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Stanford Rock Physics Laboratory, Stanford University, Stanford, CA, USA
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- PublicationRestrictedThe Campi Flegrei Blind Test: Evaluating the Imaging Capability of Local Earthquake Tomography in a Volcanic Area(2012)
; ; ; ; ; ; ; ; ; ; ; ; ;Priolo, E.; Dipartimento Centro di Ricerche Sismologiche (CRS), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS) ;Lovisa, L.; Dipartimento Centro di Ricerche Sismologiche (CRS), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS) ;Zollo, A.; Dipartimento di Scienze Fisiche, Universit`a degli Studi di Napoli “Federico II”,Napoli, Italy ;B¨ohm, G.; Dipartimento di Geofisica della Litosfera (GDL), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS), Trieste, Italy ;D’Auria, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Gautier, S.; G´eosciences Montpellier, UMR 5243 CNRS, University Montpellier 2, Montpellier, France ;Gentile, F.; Dipartimento Centro di Ricerche Sismologiche (CRS), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS) ;Klin, P.; Dipartimento Centro di Ricerche Sismologiche (CRS), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS) ;Latorre, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Michelini, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Vanorio, T.; Stanford Rock Physics Laboratory, Stanford University, Stanford, CA, USA ;Virieux, J.; Institut des Sciences de la Terre (ISTerre), The Universit´e Joseph Fourier, Grenoble, France; ; ; ; ; ; ; ; ; ; ; During the 1982–1984 bradyseismic crises in the Campi Flegrei area (Italy), the University of Wisconsin deployed a network of seismological stations to record local earthquakes. In order to analyse the potential of the recorded data in terms of tomographic imaging, a blind test was recently set up and carried out in the framework of a research project. A model representing a hypothetical 3D structure of the area containing the Campi Flegrei caldera was also set up, and a synthetic dataset of time arrivals was in turn computed. The synthetic dataset consists of several thousand P- and S-time arrivals, computed at about fourteen stations. The tomographic inversion was performed by four independent teams using different methods. The teams had no knowledge of either the input velocity model or the earthquake hypocenters used to create the synthetic dataset. The results obtained by the different groups were compared and analysed in light of the true model. This work provides a thorough analysis of the earthquake tomography potential of the dataset recording the seismic activity at Campi Flegrei in the 1982–1984 period. It shows that all the tested earthquake tomography methods provide reliable low-resolution images of the background velocity field of the Campi Flegrei area, but with some differences. However, none of them succeeds in detecting the hypothetical structure details (i.e. with a size smaller than about 1.5–2 km), such as a magmatic chamber 4 km deep and especially the smaller, isolated bodies, which represent possible magmatic chimneys and intrusions.359 30 - PublicationRestrictedSeismic images and rock properties of the very shallow structure of Campi Flegrei caldera (southern Italy)(2009-03)
; ; ; ; ; ;Dello Iacono, Dario; Dipartimento di Scienze Fisiche, Università di Napoli Federico II, Napoli, Italy ;Zollo, Aldo; Dipartimento di Scienze Fisiche, Università di Napoli Federico II, Napoli, Italy ;Vassallo, Maurizio; Dipartimento di Scienze Fisiche, Università di Napoli Federico II, Napoli, Italy ;Vanorio, Tiziana; Stanford Rock Physics Laboratory, Stanford University, Stanford, CA, USA ;Judenherc, Sebastien; Dipartimento di Scienze Fisiche, Università di Napoli Federico II, Napoli, Italy - Agecodagis, sarl, Rieux Volvestre, France; ; ; ; In September 2001, an extensive active-seismic investigation (Serapis experiment) was carried out in the Gulfs of Naples and Pozzuoli, with the aim of investigating and reconstructing the shallow crustal structure of the Campi Flegrei caldera, and possibly identifying its feeding system at depth. The present study provides a joint analysis of the very shallow seismic reflection data and tomographic images based on the Serapis dataset. This is achieved by reflection seismic sections obtained by the 3D data gathering and through refined P-velocity images of the shallowest layer of Pozzuoli Gulf (z<1,000 m). From the refined Vp model, the overall picture of the velocity distribution confirms the presence of a complex arc-shaped anomaly that borders the bay offshore. The deeper part of the anomaly (beneath 700 m, with Vp>3,500 m/s) correlates with units made up of agglomerate tuffs and interbedded lava, which form the southern edge of the caldera, which was probably formed following the two large ignimbritic eruptions that marked the evolutionary history of the area under study. The upper part of the anomaly that tends to split into two parallel arcs is correlated with dikes, volcanic mounds and hydrothermal alteration zones noted in previous shallow reflection seismic analyses. The depth of the transition between the upper and lower parts of the anomaly is characterized by an abrupt Vp increase on the one-dimensional (1D) profiles extracted from the 3D tomographic model and by the presence of a strong reflector located at about 0.6/0.7 s Two Way Time (TWT) on Common Mid Point gathers. The move-out velocity analysis and stack of the P–P and P–S reflections at the layer bottom allowed to estimate relatively high Vp/Vs values (3.7±0.9). This hypothesis has been tested by a theoretical rock physical modeling of the Vp/Vs ratio as a function of porosity suggesting that the shallow layer is likely formed by incoherent, water saturated, volcanic and marine sediments that filled Pozzuoli Bay during the post-caldera activity.143 27 - PublicationOpen AccessThree-dimensional tomography and rock properties of the Larderello-Travale(2008-11)
