1,720,986 research outputs found
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)
High-resolution onshore seismic imaging of complex volcanic structures: An example from Vulcano Island, Italy
Full text linkDetailed seismic images of subsurface structures of volcanic calderas are fundamental to improve the structural and volcanological knowledge of these high-risk volcanoes. However, high-quality seismic data are difficult to obtain in volcanic areas, especially on shore. We report the results of a high-resolution seismic profiling of the western sector of La Fossa Caldera (Vulcano Island, Italy). Using a high-resolution vibrating source and both alternative acquisition and processing techniques, we were able to overcome most of the inconvenience caused by volcanic lithotypes. This study provides the subsurface distribution of volcanic deposits as well as the recognition of some significant intracaldera structures. We located a parasitic vent or hyaloclastite mound buried under La Fossa Caldera, which is dissipating CO 2 in an area where earthquakes have been recorded at about 1 km depth. Furthermore, the deformation pattern found at the southernmost part of the profile is consistent with a caldera collapse after a dome intrusion. The results suggest that the use of high-resolution vibrating sources combined with alternative seismic acquisition techniques and nonconventional processing could help to recover detailed information on the shallow structures of volcanic areas. Copyright 2009 by the American Geophysical Union
Environmental risk assesment of a shallow aquifer in "Piana Campana" Italy: a field comparison between seismic refraction and reflection methods
No full textEUROPEAN JOURNAL OF ENVIRONMENTAL AND ENGINEERING GEOPHYSIC
Seismic reflection data processing in active volcanic areas: an application to Campi Flegrei and Somma Vesuvius offshore (Southern Italy)
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
Seismic study of the Mesozoic carbonate basement around Mt. Somma-Vesuvius, Italy
No full textFifteen seismic reflection lines from AGIP surveys, in and around the Campanian Plain and Mt. Somma–Vesuvius (south Italy) have been interpreted. The attention has been focused to the horizon pertinent to the top of the Mesozoic carbonate sequence and the Quaternary faults dissecting it. As a matter of fact, both are very important elements for understanding the origin of the volcanic activity in the area, that often in the past, has been the topic of debates not supported by reliable data. In the study area, referring to the depth of the carbonate basement, comparison between the result achieved by the seismic prospecting and previous gravity studies has been made. It shows coherence in some areas but large discrepancy within others. Near the town of S. Anastasia, the gravity and seismic depth estimates differ as much as 1000 m or more. Furthermore, the seismic data show that the source of the greatest volcanic eruption in the area (the so-called `Campanian Ignimbrite') is probably not located in the Acerra depression, as suggested by other authors. A main NE–SW fault directed toward Vesuvius, considered as playing a primary role on volcanogenetic processes and previously recognised only offshore by marine seismic survey, has been now identified also inland using this new seismic information. The results presented here strengthen the hypothesis that Mt. Vesuvius is located at the crossing point of two regional Quaternary sets of fault heading NW–SE and NE–SW
High-resolution seismic profiling reveals faulting associated with the 1934 Ms 6.6 Hansel Valley earthquake (Utah, USA)
No full textThe 1934 Ms 6.6 Hansel Valley, Utah, earthquake produced an 8-km-long by 3-kmwide zone of north-south-trending surface deformation in an extensional basin within the easternmost Basin and Range Province. Less than 0.5 m of purely vertical displacement was measured at the surface, although seismologic data suggest mostly strike-slip faulting at depth. Characterization of the origin and kinematics of faulting in the Hansel Valley earthquake is important to understand how complex fault ruptures accommodate regions of continental extension and transtension. Here, we address three questions: (1) How does the 1934 surface rupture compare with faults in the subsurface? (2) Are the 1934 fault scarps tectonic or secondary features? (3) Did the 1934 earthquake have components of both strike-slip and dip-slip motion? To address these questions, we acquired a 6.6-km-long, high-resolution seismic profile across Hansel Valley, including the 1934 ruptures. We observed numerous eastand west-dipping normal faults that dip 40°- 70° and offset late Quaternary strata from within a few tens of meters of the surface down to a depth of ~1 km. Spatial correspondence between the 1934 surface ruptures and subsurface faults suggests that ruptures associated with the earthquake are of tectonic origin. Our data clearly show complex basin faulting that is most consistent with transtensional tectonics. Although the kinematics of the 1934 earthquake remain underconstrained, we interpret the disagreement between surface (normal) and subsurface (strike-slip) kinematics as due to slip partitioning during fault propagation and to the effect of preexisting structural complexities. We infer that the 1934 earthquake occurred along an ~3-km wide, off-fault damage zone characterized by distributed deformation along small-displacement faults that may be alternatively activated during different earthquake episodes
Accommodation, slip inversion, and fault segmentation in a province-scale shear zone from high-resolution, densely spaced wide-aperture seismic profiling, Centennial Valley, MT, USA
Full text linkWe acquired a ~9-km long, high-resolution reflection seismic profile in the Centennial Valley, Montana, to better understand the kinematics of basin bounding faults and their role in accommodating proposed right-lateral shear in the Northern Basin and Range adjacent to the Yellowstone hotspot. In pursuing these goals, our findings have also shed light on the development of hanging wall stratigraphy and seismic hazards for this part of the SW Montana seismic belt. Here we present the profile and a working interpretation that identifies fault inversion, and an oblique, anticlinal accommodation zone linking the Centennial and Lima Reservoir faults in the Centennial Valley. These interpretations are consistent with seismicity and GPS-geodetically observed right-lateral shear aligned with the Centennial Valley north of the Yellowstone hotspot. Data were acquired using dense, wide-aperture arrays and illuminate the subsurface stratigraphy and faults down to ~1200 m, showing that the basin is a half-graben with a southern depocenter driven by the listric geometry of the north-dipping Centennial fault. Reflectors onlap basement highs with growth geometry against these faults. Our interpretation of a bright basal reflection as the Timber Hill Basalt (~6 Ma) or related flow, is consistent with a late Miocene - Pliocene inception of the basin proposed by other research. We also note a small inversion structure that we interpret as local evidence of transpression in the shear zone. This transpression is part of the accommodation zone and seismogenic faults including the Lima Reservoir fault that has well-expressed Holocene surface ruptures a few kilometres west of the seismic line along the northern edge of the Centennial basin
High resolution seismic imaging in alpine environment by common reflection surface method
No full textIn alpine environment, alluvial fan architecture can reveal important information about the landscape geomorphic evolution and the climate change. The information about alluvial fan morphology and sedimentology can be obtained by a high-resolution geophysical approach. In this work, we acquired and processed a ~4 km long high-resolution seismic reflection profile across a representative transect of Val Venosta, over the Gadria fan, Eastern Alps, Italy, using non-conventional acquisition and processing approaches. We tested Dense-wide aperture arrays (DWA) and Common Reflection Surface stack (CRS) in a complex environment, in order to obtain seismic data with a quality and resolution adequate to: 1) study the internal reflective configuration of the fan; 2) image both the pattern of the bedrock below the valley and thickness of the sediment accumulation above it; 3) evaluate the geometrical relationships between the Gadria Fan and the Adige River sediments. By the analysis of our results, we can deduce that DWA seismic data in combination with high-resolution CDP/CRS processing can provide complimentary and low-cost information to aid the study of alluvial fans in alpine environments. © (2015) by the European Association of Geoscientists & Engineers (EAGE)
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