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Gautier, S.
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Gautier, S.
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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 - PublicationRestrictedA New Passive Tomography of the Aigion Area (Gulf of Corinth, Greece) from the 2002 Data SetWe present the results of a tomographic study performed in the framework of the 3F-Corinth project. The aim of this work is to better understand the rifting process by imaging the crustal structure of the western Gulf of Corinth. Forty-nine stations were deployed for a period of six months, allowing us to monitor the microseismicity. Delayed P and S first-arrival times have been simultaneously inverted for both hypocenter locations and 3-D velocity distributions. We use an improved linearized tomography method based on an accurate finite-difference travel-time computation to invert the data set. The obtained Vp and Vs models confirm the presence of a two-layer vertical structure characterized by a sharp velocity gradient lying at 5–7 km depth, which may be interpreted as a lithological contrast. The shallower part of the crust (down to 5 km depth) is controlled by the N-S extension and lacks seismicity. The deeper part (7–13 km depth) matches the seismogenic zone and is characterized by faster and more heterogeneous anomalies. In this zone, the background seismicity reveals a low-angle active surface dipping about 20° toward the north and striking WNW-ESE. The position of this active structure is consistent with both high Vp/Vs and low Vp.Vs anomalies identified at 8–12 km depth and suggesting a highly fracturated and fluid-saturated zone. Both the geometry of the active structure beneath the gulf and the presence of fluids at 8–12 km depth are in accordance with a low-angle detachment model for the western part of the Gulf of Corinth.
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