1,721,059 research outputs found
High-resolution seismic imaging in complex environments: A comparison among common-reflection-surface stack, common-midpoint stack, and prestack depth migration at the Ilva-Bagnoli brownfield site, Campi Flegrei, Italy
No full textI used the common-reflection-surface (CRS) stack technique together with conventional common-midpoint processing and prestack depth migration (PSDM) to process three parallel high-resolution seismic reflection lines acquired in a closed industrial plant. This brownfield site, now undergoing remediation, is located within the Bagnoli district of the city of Naples, Italy, near the southeastern border of Campi Flegrei caldera. Compared with the other results, the CRS stack, followed by poststack depth migration, produced a seismic image more consistent with the expected subsurface structures and with outcropping units present in the area. The survey confirmed the presence under the brownfield site of some buried steps of Coroglio Fault, a main structure formed approximately 15 ky ago, during the Neapolitan Yellow Tuff supereruption. Results have important implications for hazard assessment and geothermal exploration because the imaged faults certainly are preferential passageways for geothermal fluids and washed pollutants. These tests revealed that the common-reflection-surface stack can be a fast and cost-effective alternative to PSDM in settings in which structural complexity and high levels of ambient noise make it challenging to obtain a reliable background velocity model; therefore, allowing high-resolution reflection seismology to be successfully used in those environments. 2015 Society of Exploration Geophysicists
Structure and evolution of the Bay of Pozzuoli (Italy) using marine seismic reflection data: Implications for collapse of the Campi Flegrei caldera
No full textDigital marine seismic reflection data acquired in 1973 in the Bay of Pozzuoli, and recently reprocessed, were used to study the volcanological evolution of the marine sector of Campi Flegrei Caldera during the last 37 ka. In order to gain more information, interpretation also involved estimation of the "pseudo-velocity" and the "pseudo-density" from the resistivity logs of two onshore deep exploration wells. The main results are: (1) discovery of ancient pre-18 ka and post-37 ka submarine and mainly effusive volcanic activity, along coeval emission centers located at the edges of Campi Flegrei Caldera; (2) confirmation that the caldera collapse in the marine sector of Campi Flegrei seems strongly controlled by regional NE-SW and NW-SE structural discontinuities; (3) the finding of at least two episodes of collapse in the bay; and (4) identification of a post-18 ka volcanic deflation phase that has caused about 150-200 m of subsidence in the central sector of the Bay of Pozzuoli in the last 18 ka. © Springer-Verlag 2003
Very high-resolution seismic imaging in complex environments - A comparison among CRS, CMP and PSDM
No full textThe common-reflection surface stack technique was used, together with conventional common-midpoint and pre-stack depth migration to process a high-resolution seismic reflection line acquired in the dismissed industrial plant of ILVA. This brownfield site, now undergoing remediation, is located within the Bagnoli district of the city of Naples, near the southeastern border of Campi Flegrei caldera. The commonreflection surface stack, followed by post-stack depth migration, produced a seismic image more suited for a subsurface interpretation. Results reveal that the Common-Reflection-Surface stack can be a fast and cost-effective alternative to pre-stack depth migration in settings where structural complexity and high levels of ambient noise make it challenging to obtain a reliable background velocity model; therefore allowing high-resolution reflection seismology to be successfully employed in those environments. © (2015) by the European Association of Geoscientists & Engineers (EAGE)
Complex Trace Attributes of High-resolution CRS stacked data to interpret the near-surface-the example of Solfatara Cr
No full textTwo active-source, high-resolution seismic profiles were acquired in the Solfatara tuff cone in May and November 2014, with dense, wide aperture arrays which allowed recording multi-fold reflection data spanning a large range of offsets; deep penetrating refracted waves, suitable for first-arrival travel time tomography, and surface waves. The reflection profiles provide the first high-resolution seismic images of Solfatara crater, depicting a ~400m deep asymmetrical structure filled by volcanoclastic sediments and rocks. Seismic reflection data were interpreted using trace complex attributes which clearly locate several narrow (less than 10 m thick) areas with distinctive anomalous low amplitudes in several areas within the crater. We interpreted them as fluidfilled (both gas and liquid phases) conduits created by the intersection of NE- A nd NW-trending sets of subvertical faults. The imaged degassing pathways terminate against strong-amplitude zones created by reduction of porosity that occurs at about 100 m from crater surface and generates a high impedance contrast between fluid and dry soils
