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  • 1
    Online Resource
    Online Resource
    Effect of seismic source bandwidth on reflection sections to image water structure (2009)
    Associated volumes
    Details Availability
    In: Geophysical research letters, Hoboken, NJ : Wiley, 1974, 36(2009), 1944-8007
    In: volume:36
    In: year:2009
    In: extent:5
    Description / Table of Contents: The seismic reflection profile is the convolution of the seismic acquisition impulse response and the target impedance contrasts. In the ocean, these contrasts are mainly determined by the widths and gradients of the temperature transitions between the different water masses. Hence seismic oceanography profiles are sensitive to the frequency bandwidth of the seismic acquisition system. We tested a novel seismic source that allowed us to simultaneously profile the ocean with differing impulse responses. We show that frequencies ~20 Hz are best to delineate large impedance contrasts that occur over a vertical scale of several tens of meters whereas frequencies ~80 Hz image the boundaries of layers of around 10 m. We demonstrate a towed acquisition system that can operate from a research vessel to give a bandwidth from 10 to 120 Hz that could, if required, be modified to provide frequencies up to 200 Hz.
    Type of Medium: Online Resource
    Pages: 5 , graph. Darst
    ISSN: 1944-8007
    DOI: 10.1029/2009GL040215
    Language: English
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  • 2
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    Focal mechanisms for sub‐crustal earthquakes in the Gulf of Cadiz from a dense OBS deployment (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: An eleven‐month deployment of 25 ocean bottom seismometers provides an unprecedented opportunity to study low‐magnitude local earthquakes in the complex transpressive plate boundary setting of the Gulf of Cadiz, known for the 1755 Lisbon earthquake and tsunami. 36 relocated earthquakes (ML 2.2 to 4.8) concentrate at 40– 60 km depth, near the base of the seismogenic layer in ∼140 Ma old oceanic mantle lithosphere, and roughly align along two perpendicular, NNE‐SSW and WNWESE striking structures. First motion focal mechanisms indicate compressive stress for the cluster close to the northern Horseshoe fault termination which trends perpendicular to plate convergence. Focal mechanisms for the second cluster near the southern termination of the Horseshoe fault indicate a strike‐slip regime, providing evidence for present‐day activity of a dextral shear zone proposed to represent the Eurasia‐Africa plate contact. We hypothesize that regional tectonics is characterized by slip partitioning.
    Description: Published
    Description: L18309
    Description: 3.1. Fisica dei terremoti
    Description: 3.2. Tettonica attiva
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: oceanic lithospheric mantle ; focal mechanisms ; stress tensor inversion ; Gulf of Cadiz ; ocean bottom seismometer ; 1755 Lisbon earthquake ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Focal mechanisms for sub-crustal earthquakes in the Gulf of Cadiz from a dense OBS deployment (2010)
    In:  EPIC3Geophys. Res. Lett., 37, L18309
    Details
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Harmonizing European (and US?) OBS facilities (2015)
    In:  EPIC32015 Ocean Bottom Seismology forum, Vancouver, Washington, 2015-10-05-2015-10-06
    Details
    Publication Date: 2015-10-18
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 5
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    Coordinating OBS Parks in Europe (2012)
    In:  EPIC3EGU General Assembly, Vienna, Austria, 2012-04-22-2012-04-27
    Details
    Publication Date: 2019-07-17
    Description: Within Europe there are more than 380 Ocean Bottom Seismometers (OBS) distributed across 10 instrument parks in 6 countries. At least 120 of these OBS are wideband or broadband, over 260 can be deployed for at least 6 months at a time and 140 for at least one year. New parks are planned in two other European countries, which should add over 70 OBSs to this "fleet". However, these parks are under the control of individual countries or universities and hence to date this has made it difficult to organize large-scale experiments, especially for seismologists without marine experience. There has recently been an initiative to coordinate the use of these distributed instruments and their data products, to encourage large-scale experiments, possibly with onshore and offshore components, by seismologists who have not necessarily used OBSs before. The ongoing or planned developments include: Helping scientists with marine-specific formalities such as ship requests; clearer explanations of the noise floors of OBS instrumentation; improved clarity of instrument pricing and availability; standardized data output formats and data validation; and archiving in established seismological data centers. These efforts should allow improved experiment design in scientifically interesting regions with an offshore component and an easier, clearer way to organize large-scale, multi-country experiments. We will present details of this initiative to help organize large-scale experiments, the particularities of OBS sensors and marine deployments, the available instrumentation and new developments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
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    Coordinating European OBS Parks (2013)
    In:  EPIC3IAHS-IAPSO-IASPEI Joint Assembly, Gothenburg, Sweden, 2013-07-22-2013-07-26
    Details
    Publication Date: 2019-07-17
