[1] In November 2007 we conducted a water column and seafloor mapping study of the submarine volcanoes of the Aeolian Arc in the southern Tyrrhenian Sea aboard the R/V Urania. On 26 conductivity-temperature-depth casts and tows we measured temperature, conductivity, pressure, and light scattering and also collected discrete samples for helium isotopes, methane, and pH. The 3He/4He isotope ratio, an unambiguous indicator of hydrothermal input, showed a clear excess above background at 6 of the 10 submarine volcanoes surveyed. Marsili seamount had the highest anomaly, where the 3He/4He ratio reached a δ3He value of 23% at 610 m depth compared with background values of ∼5%. Smaller but distinct δ3He anomalies occurred over Palinuro, Enarete, Eolo, Sisifo, and Secca del Capo. Although hydrothermal emissions are known to occur offshore of some Aeolian subaerial volcanoes, and hydrothermal deposits have been sampled throughout the arc, our results are the first to confirm active discharge on Marsili, Enarete, Eolo, Sisifo, and Secca del Capo. Samples collected over Lametini, Filicudi North, Alicudi North, and Alcione had δ3He near the regional background values, suggesting either absence of, or very weak, hydrothermal activity on these seamounts. Hydrocasts between the volcanoes revealed a consistent δ3He maximum between 11% and 13% at 2000 m depth throughout the SE Tyrrhenian Sea. The volcanoes of the Aeolian arc and the Marsili back arc, all <1000 m deep, cannot contribute directly to this maximum. This deep 3He excess may be a remnant of tritium decay or may have been produced by an unknown deep hydrothermal source.
Seismic tomography can be used to image the spatial variation of rock properties within complex geological media such as volcanoes. Solfatara is a volcano located within the Campi Flegrei, a still active caldera, so it is of major importance to characterize its level of activity and potential danger. In this light, a 3D tomographic high-resolution P-wave velocity image of the shallow central part of Solfatara crater is obtained using first arrival times and a multiscale approach. The retrieved images, integrated with the resistivity section and temperature and the CO2 flux measurements, define the following characteristics: 1. A depth-dependent P-wave velocity layer down to 14 m, with Vp < 700 m/s typical of poorly-consolidated tephra and affected by CO2 degassing; 2. An intermediate layer, deepening towards the mineralized liquid-saturated area (Fangaia), interpreted as permeable deposits saturated with condensed water; 3. A deep, confined high velocity anomaly associated with a CO 2 reservoir. These features are expression of an area located between the Fangaia, water saturated and replenished from deep aquifers, and the main fumaroles, superficial relief of the deep rising CO2 flux. Therefore, the changes in the outgassing rate greatly affect the shallow hydrothermal system, which can be used as a "mirror" of fluid migration processes occurring at depth.
Ischia Island represents only the remnant of a once larger volcanic complex. To prove this hypothesis about 600 km of new marine geophysical data were analysed. Results reveal that the western offshore of the island consists of previously unreported E‐W and NE‐SW volcanic ridges that follow the regional structural patterns. The match between sea‐borne magnetic anomalies and bathymetric/seismic data indicates the presence of a large, cooled magmatic system with deeper intrusions along the NE‐SW direction. Some of the newly discovered submerged volcanoes are dissected by fault scarps that offset, with a strong vertical component, recentmost (possibly Holocene) marine and volcanoclastic deposits. Our data suggest the importance of regional tectonics (in particular along the NE‐SW trend) on the patterns of magma uprising and on the recent local deformation in the Neapolitan volcanic district.
