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Prato allo Stelvio - Prad am Stilfser Joch, Italy

Cigolini C.,University of Turin | Di Martino M.,National institute for astrophysics | Laiolo M.,University of Turin | Coppola D.,University of Turin | And 2 more authors.
Meteoritics and Planetary Science | Year: 2012

The twin Arkenu circular structures (ACS), located in the al-Kufrah basin in southeastern Libya, were previously considered as double impact craters (the "Arkenu craters")The ACS consist of a NE (Arkenu 1) and a SW structure (Arkenu 2), with approximate diameters of about 10kmThey are characterized by two shallow depressions surrounded by concentric circular ridges and silica-impregnated sedimentary dikes cut by local faultsOur field, petrographic, and textural observations exclude that the ACS have an impact originIn fact, we did not observe any evidence of shock metamorphism, such as planar deformation features in the quartz grains of the collected samples, and the previously reported "shatter cones" are wind-erosion features in sandstones (ventifacts)Conversely, the ACS should be regarded as a "paired" intrusion of porphyritic stocks of syenitic composition that inject the Nubia Formation and form a rather simple and eroded ring dike complexStock emplacement was followed by hydrothermal activity that involved the deposition of massive magnetite-hematite horizons (typical of iron oxide copper-gold deposits)Their origin was nearly coeval with the development of silicified dikes in the surroundingsPlugs of tephritic-phonolitic rocks and lamprophyres (monchiquites) inject the Nubian sandstone along conjugate fracture zones, trending NNW-SSE and NE-SW, that crosscut the structural axis of the basin. © 2012 The Meteoritical Society.

Matassoni L.,Fondazione Prato Ricerche | Fiaschi A.,Fondazione Prato Ricerche | Silengo M.C.,University of Pisa | Silengo M.C.,University of Florence | And 2 more authors.
Open Geosciences | Year: 2015

In this paperwe describe a microzonation survey carried out at a mountain Municipality (Piteglio, Northern Apennines). We complemented the available data by conducting 106 microtremor measurements for Horizontal-to- Vertical Spectral Ratio (HVSR) analysis. Most of the data concern the three major rural villages (Piteglio-Prataccio, Popiglio and Prunetta). Furthermore, we installed a field mobile seismic station at two of the major villages, in order to obtain earthquakes recordings. The HVSR analysis shows amplification effects due to eluvial or colluvial deposits overlying the seismic bedrock, even for areas previously mapped as bedrock outcrops. Most zones characterized by sandstone outcrops show peaked HVSR traces. This observation could be also interpreted in terms of a topographic effect. In contrast, areas characterised by chaotic materials (olistostrome) generally exhibit a flat HVSR. Other areas of seismic amplification were identified on alluvial and landslide deposits. Results byHVSR analysis arewell correlated with available data from geo-technical and geophysical surveys, thus allowing to invert HVSRs for the physical properties of the subsoil. Subsoil properties can thus be extrapolated also in areas for which only measurements of seismic noise are available. Moreover, noise HVSRs agree well with those from earthquakes recorded at the different selected sites. © 2015 L. Matassoni et al.

Piccinini D.,Italian National Institute of Geophysics and Volcanology | Piana Agostinetti N.,Dublin Institute for Advanced Studies | Saccorotti G.,Italian National Institute of Geophysics and Volcanology | Fiaschi A.,Fondazione Prato Ricerche | And 2 more authors.
Journal of Geodynamics | Year: 2014

Within the central Mediterranean geodynamic puzzle, the seismotectonic processes of the northern sector of the Apennines are still under debate. In this framework, we conducted a careful examination of seismic catalogues for five years of instrumental seismicity located in the eastern sector of the Tosco-Emiliano Apennines. In our study, we merge two separate seismic bulletins, derived from a small- and a large-aperture seismic network. The joint analysis of the seismic phases of both catalogues allows us to improve event locations and to assess their hypocentral depths. After re-location using a regional velocity model, we found that the spatial distribution of hypocenters follows characteristic patterns at the southwestern and northeastern sides of the chain. Such distribution exhibits a marked axial offset in correspondence of the Livorno-Sillaro Line (LSL), a NE-SW trending lithological discontinuity previously interpreted in terms of a transform zone. Basing on this evidence, and on additional observations related to the morphology of the area, we hypothesise the LSL to represent the shallow manifestation of a discontinuity affecting the whole lithospheric thickness, i.e. a incipient tear fault dislocating the subducting slab. © 2014 Elsevier Ltd.

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