    Description: Within Europe, more than 380 Ocean Bottom Seismometers (OBS) are distributed across 10 instrument parks in 6 countries. At least 120 of these OBS are wideband or broadband, over 260 can be deployed for at least 6 months at a time and 140 for at least one year. New parks are planned in two other European countries, which should add over 70 OBSs to this "fleet". However, these parks are under the control of individual countries or universities and hence to date this has made it difficult to organize large-scale experiments, especially for seismologists without marine experience. We report on a recent initiative to coordinate the use of these distributed instruments and their data products, to encourage large-scale experiments, possibly with onshore and offshore components, by seismologists who have not necessarily used OBSs before. The ongoing or planned developments include: Helping scientists with marine-specific formalities such as ship requests; clearer explanations of the noise floors of OBS instrumenta- tion; improved clarity of instrument pricing and availability; standardized data output formats and data validation; and archiving in established seismological data centers. These efforts should allow improved experiment design in scientifically interesting regions with an offshore component and an easier, clearer way to organize large-scale, multi-country experiments. We will present details of this initiative to help organize large-scale experiments, the particularities of OBS sensors and marine deployments, the available instrumentation and new developments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 7
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    The structure of Mediterranean arcs: New insights from the Calabrian Arc subduction system (2021)
    Elsevier
    Details
    Publication Date: 2023-11-16
    Description: The formation of Cenozoic mountain belts in the Mediterranean realm was preceded by tens of millions of years of subduction, forming volcanic arcs, and frontal contractional systems. In addition, subduction usually involves slab rollback and formation of oceanic backarcs. Although such structure must have influenced the orogeny of Mediterranean mountain belts, no active analog has been mapped with modern crustal-scale seismic methods. Here, we study the entire Calabrian subduction system to map the structure resulting from Tethys lithosphere subduction and slab rollback, in a process that must be akin to that operating during a phase of the formation of the Mediterranean orogenic belts. We present a crustal-scale cross section of the entire Calabrian subduction system obtained from on- and off-shore wide-angle seismic data. The 2D P-wave velocity section shows spatially abrupt (〈5 km of profile distance) structural and petrological transitions from the Ionian sedimentary wedge and Calabrian arc, to the rifted NW Calabrian margin, where the Quaternary Aeolian arc is emplaced. The margin, then, transitions northwards into the Marsili backarc region, where exhumed mantle and localized volcanism occurred during its formation. This complex structure implies rapid temporal and spatial changes between magmatic and amagmatic processes, and between compressional and extensional regimes during the evolution of this subduction system. We find that some terranes involved in the Alpine orogeny share petrological and tectonic similarities with some domains of the Calabrian subduction system. Based on the results of this study we propose the Calabrian Arc system as an analog for the subduction structuration that preceded the formation of Alpine orogenic systems.
    Description: Published
    Description: 116480
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Coordinating OBS Parks in Europe (2012)
    In:  Geophysical Research Abstracts Vol. 14, EGU2012-9536, 2012
    Details
    Publication Date: 2020-02-12
    Description: Within Europe there are more than 380 Ocean Bottom Seismometers (OBS) distributed across 10 instrument parks in 6 countries. At least 120 of these OBS are wideband or broadband, over 260 can be deployed for at least 6 months at a time and 140 for at least one year. New parks are planned in two other European countries, which should add over 70 OBSs to this “fleet”. However, these parks are under the control of individual countries or universities and hence to date this has made it difficult to organize large-scale experiments, especially for seismologists without marine experience. There has recently been an initiative to coordinate the use of these distributed instruments and their data products, to encourage large-scale experiments, possibly with onshore and offshore components, by seismologists who have not necessarily used OBSs before. The ongoing or planned developments include: Helping scientists with marine-specific formalities such as ship requests; clearer explanations of the noise floors of OBS instrumentation; improved clarity of instrument pricing and availability; standardized data output formats and data validation; and archiving in established seismological data centers. These efforts should allow improved experiment design in scientifically interesting regions with an offshore component and an easier, clearer way to organize large-scale, multi-country experiments. We will present details of this initiative to help organize large-scale experiments, the particularities of OBS sensors and marine deployments, the available instrumentation and new developments.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/conferenceObject
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  • 9
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    Mantle exhumation and sequence of magmatic events in the Magnaghi–Vavilov Basin (Central Tyrrhenian, Italy): New constraints from geological and geophysical observations (2016)
    Elsevier
    In:  Tectonophysics, 689 . pp. 133-142.
