1,721,053 research outputs found
Analisi litostratigrafica e geofisica comparata delle prove down-hole eseguite nell’ambito del progetto “Microzonazione sismica della conca aquilana”
No full textStructural setting of the Bay of Naples (Italy) seismic reflection data: Implications for Campanian volcanism
No full textThis paper focuses on the recent tectonic evolution of the Bay of Naples with the aim of exploring the connection between local tectonics and volcanism. We reprocessed the seismic reflection dataset acquired in the area in the late 1973. The new processing was highly successful in obtaining a decisive strong reduction of random noise, removal of coherent noise and reduction of spatial aliasing. Classical interpretative schemes and complex attributes of seismic traces were used to reconstruct fault kinematics and reflector patterns. The results show that the faults affecting the Bay of Naples exhibit prevailing NE structural strikes, with the exception of the Pozzuoli Caldera where NW patterns are also common. Many faults are subvertical and show seismic evidence of volcanic activity along them. A main alignment of conjugate NE-SW faults, named here as "Magnaghi-Sebeto line", intersects several submarine volcanic banks and separates the bay into two sectors, characterized by important geological, geophysical and petrochemical differences. The structural configuration of the bay may reflect the occurrence of either oblique extension or a transfer zone of the NW-SE fault system, along which, in the Campanian-Lucanian Apennine chain, great vertical displacements occur. © 2003 Elsevier B.V. All rights reserved
Earth modelling and estimation of the local seismic ground motion due to site geology in complex volcanoclastic areas
No full textSTRUCTURAL SETTING OF THE BAY OF NAPLES (ITALY) FROM SEISMIC REFLECTION DATA: IMPLICATIONS FOR THE CAMPANIA VOLCANISM
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CHARACTERIZATION OF SHALLOW VOLCANOCLASTIC DEPOSITS BY TURNING RAY SEISMIC TOMOGRAPHY: AN APPLICATION TO URBAN ENVIROMENTS IN NAPLES AREA (S. ITALY)
No full textSeveral bidimensional seismic tomography surveys were carried out in urban areas of the Campi Flegrei and Somma-Vesuvius volcanic districts, Naples, Italy, with the aim of investigating the shallow subsurface and of detecting small-scale variation and heterogeneities within pyroclastic deposits. The method employed in this study is turning ray tomography (TRT). With accurate field acquisition and travel time picking and correct choice of inversion parameters, it was possible to obtain detailed P-wave tomographic models in areas characterized by thick beds of pyroclastic deposits. We were able to identify zones with heterogeneous P-wave velocities caused by the presence of buried paleochannels, or by differential welding and zeolitization in the subsurface of the investigated areas. TRT appears to be a suitable method to investigate deposits for engineering applications, at sites where the bedrock is too deep to be reached by foundations and the overburden is characterized by much heterogeneity. © 2002 Elsevier Science B.V. All rights reserved
Seismic study of the '41st Parallel' fault system offshore the Campanian-Latial continental margin, Italy
No full textA set of seismic reflection lines, collected in the Southern Tyrrhenian Sea offshore the Campanian-Latial continental margin has been selected and interpreted. The aim is to characterize: (1) the structural features of the 41st Parallel Line (41PL), an E-W elongated magnetic anomaly zone separating the Northern Tyrrhenian domain from the Southern Tyrrhenian domain; and (2) to study the relationships between the 41PL and the Ortona-Roccamonfina Line (ORL), a tectonic structure transversal to the Apennines along which the Northern Apennine Arc merges the Southern Arc. The interpretation of the seismic lines is discussed in light of the available geological (stratigraphic and structural) and geophysical (gravimetric and magnetic) information. Results show that the Campanian-Latial continental margin is characterized by a series of structural lows and highs that match with the main structures on the mainland (Mt. Massico horst, the Volturno and Garigliano depressions). The study area is characterized by ESEWNW to E-W and NE-SW striking faults. The activity of these faults developed during Pliocene-Early Pleistocene times. ESE-WNW to E-W faults display structures consistent with strike-slip movements. These faults, which are located on the maximum gradient of the E-W elongated magnetic alignment of 41PL, are responsible for the SSE translation of the offshore sector of the Mt. Massico horst. The horizontal dislocation of Mt. Massico suggests left-lateral movements for the ESE-WNW to E-W faults. The NE-SW faults that affect the Mt. Massico horst, which represents the southern tip of ORL, show seismic features consistent with normal movements, as also revealed by inland data. Since: (1) background seismicity is virtually absent along the study area; and (2) the uppermost seismic reflectors seem unaffected by faults, it is very likely that both the ORL and 41PL fault zones are now inactive, at least in the Campanian-Latial area. Seismic data indicate that ORL is older than 41PL and support the interpretation that the 41PL represents a deep-seated transfer fault system formed in response to the different rates of opening of the Tyrrhenian Sea. The strike-slip movements along the 41PL faults and the normal movements along the ORL faults are consistent with a NW-SE extension, which is responsible for the longitudinal extension in the Southern Apennines belt. (C) 2000 Elsevier Science B.V. All rights reserved
Geophysical and hydrogeological experiments from a shallow hydrothermal system at Solfatara Volcano, Campi Flegrei, Italy: Response to caldera unrest
