but the result of a combination of simultaneously occurring processes as indicated by Alidibirov et al. (2000). The degree of influence of a single process to the fragmentation behaviour was found to be porosity-dependent. Further experiments at initial pressure conditions above ΔPfr and close investigation of the artificially generated pyroclasts allowed evaluating the fragmentation efficiency upon changing physical properties of the used samples. The efficiency of sample size reduction was investigated by grain-size analysis (dry sieving for particles bigger than 0.25 mm and wet laser refraction for particles smaller than 0.25 mm) and surface area measurements (by Argon adsorption). Results of experiments with samples of different porosities at different initial pressure values showed that the efficiency of fragmentation increased with increasing energy. The energy available for fragmentation was estimated from the open porosity and the applied pressure. A series of abrasion experiments was performed to shed light on the grain size reduction due to particle-particle interaction during mass movements. The degree of abrasion was found to be primarily depending on porosity and experimental duration. The results showed that abrasion may change the density distribution of block-and-ash flows (BAF) by preferentially abrading porous clasts. However, during the short drying interval prior to the analysis of the experimental pyroclasts, abrasion-induced grain-size reduction only played a minor role and was assumed to be negligible. Sat, 03 Dec 2005 23:00:00 GMT http://hdl.handle.net/2122/1169 2005-12-03T23:00:00Z http://hdl.handle.net/2122/1024 Title: On the origin of earthquake complexity in continuum fault models with rate and state friction Authors: Hillers, G.; PhD thesis Abstract: It is of great interest to isolate the fundamental physical mechanism controlling observed statistical properties of seismicity patterns. We present four numerical studies investigating the e ciency of uid related mechanisms and the role of fault zone heterogeneity in producing observed earthquake complexities. The 3-D models of the continuous class are governed by rate- and state-dependent friction and, depending on the problem, by elasto-hydraulic interactions or heterogeneous frictional properties on the 2-D fault plane. First, for certain ranges of hydraulically relevant parameters dilatant processes are shown to stabilize accelerating slip instabilities on a uid in ltrated fault, leading to nonuniform spatio-temporal slip evolution. The second model demonstrates the ability of heterogeneous pore pressure conditions in an undrained environment to produce complex slip pattern, where unstable sliding corresponds to regions with low degrees of overpressurization. In the third study we focus on the role of complex fault zone structure, parameterized by heterogeneous distributions of the rate and state slip weakening distance. The approach is shown to be a powerful and consistent method to generate seismicity patterns with properties similar to those of natural seismicity. Due to the e ciency of this parameterization we use it in the fourth study to investigate fault zones at di erent evolutionary stages and associated seismic response types. Using heterogeneous, correlated maps of the slip weakening distance we explore systematically the e ect of the range of size scales, correlation lengths and a statistical parameter related to roughness, on seismic response characteristics. In summary, we observe an increase in e ciency from the rst to the last study to generate synthetic seismicity with realistic statistical properties, suggesting that the range of size scales is the most fundamental parameter in explaining complex earthquake related phenomena. In the last part we analyze the generated synthetic seismicity catalogs with respect to their overall source scaling behavior. We nd that the general scaling trends of source properties of the simulated slip maps are in very good agreement with observations reported in the literature. We also show that the catalog of source models provides a useful resource on physically self-consistent scenario earthquakes for groundmotion simulations. We make use of this resource calculating waveforms and shake intensity maps for a suite of example events. Wed, 30 Nov 2005 23:00:00 GMT http://hdl.handle.net/2122/1024 2005-11-30T23:00:00Z