    Details
    Publication Date: 2019-02-01
    Description: Highlights • A serpentinised peridotite basement is strongly supported by S-waves analysis • Depth dependent serpentinisation resembles to that observed at magma-poor margins. • Mantle exhumation was preceded by MOR-type magmatism and later intraplate volcanism. Summary The Tyrrhenian basin opened in the Neogene following the E–SE retreat of the Appenines–Calabrian subduction system and the subsequent back-arc extension of an orogenic crust. The resultant crustal structure includes a complex distribution of continental, back-arc magmatism, and mantle-exhumation domains. A clear example of this complex structure is found in the central and deepest part of the basin (i.e. Magnaghi–Vavilov sub-basin) where geophysical data supported that the bulk of the basement is composed of partially serpentinised peridotite representing exhumed mantle rocks, and intruded by basalts forming low ridges and volcanic edifices. However, those data sets cannot univocally demonstrate the widespread presence of serpentinised mantle rocks, let alone the percentage of serpentinisation. Here, we use S-wave arrivals and available geological information to further constrain the presence of mantle serpentinisation. Travel times of converted S-waves were used to derive the overall Vp/Vs and Poisson's ratio (σ), as well as S-wave velocity of the basement in the Magnaghi-Vavilov Basins. This analysis reveals Vp/Vs ≈ 1.9 (σ ≈ 0.3) that strongly supports a serpentinised peridotite forming the basement under the basins, rather than oceanic-type gabbro/diabase. P-wave velocity models is later used to quantify the amount of serpentinisation from fully serpentinised (up to 100%) at the top of the basement to 〈 10% at 5–7 km deep, with a depth distribution similar to continent–ocean Transition zones at magma-poor rifted margins. Seismic reflection profiles show normal faulting at either flank of the Magnaghi–Vavilov Basin that is potentially responsible for the onset of serpentinisation and later mantle exhumation. These results, together with basement sampling information in the area, suggests that the late stage of mantle exhumation was accompanied or soon followed by the emplacement of MOR-type basalts forming low ridges that preceded intraplate volcanism responsible for the formation of large volcanoes in the area.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.tecto.2016.01.041
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  • 10
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    The Gibraltar subduction: A decade of new geophysical data (2012)
    Elsevier
    In:  Tectonophysics, 574-575 . pp. 72-91.
    Details
    Publication Date: 2015-01-27
    Description: The Gibraltar arc, spans a complex portion of the Africa-Eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity. The seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold-and-thrust belt, have led to competing geodynamic models (delamination and subduction). Geophysical data acquired in the past decade provide a test for these models and support a narrow east-dipping, subduction zone. Seismic refraction studies indicate oceanic crust below the western Gulf of Cadiz. Tomography of the upper mantle reveals a steep, east-dipping high P-wave velocity body, beneath Gibraltar. The anisotropic mantle fabric from SKS splitting shows arc-parallel "fast directions", consistent with toroidal flow around a narrow, westward retreating subducting slab. The accompanying WSW advance of the Rif-Betic mountain belt has constructed a thick pile of deformed sediments, an accretionary wedge, characterized by west-vergent thrust anticlines. Bathymetric swath-mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided. Subduction has slowed significantly since 5 Ma, but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge. Three possible origins for this deformation are discussed; gravitational spreading, overall NW-SE convergence between Africa and Iberia and finally a WSW tectonic push from slow, but ongoing roll-back subduction. In the absence of arc volcanism and shallow dipping thrust type earthquakes, evidence in favor of present-day subduction can only be indirect and remains the object of debate. Continued activity of the subduction offers a possible explanation for great (M〉8.5) earthquakes known to affect the area, like the famous 1755 Great Lisbon earthquake. Recent GPS studies show SW motion of stations in N Morocco at velocities of 3-6 mm/yr indicating the presence of an independent block, a "Rif-Betic-Alboran" microplate, situated between Iberia and Africa
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.tecto.2012.08.038
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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