; ; ; ; ; ; ;De Matteis, R.; Dipartimento di Studi Geologici ed Ambientali, Università del Sannio ;Vanorio, T.; Department of Geophysics, Stanford University ;Zollo, A.; Dipartimento di Scienze Fisiche, Università di Napoli Federico II ;Ciuffi, S.; ENEL GEM-Geothermal Production ;Fiordelisi, A.; ENEL GEM-Geothermal Production ;Spinelli, E.; ENEL GEM-Geothermal Production; ; ; ; ; In a geothermal area, a detailed knowledge of the three-dimensional velocity structures aids the managementof the field and the further development of the geothermal source. Here,we present a high-resolution study of the three-dimensional S-wave velocity structures from microearthquake travel times for the Larderello-Travale geothermal field, Italy.We have also deduced the Vp/Vs and Vp ×Vs parameters for this area toemphasize the deep variations in the physical rock properties due to fluid content and porosity. Furthermore, effective porousmedium modelling has been performed for site-relevant lithologies, to improve our interpretation of the results in terms of rock physics signatures. This has allowed us to estimate the variation range of the seismological parameters investigated, as well as their sensitivity for suitable rock under specific physical conditions. LowVp/Vs anomalies, arising froma lower Vp compared to Vs, dominate the geothermal field of Larderello-Travale. These have been interpreted as due to steam-bearing formations. On the contrary, analysis of Vp ×Vs images provides information on the relative changes in rock porosity at depth. Comparison of tomographic section images with previously interpreted seismic lines suggests that the reflective ‘K-horizon’ delineates a transition between zones that have different porosities or crack gatherings. The ‘K-horizon’ also lies on low Vp/Vs anomalies, which suggests a steam saturation zone, despite the reduced porosity at this depth.247 298 - PublicationOpen AccessA 3D velocity model for earthquake location in Campi Flegrei area: application to the 1982-84 uplift event(2006)
; ; ; ; ; ; ; ; ;Satriano, C.; Dipartimento di Scienze Fisiche, Università Federico II, Napoli, Italy ;Zollo, A.; Dipartimento di Scienze Fisiche, Università Federico II, Napoli, Italy ;Capuano, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Russo, G.; Dipartimento di Scienze Fisiche, Università Federico II, Napoli, Italy ;Vanorio, T.; Géosciences Azur, CNRS, Université de Nice, Sophie Antinopolies, Valbonne, France ;Caielli, G.; Istituto per la Dinamica dei Processi Ambientali, CNR, Milano, Italy ;Lovisa, L.; Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Trieste, Italy ;Moretti, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; ; ; ; ; ; ; The uplift crisis of the 1982-1984 in the Campi Flegrei area underlined the importance of seismic surveillance for this volcanic caldera. One of the key elements for an effective seismic network is to make use of a reliable velocity model for earthquake location. In the present work we will discuss criteria for the construction and validation of a new 3D P-wave velocity model for earthquake location in the Campi Flegrei area built from the integration of two high-resolution 3D tomographic images of the region. The model is used for locating a group of earthquakes from the uplift event of the 1982-1984.244 327 - PublicationOpen AccessA rock physics and seismic tomography study to characterize the structure of the Campi Flegrei caldera(2006)
; ; ; ; ; ;Vanorio, T.; Géosciences Azur, CNRS, Université de Nice, Sophie Antinopolies, Valbonne, France ;Virieux, J.; Géosciences Azur, CNRS, Université de Nice, Sophie Antinopolies, Valbonne, France ;Zollo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Capuano, P.; Dipartimento di Scienze e Tecnologie per l’Ambiente e il Territorio, Università del Molise ;Russo, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; ; ; The Campi Flegrei (CF) caldera experiences dramatic ground deformations unsurpassed anywhere in the world. The source responsible for this phenomenon is still debated. With the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes, a multidisciplinary approach dealing with 3-D delay-time tomography and rock physics characterization has been followed. Selected seismic data were modeled by using a tomographic method based on an accurate finite-difference travel-time computation which simultaneously inverts P-wave and S-wave first-arrival times for both velocity model parameters and hypocenter locations. The retrieved P-wave and S-wave velocity images as well as the deduced Vp/Vs images were interpreted by using experimental measurements of rock physical properties on CF samples, to take into account steam/water phase transition mechanisms affecting P-wave and S-wave velocities. Also, modelling of petrophysical properties for site-relevant rocks constrains the role of overpressured fluids on velocity. A flat and low Vp/Vs anomaly lies at 4 km depth under the city of Pozzuoli. Earthquakes are located at the top of this anomaly. This anomaly implies the presence of fractured over-pressured gas-bearing formations and excludes the presence of melted rocks. At shallow depth, a high Vp/Vs anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase. Finally, maps of the Vp*Vs product show a high Vp*Vs horse-shoe shaped anomaly located at 2 km depth. It is consistent with gravity data and well data and might constitute the on-land remainder of the caldera rim, detected below sea level by tomography using active source seismic data. For a more exhaustive description of the utilized methodologies, of synthetic tests for spatial resolution and uncertainty assessment and, the interpretation of results, the reader may refer to the paper Vanorio et al. (2005).234 633