Location of cavities buried in the Neapolitan Yellow Tuff using the seismic reflection method
No full textA shallow seismic reflection survey was carried out at two sites near the city of Naples, where a large number of cavities have been dug over the past centuries into the Yellow Tuff Formation. To predict the response of the ground-cavity system to the seismic pulse, 2D synthetic wave propagation seismograms were produced using forward modelling theory. Then the seismic data were processed in two different ways to search for the diffraction hyperbolae generated by the cavity, and for any breaks in seismic reflectors below the area where the cavity is located. At the first site (Frattaminore), we were able to detect the diffraction hyperbolae, and with them to calculate the depth of the cavity. Here, we could also record the reflection from the top of the volcanic tuff; but, because of the complex environment and of the data quality, deeper reflections were not well visible on the seismogram. Thus, in order to improve the temporal resolution of the records and their signal-tonoise ratio, the data were processed by deconvolution and F-K dip-filtering. After this other, deeper events appeared on the section, but not in the depth range of the cavity. Despite the similar geological conditions of the two sites, it was not possible to record good seismic data at Grumo Nevano, due to the different environmental noise. © 1997 Osservatorio Geofisico Sperimentale
Comment on "A new model for the formation of the Somma Caldera" (2004) by G. Rolandi, F. Bellucci, and M. Cortini
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Near-surface voids in the Neapolitan Volcanic Tuff (Italy) detected by seismic refraction tomography
No full textThe Neapolitan area (Italy) is affected by the presence of shallow man-made cavities in volcanic tuffs that were used in the past as building material. Therefore, the identification of these voids is a fundamental prerequisite for the minimization of subsurface collapse risks. In the past few years, several authors have shown that the geophysics prospecting methods can provide a most convenient solution to detecting underground voids. In this work we show how the seismic refraction tomography represents a powerful tool for the detection of near-surface tuff-cavities located in Casamarciano, Naples. The interpolation of the velocity models, allowed us to build a three-dimensional model of the tuff basement top and to show the lateral extend of the voids. The cavity location detected by seismic refraction tomography has been subsequently confirmed by four core-drilling made in the area. © (2015) by the European Association of Geoscientists & Engineers (EAGE)
The role of flank failure in modifying the shallow plumbing system of volcanoes: An example from Somma-Vesuvius, Italy
No full textThe joined interpretation of structural, geophysical, historical and DTM-extracted data collected on the Somma-Vesuvius volcano reveals the presence of a spoon-shaped paleo-depression, which is masked by the well known Vesuvius subsidence caldera. Such depression was caused by failure of the Somma southwestern flank. The flank failure was triggered by dike intrusion along a pre-existing structural discontinuity. This event occurred between 20-25 and 18ka and marked a change in the composition of erupted products and style of activity, which shifted from an effusive and strombolian activity to a plinian-type activity. The flank failure induced a reorientation of the gravity-induced stress trajectory, which, below the depression, resulted parallel to the surface. This prevented the ascent of magma to the surface allowing the formation of a shallow reservoir in which more felsic magma evolved. When the magma pressure exceeded a critical value, plinian activity began. The joined interpretation of structural, geophysical, historical and DTM-extracted data collected on the Somma-Vesuvius volcano reveals the presence of a spoon-shaped paleodepression, which is masked by the well known Vesuvius subsidence caldera. Such depression was caused by failure of the Somma southwestern flank. The flank failure was triggered by dike intrusion along a pre-existing structural discontinuity. This event occurred between 20-25 and 18 ka and marked a change in the composition of erupted products and style of activity, which shifted from an effusive and strombolian activity to a plinian-type activity. The flank failure induced a reorientation of the gravity-induced stress trajectory, which, below the depression, resulted parallel to the surface. This prevented the ascent of magma to the surface allowing the formation of a shallow reservoir in which more felsic magma evolved. When the magma pressure exceeded a critical value, plinian activity began
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