http://hdl.handle.net/2122/290 Search the Channel search http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/2974 Title: Magma chamber evolution prior to the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions (Campi Flegrei, Italy) <br/> <br/>Authors: Pabst, S.; Abteilung Geochemie, GZG, Georg-August-Universität Göttingen, Goldschmidtstr. 1, 37077 Göttingen, Germany; Wörner, G.; Abteilung Geochemie, GZG, Georg-August-Universität Göttingen, Goldschmidtstr. 1, 37077 Göttingen, Germany; Civetta, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Tesoro, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia <br/> <br/>Abstract: Abstract The Campi Flegrei (Campanian Region, Italy) experienced two cataclysmic caldera-forming eruptions which produced the Campanian Ignimbrite (39 ka, CI) and the Neapolitan Yellow Tuff (15 ka, NYT). We studied the minor eruptions before both these large events to understand magma chamber evolution leading towards such catastrophic eruptions. Major, trace element, and Sr and Nd isotope compositions of pre-Campanian Ignimbrite and pre- Neapolitan Yellow Tuff products define distinct geochem- ical groups, which are here interpreted as distinct magma batches. These batches do not show any transitional trend towards the CI and NYT eruptions. The CI and NYT systems are decoupled geochemically and isotopically. At least one of the pre-CI and one of the pre-NYT erupted magma batches qualifies as mixing endmembers for the large CI and NYT eruptions, and thus, must have been stored in reservoirs for some time to remain available for the CI and NYT eruptions. The least evolved, isotopically distinct magma compositions that are typical of the last phases of the NYT and CI eruptions did not occur before caldera-forming events. Based on the new data, we propose the following scenario: Multiple magma chambers with distinct compositions existed below the Campi Flegrei before the CI and NYT eruptions and remained generally separated for some time unless new magma was recharged. In each case, one of the residing magma reservoirs was recharged by a new large-volume magma input of interme- diate composition from a deeper differentiating magma reservoir. This may have triggered the coalescence of the previously separated reservoirs into one large chamber which fed the cataclysmic caldera-forming eruption. Large magma chambers in the Campi Flegrei may therefore be ephemeral features, interrupted by periods of evolution in individual, separated magma reservoirs. Sun, 29 Oct 2006 22:58:59 GMT http://hdl.handle.net/2122/1879 Title: Automatic processing of seismic events recorded on a mini-array Signal analysis combined with neural networks <br/> <br/>Authors: Bottero, A.; Laboratoire de Détection et de Géophysique, Bruyeezs-Le-Chatel, France; Cansi, Y.; Laboratoire de Détection et de Géophysique, Bruyeezs-Le-Chatel, France; Massinon, B.; Laboratoire de Détection et de Géophysique, Bruyeezs-Le-Chatel, France <br/> <br/>Abstract: We present a new method for automatic processing of mini-array records of regional events. It is based on a comprehensive analysis of the cross-correlation functions. This leads to a set of time-delays used to compute the azimuth and velocity of the travelling wave only in case of consisteney of the time-delay set. The second step takes into account the time-frequency representations of these wave parameters to identify each regional wave using a neural network. The resulting standard error on azimuth is 3° and the relative error on distance is less than 20%. Mon, 29 Aug 1994 22:58:59 GMT http://hdl.handle.net/2122/1833 Title: Focusing inversion techniques applied to electrical resistance tomography in an experimental tank <br/> <br/>Authors: Pagliara, G.; Math4Tech, Mathematics Department, University of Ferrara, Italy; Vignoli, G.; L.A.R.A. Group, Earth Sciences Department, University of Ferrara, Italy <br/> <br/>Abstract: We present an algorithm for focusing inversion of electrical resistivity tomography (ERT) data. ERT is a typical example of ill-posed problem. Regularization is the most common way to face this kind of problems; it basically consists in using a priori information about targets to reduce the ambiguity and the instability of the solution. By using the minimum gradient support (MGS) stabilizing functional, we introduce the following geometrical prior information in the reconstruction process: anomalies have sharp boundaries. The presented work is embedded in a project (L.A.R.A.) which aims at the estimation of hydrogeological properties from geophysical investigations. L.A.R.A. facilities include a simulation tank (4 m x 8 m x 1.35 m); 160 electrodes are located all around the tank and used for 3-D ERT. Because of the large number of electrodes and their dimensions, it is important to model their effect in order to correctly evaluate the electrical system response. The forward modelling in the presented algorithm is based on the so-called complete electrode model that takes into account the presence of the electrodes and their contact impedances. In this paper, we compare the results obtained with different regularizing functionals applied on a synthetic model. Sat, 02 Sep 2006 22:58:59 GMT http://hdl.handle.net/2122/1832 Title: Focusing inversion technique applied to radar tomographic data <br/> <br/>Authors: Vignoli, G.; Università di Ferrara, Dipartimento di Scienze della Terra, Via Saragat 1, 4100 Ferrara, Italy; Zanzi, L.; Politecnico di Milano, Dipartimento di Ingegneria Strutturale, Piazza Leonardo da Vinci 32, 20133 Milano, Italy <br/> <br/>Abstract: Traveltime tomography is a very effective tool to reconstruct acoustic, seismic or electromagnetic wave speed distribution. To infer the velocity image of the medium from the measurements of first arrivals is a typical example of ill-posed problem. In the framework of Tikhonov regularization theory, in order to replace an ill-posed problem by a well-posed one and to get a unique and stable solution, a stabilizing functional (stabilizer) has to be introduced. The stabilizer selects the desired solution from a class of solutions with a specific physical and/or geometrical property; e.g., the existence of sharp boundaries separating media with different petrophysical parameters. Usually stabilizers based on maximum smoothness criteria are used during the inversion process; in these cases the solutions provide smooth images which, in many situations, do not describe the examined objects properly. Recently a new algorithm of direct minimization of the Tikhonov parametric functional with minimum support stabilizer has been introduced; it produces clear and focused images of targets with sharp boundaries. In this research we apply this new technique to real radar tomographic data and we compare the obtained result with the solution generated by the more traditional minimum norm stabilizer. Sat, 03 Sep 2005 22:58:59 GMT