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Piegari, Ester
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- PublicationRestrictedThe 847 CE earthquake in central-southern Italy: New hints from archaeosismological and geophysical investigations in the Volturno River Valley area(2020-01-05)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Integration of archaeoseismic observations, geological and geophysical surveys and a critical review of historical written sources contributed to shed light on the effects of the 847 earthquake AD that struck a large area of Southern-Central Italy. New archaeoseismic evidence of a strong earthquake comes from two Medieval archaeological sites along the Volturno Valley, between Campania and Molise regions, which occurred around the middle of the ninth century AD. Evidence includes the tilting of pillars in the Basilica of Santa Maria near Alvignano (northern Campania) and a collapsed masonry wall in the Abbey of San Vincenzo al Volturno near Isernia (northern Molise). At Alvignano, a site so far unrecorded in seismic catalogues for the 847 earthquake, geoelectrical and georadar investigations were used to explore the subsoil and study local site conditions, which could have influenced coseismic ground motion. Integrated interpretation of geophysical surveys and borehole logs document the presence of altered pyroclastic deposits, which certainly enhanced site effects at Alvignano. Analysis of damage descriptions and of archaeological reports indicate that the 847 seismic event documented by historical sources damaged a wide area between Latium, Campania and Molise, with destruction of the town of Isernia. Although historical sources did not explicitly mention damage in Rome, seismic effects attributed to the 847 event are recorded in the archaeological and seismological literature. Because the damaged area for this medieval earthquake is loosely defined due to the scanty documentation, the present study represents an important contribution to better define the shaking area and provide new hints on the extent and location of the possible seismogenic source.347 2 - PublicationOpen AccessElectric effects induced by artificial seismic sources at Somma-Vesuvius volcano(2013)
; ; ; ; ;Di Maio, R. ;Cecere, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;De Martino, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Piegari, E.; Università di Napoli “Federico II”, Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, ;; ; In this paper, we present a series of self-potential measurements at Somma-Vesuvius volcanic area acquired in conjunction with an active seismic tomography survey. The aim of our study is both to provide further confirmation to the occurrence of seismo-electric coupling and to identify sites suitable for self-potential signal monitoring at Somma-Vesuvius district. The data, which were collected along two perpendicular dipoles, show significant changes on the natural electric field pattern. These variations, attributable to electrokinetic processes triggered by the artificial seismic waves, were observed after explosions occurred at a distance less than 5 km from the SP dipole arrays. In particular, we found that the NW-SE component of the natural electric field was more sensible to the shots than the NE-SW one, and the major effects did not correspond to the nearest shots. Such evidences were interpreted considering the underground electrical properties as deduced by previous detailed resistivity and self-potential surveys performed in the study area.348 148 - PublicationOpen AccessLate miocene-early pliocene out-of-sequence thrusting in the Southern Apennines (Italy)(2020-08-06)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; We present a structural study on late Miocene-early Pliocene out-of-sequence thrusts affecting the southern Apennine orogenic belt. The analyzed structures are exposed in the Campania region (southern Italy). Here, thrusts bound the N-NE side of the carbonate ridges that form the regional mountain backbone. In several outcrops, the Mesozoic carbonates are superposed onto the unconformable wedge-top basin deposits of the upper Miocene Castelvetere Group, providing constraints to the age of the activity of this thrusting event. Moreover, a 4-km-long N-S oriented electrical resistivity tomography profile, carried out along the Caserta mountains, sheds light on the structure of this thrust system in an area where it is not exposed. Further information was carried out from a tunnel excavation that allowed us to study some secondary fault splays. The kinematic analysis of out-of-sequence major and minor structures hosted both in the hanging wall (Apennine Platform carbonates) and footwall (Castelvetere Group deposits and Lagonegro-Molise Basin units) indicates the occurrence of two superposed shortening directions, about E-W and N-S, respectively. We associated these compressive structures to an out-of-sequence thrusting event defined by frontal thrusts verging to the east and lateral ramp thrusts verging to the north and south. We related the out-of-sequence thrusting episode to the positive inversion of inherited normal faults located in the Paleozoic basement. These envelopments thrust upward to crosscut the allochthonous wedge, including, in the western zone of the chain, the upper Miocene wedge-top basin deposits.60 42 - PublicationRestrictedFiltering of noisy magnetotelluric signals by SOM neural networksThis work presents a systematic study for testing the effectiveness of Self-Organizing Map (SOM) neural networks in filtering magnetotelluric (MT) data affected by cultural noise. Although the MT method is widely used for geophysical investigation of the Earth’s interior, it is very sensitive to anthropogenic noise sources (e.g., power lines, electric railways, etc.), which can generate transient artificial electromagnetic fields disturbing the MT records. Thus, when not properly detected, man-made noises could lead to a distortion of the MT impedance tensors and consequently to wrong estimate of the resulting subsoil resistivity distribution. The choice to use SOM networks to filter noisy MT data comes from the expectation that the impedance tensors, estimated by Discrete Wavelet Transform analysis of MT time series, will cluster differently in presence of noise. This expectation is confirmed by the results of our extensive study on synthetic MT signals affected by temporally localized noise, which show that noisy and noise-free impedance tensor values distribute in well separate clusters. Moreover, as the SOM analysis provides a grid of weights (clusters), each one close to a particular subset of the input data, a criterion is proposed for selecting the cluster that gives the most reliable impedance tensor estimate. An application of the proposed SOM-based filtering procedure to actual MT data demonstrates its efficiency in denoising real MT signals.
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