Abstract The Vettore–Bove normal fault system in central Italy ruptured during the 2016 M W 6.5 Norcia earthquake causing extensive surface faulting. At the Pian Grande di Castelluccio hanging wall basin, along the southern section of the fault ruptured during the M W 6.5 mainshock, we performed a high‐resolution seismic reflection/refraction experiment aimed at (a) imaging the shallow pattern of the fault system, and (b) reconstructing the architecture of the continental infill. We collected three profiles for a total length of ∼8 km. We used a reflection processing flow and non‐linear refraction tomography to obtain migrated stack sections and P‐wave velocity images resolved down to the depth of the pre‐Quaternary substratum. The main profile in the northern part of the basin crosses the westernmost splays of the ruptured fault zone striking N150°–170°. Seismic imaging unravels a ∼1 km‐wide fault zone comprising three W‐throwing splays and subsidiary faults, which affect the continental infill and produce a minimum aggregate Quaternary throw of ∼400 ± 100 m. Recent deformation is localized in this part of the surveyed fault section, attesting active displacement accumulation of the Vettore–Bove fault system. The other profiles in the central‐southern part of the basin show additional faults, likely striking N20°–40° and which concurred to generate a ∼500 m‐deep depocenter. These faults were mostly active during an early extensional phase; however, one of them likely displaces shallow layers with a throw close to the resolution limit of seismic data (<10 m), suggesting activity in the Late Pleistocene.
We present a 2-D subsurface image of the Paganica Fault from a high-resolution refraction tomography and detailed geological investigation carried out across part of the northwestern segment of the 20-km-long Paganica–San Demetrio fault-system, and which was responsible of the 2009 April 6 Mw 6.1 L'Aquila earthquake (central Italy). We acquired two seismic profiles crossing the Paganica basin with a dense-wide aperture configuration. More than 30 000 P wave first-arrival traveltimes were input to a non-linear tomographic inversion. The obtained 250–300 m deep 2-D Vp images illuminate the shallow portion of the Paganica Fault, and depict additional unreported splays defining a complex half-graben structure. We interpret local thickening of low-Vp (<2400 m s−1) and intermediate-Vp (2600–3400 m s−1) regions as syn-tectonic clastic wedges above a high-Vp (3800–5000 m s−1) carbonate basement. These results are condensed in a 4.2-km-long section across the Paganica basin, clearly indicating that the Paganica Fault is a mature normal fault cutting the whole upper ∼10 km of the crust. We evaluate a minimum cumulative net displacement of 650 ± 90 m and a total heave of 530 ± 65 m accomplished by the Paganica Fault, respectively. In the conservative hypothesis that the extension started during the Gelasian (1.80–2.59 Ma), we obtain a minimum long-term slip-rate of 0.30 ± 0.07 mm yr−1 and an extension-rate of 0.25 ± 0.06 mm yr−1, respectively. Considering the regional averaged extensional field of ∼1 mm yr−1 obtained from geodetic and geological analyses at 104 yr timescale, we infer that the Paganica Fault accounts for ∼20 per cent of the NE-extension affecting this zone of the central Apennines axis due to the concurrent activity of other parallel normal fault-systems nearby (e.g. the Liri, Velino-Magnola, L'Aquila-Celano and Gran Sasso fault-systems).
Research Article| March 22, 2018 Postglacial evolution of a formerly glaciated valley: Reconstructing sediment supply, fan building, and confluence effects at the millennial time scale Francesco Brardinoni; Francesco Brardinoni † 1Department of Biological, Geological and Environmental Sciences, University of Bologna, Bologna, Italy †francesco.brardinoni@unibo.it Search for other works by this author on: GSW Google Scholar Vincenzo Picotti; Vincenzo Picotti 2Department of Earth Sciences, ETH Zürich, Zürich, Switzerland Search for other works by this author on: GSW Google Scholar Stefano Maraio; Stefano Maraio 1Department of Biological, Geological and Environmental Sciences, University of Bologna, Bologna, Italy3Centro di GeoTecnologie, University of Siena, San Giovanni Valdarno, Italy Search for other works by this author on: GSW Google Scholar Pier Paolo Bruno; Pier Paolo Bruno 4The Petroleum Institute, Department of Petroleum Geosciences, Abu Dhabi, UAE Search for other works by this author on: GSW Google Scholar Maurizio Cucato; Maurizio Cucato 5Provincia Autonoma di Bolzano, Ufficio Geologia e Prove Materiali, Cardano, Italy Search for other works by this author on: GSW Google Scholar Corrado Morelli; Corrado Morelli 5Provincia Autonoma di Bolzano, Ufficio