No full textIntegration of high-resolution geophysical and hydrogeological investigations at Solfatara Volcano, Campi Flegrei, Italy, allowed us to (1) image the shallow and intermediate subsurface to the crater, (2) elucidate patterns in the shallow subsurface degassing, and (3) refine and upgrade volcano-monitoring strategies for this dynamic area. Our results show that the subsurface to the crater can be divided roughly into two zones: a dry, outcropping layer overlying a horizon saturated by hydrothermal fluids. Within this saturated zone, intersections of dominant NW-and ENE-striking structural lineaments act as preferential escape conduits for the fluids which generate high microseismic noise amplitudes in the southeastern part of the crater. Hydrogeological data suggest an uprising of the isotherms below Solfatara crater, and a marked increment of fluid degassing, over the last 40 years. Sudden variations of both seismic noise level and noise cycling are positively correlated with early stages of ground inflation during the AD 2000 uplift. We believe therefore that monitoring of seismic noise can be used for upgrading early warning strategies in this sector of the Campi Flegrei volcanic system. Copyright 2007 by the American Geophysical Union
Influence of geometrical and geophysical parameters on the seismic site amplification factor
No full textAn evaluation of the intrinsic of 1D modelling for estimation of the site seismic response (DAF, Dynamic Amplification Factor) in the case a non-horizontal basement is presented and discussed. 1D models are still commonly used in engineering practice. Therefore it is important to understand the limits of the 1D modelling in order to simplify the problem without dangerous errors when evaluating the seismic response. Up-to-date and robust visco-elastic non-linear 1D and 2D algorithms were used. The reference accelerogram is relative to an Umbria earthquake (Colfiorito - Italy, 26/09/97, M=5.6), recorded at the Department of Geophysics and Volcanology, University of Naples Federico II. The results indicate that in the case of a dipping bedrock, if the angle is less than 10°and the S-wave velocity contrast within the overburden is included between 1 - 0.5, the evaluation of the site response given by both the algorithms is similar. For dip values exceeding 10°, the DAF spectra start to diverge, both in terms of amplitude and peak periods. If the S-wave velocity contrast is less than 0.5 the 1D and 2D DAF spectra are substantially different even if the bedrock is horizontal and this is due to the different method of DAF calculation used by the two algorithms. The results obtained with theoretical models were confirmed by comparing the 1D and the 2D response in two test sites characterised by a dipping volcanic tuff basement, in the city of Naples. The response of the 1D models in such geological conditions is inaccurate. Therefore the use of 1D algorithms for DAF evaluation during seismic site planning should be restricted to those sites having geophysical and geometrical properties compatible with those illustrated in the results
A critical review of potential tsunamigenic sources as first step towards the tsunami hazard assessment for the Napoli Gulf (Southern Italy) highly populated area
No full textCatastrophic tsunami events like those occurred in Papua New Guinea in 1998, Sumatra in 2004 and Japan in 2011, attracted the attention of the scientific community and promoted the development of different tools for assessing tsunami hazard. A preliminary step towards this goal is the knowledge of the events which might affect a specific coastal zone. In this context, we propose a method to identify the tsunami events possibly occurring in areas characterized by scarce data and a non-conservative environment. Accordingly, we propose different indices to summarize the knowledge on tsunami triggering mechanisms (earthquakes, landslides, volcanic eruptions), the characteristics of those mechanisms (magnitude of earthquakes, volume of landslide, Volcanic Explosivity Index) and tsunami features (water height, run-up, wave amplitude, propagation time). This knowledge, considered over a wider area than that of interest, allows for a paramount vision of possible hazardous events that could affect a particular coastal zone. Moreover, the tsunami simulation data and the analysis of potentially tsunamigenic slides which occurred on the Campania continental margins were also considered in the analysis. We focused our attention on Napoli megacity, because the high population density (about 1 million of people live on a territory of 117 km2), together with the presence of active volcanic areas (Ischia, Somma-Vesuvio and Campi Flegrei), make this city potentially exposed to tsunami risk. The main outcome of such an approach shows that in the near field a tsunami amplitude varying from a few centimetres (30–40 cm) to some metres (1–4 m) might be expected at the coastline if the tsunami event was triggered by volcanic activity, whereas no relevant tsunami event should be expected given the peculiar seismicity of the Neapolitan volcanic areas, with earthquakes rarely exceeding 4 Mw, if any possible cascade effects are overlooked. A morphometric analysis of high-resolution bathymetry collected between Ventotene Island and the Gulf of Salerno has shown that the submarine southern sectors of the Ischia Island and the Sorrento Peninsula are characterized by a high density of landslide scars, being thus a potential source area of landslide-generated tsunamis. However, despite the susceptibility of these areas to recurrent slope failures, only four submarine landslide scars were found to be potentially tsunamigenic with estimated tsunami amplitude of few metres at the coastline as predicted by coupling slide morphometry with tsunami amplitude equations. Concerning the tsunamis generated by earthquakes in the Western Mediterranean, only those triggered by high magnitude events (value ≥ 6–7 Mw) might affect the city of Napoli with an amplitude not exceeding 0.5 m, in about 30
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