Geologia e Prove Materiali, Cardano, Italy Search for other works by this author on: GSW Google Scholar Volkmar Mair Volkmar Mair 5Provincia Autonoma di Bolzano, Ufficio Geologia e Prove Materiali, Cardano, Italy Search for other works by this author on: GSW Google Scholar GSA Bulletin (2018) 130 (9-10): 1457–1473. https://doi.org/10.1130/B31924.1 Article history received: 06 Sep 2017 rev-recd: 12 Jan 2018 accepted: 16 Feb 2018 first online: 22 Mar 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Francesco Brardinoni, Vincenzo Picotti, Stefano Maraio, Pier Paolo Bruno, Maurizio Cucato, Corrado Morelli, Volkmar Mair; Postglacial evolution of a formerly glaciated valley: Reconstructing sediment supply, fan building, and confluence effects at the millennial time scale. GSA Bulletin 2018;; 130 (9-10): 1457–1473. doi: https://doi.org/10.1130/B31924.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We reconstruct the post–Last Glacial Maximum (LGM) evolution of the upper Adige River floodplain, Eastern Italian Alps. In particular, we are interested in constraining the time scales associated with fan building and understanding how the relevant sediment supply at tributary confluences has interacted with the Adige River to form the present landscape configuration. By combining high-resolution seismic imaging with drillhole data and radiocarbon dating, we show (i) that ∼80% of the valley fill was deposited in post-LGM times, (ii) that sediment evacuation from tributaries began with local deglaciation at the end of the Younger Dryas; and (iii) that tributary basin aspect and size, by controlling the local pattern of deglaciation, may have delayed fan building by up to two millennia. Debris-flow sediment supply from the Gadria-Strimm system drove the evolution of this valley segment between 12 and 6.25 k.y. B.P., first deflecting, then damming the course of the Adige River, forming a lake, and affecting the shape and size of the neighboring fans. Our data show an anisotropic development of the Gadria fan, with growth focused on the central and eastern portion of the fan between 10 and 8.5 k.y. B.P., followed by gradual lateral shifting toward west for about the next two millennia. The estimated sediment yield associated with the fan formation describes a debris flow–driven paraglacial sedimentary wave that conforms to the conceptual model originally proposed by Church and Ryder (1972), but never tested before in upland basins with empirical data. The wave lasted for ∼4 k.y. and around 9 k.y. B.P. peaked at ∼390,000 m3yr–1. At the valley profile scale, results suggest that similar fans functioned as effective sediment traps, which prevented, and still limit, fluvial reworking and valley floor incision. We argue that these geomorphic barriers, which have enhanced fragmentation of the valley long profile, with knickpoints located at major tributary fans, have delayed postglacial landscape recovery until today. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Range-bounding normal faults can presentsignificant challenges for seis- mic exploration. This is the case of the fault system bounding the Vallo di Diano, the largest intermountain basin in the southern Apennines seismic belt. Industry reflection profiles define the large-scale structure of the basin but barely image the shallow fault system due to unfavorable topographic and near-surface conditions along the foothills of the eastern range. We present two high-resolution (HR) wide-aperture profiles recorded attheeastern marginof thebasin acrossunreported scarpsthat affect Middle- Late Pleistocene alluvial fans and slope debris. The survey is aimed at identifying possible recent faulting across these challenging terrains and at understanding the re- lationship between shallow structures and the master range-bounding fault at depth. Common depth point processing of wide-aperture reflection data and first-arrival tra- vel-time tomography provide detailed images of the upper 200-300 m and sounding evidence of recent activity along previously unknown splays of the fault system. These splays dissect the Mesozoic limestone bedrock and alluvial-fan sequences, affecting theirdepositionalpattern.VeryhighresolutionVPandreflectivityimagesalsogivehints ofpossiblecoseismicsurfacefaultinginHolocenecolluvia.Theseresultshaverelevant implicationsfortheevaluationoftheseismogenicpotentialoftherange-boundingfault systemandforseismichazardassessmentofthedenselyurbanizedVallodiDianobasin. Online Material: Table of acquisition and data processing parameters, and figures showing schematic stratigraphy of the Vallo di Diano basin, restoration of fault dis- placement along the HR profile, and resolution of the P-velocity tomographic images for the VHR profile.
