130,464 research outputs found
Insights into active deformation in the Gulf of Cadiz from new 3-D seismic and high-resolution bathymetry data
No full textThe nature of active deformation in the Gulf of Cadiz is important for developing a better understanding of the interplate tectonics and for revealing the source of the 1755 Great Lisbon earthquake. New, high-resolution 3-D seismic data reveal a classic pull-apart basin that has formed on an east striking fault in the Southern Lobe of the Gulf of Cadiz accretionary wedge. Geometrical relationships between an array of faults and associated basins show evidence for both dextral and sinistral shear sense in the Southern Lobe. Strike-slip faulting within the lobe may provide a link between frontal accretion at the deformation front and extension and gravitational sliding processes occurring further upslope. Inception of the strike-slip faults appears to accommodate deformation driven by spatially variant accretion or gravitational spreading rates, or both. This implies that active deformation on strike-slip faults in the Southern Lobe is unrelated to the proposed modern inception of a transform plate boundary through the Gulf of Cadiz and underscores the importance of detailed bathymetric analysis in understanding tectonic processes
Polyphase deformations along the regional transect Squillace Basin-Crotone swell-Taranto basin-Apulian foreland: a Recent active collisional system in the northeastern Ionian Sea.
No full textThe Calabrian Arc (CA) is part of the most active seismic belt in Italy, and the Ionian Sea has been described as the last remaining segment of oceanic crust subduction in the central
Mediterranean. The thick sedimentary section of the African and Ionian plate has been scraped off from the descending plate, and piled up along thrust faults resulting in the emplacement of
a thick (up to 10 km) and about 200–300 km wide arcuate accretionary complex. In the study area, the accretionary wedge interfers with the Apulian foreland. Here, the continental crust of
the Apulian foreland is colliding with the suture zone of the Cretaceous-Paleogene Ligure-Piemontese ocean in Northern Calabria-Southern Apennines. This implies that, at least since
late Miocene to Recent, in the northeastern sector of the CA, a foreland basin system was generating, while to the SW , where the Ionian oceanic plate was subducting, thick forearc basins are present. The present work is aimed to analyze the geometry and tectono-stratigraphic evolution of this late Neogene foreland basin system along the transect Squillace Basin- Crotone swell-Taranto Basin-Apulian foreland based on the pre-stack depth migrated multichannel seismic line CROP M5, about 2000 Km of multichannel seismic reflection profiles collected in the past in the coastal region and 20 well logs available from: http://unmig.sviluppoeconomico.gov.it/videpi/. In this sector of the CA, the polyphase deformations are given by alternating
phases of extension and compression. NW-SE trending trascurrent fault zones affect the Late Miocene-Recent deposition and form along inherited and pre-Late Miocene deformation
zones. All these deformations produce variable and cross-cutting structural trends and many inversion structures active till very recently. Four structural domains will be described; from SW to NE, they are: 1) the Squillace basin; 2) the Crotone swell; 3) the Taranto Gulf; 4) the Apulian foreland. It is remarkable that polyphase deformation (i.e. alternating extension and
compression phases and the inversion structures) is common in all of the four domains, from the inner orogenic arc/wedge-top basin (Squillace basin and Crotone swell), to the foredeep basins
(Taranto basin) and the foreland area (Apulian foreland). This suggests that the northeastern sector of the CA is colliding and is starting to “accrete” the subducting Apulian plate about 100km east of the presumed continental-oceanic transition
Estimating internal wave spectra using constrained models of the dynamic ocean
No full textMulti-Channel Seismic method (MCS), with its ability to image events down to a lateral resolution of 10 m has been successfully applied to address questions in physical oceanography. However, to date, these analyses have overlooked an important detail; the imaged boundaries are dynamic and move on a timescale that can be resolved by the MCS method. An important step in understanding the effect of the movement is calibration against constrained models. We demonstrate in this paper that it is possible using careful interpolation to take high resolution models of dynamic water (160 m x 2 m spatial resolution and 15 min temporal resolution) and generate models for synthetic seismic simulations (20 m x 4 m spatial resolution and 20 sec temporal resolution). We show that moving water, when ignored, will distort analyses of wavenumber spectra estimated from seismic data since the relative movement of water masses and the seismic acquisition vessel will change the apparent slope of spectra. Citation: Vsemirnova, E., R. Hobbs, N. Serra, D. Klaeschen, and E. Quentel (2009), Estimating internal wave spectra using constrained models of the dynamic ocean, Geophys. Res. Lett., 36, L00D07, doi: 10.1029/2009GL039598
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Pre-stack depth migrated (PSDM) seismic transects across the Calabrian Arc: a Miocene-Pleistocene arcuate complex accretionary wedge in the Ionian sea
No full textThe Calabrian Arc (CA) is the most impressive arcuate feature of the Central Mediterranean sea and connects the E-W trending Sicilian Maghrebian belt with the NW-SE trending Southern Apennines defining the African-Eurasian plate boundary in the Ionian sea. The CA attained its geometry mostly in the interval between Middle-Late Miocene to Pleistocene and its evolution is related to the opening of the back-arc Tyrrhenian basin, in response to the SE retreat of the subduction zone caused by the sinking of the Mesozoic Ionian oceanic lithosphere along a steeply inclined Benioff plane.
In this geodynamic frame, the submerged portion of the CA is a key area to study subduction and collisional processes in detail. We reconstructed the regional architecture of the accretionary complex from MS-OGS lines and CROP deep seismic profiles acquired during 70s and 90s in the Ionian Sea. We preliminary re-processed MCS seismic data at ISMAR-BO, through a sequence that involves velocity analysis, Dip Move Out (DMO), velocity analysis after DMO, stack and time migration. Three CROP seismic lines were further processed at the Marine Geodynamics Department of the IFM-GEOMAR (Kiel) in the frame of the European EC-IHP project. We obtained full pre-stack depth-migrated (PSDM) seismic sections through an iterative migration procedure (The SIRIUS/GTX, Migpack software package) that uses seismic velocities constrained by focusing analysis and common reflection point gathers. We have thus obtained a very accurate velocity model that includes both lateral and vertical velocity variations in agreement with interpreted geological cross-sections.
The offshore external part of the CA is represented by a 300 km wide accretionary wedge, bordered by the Malta and Apulia Escarpments. Its active front extends southward close to the Medina Bank and is dissected by a prominent NNW-SSE striking tear fault located about 50 km E of the Malta Escarpment. The accretionary wedge, whose geometry and evolution are driven by the slow convergence between the African and the Eurasian Plates (estimated in 5 mm/yr or even <5 mm/yr), is characterized by a sub-horizontal décollement, and consists of African Plate sediments, scraped off from the thick (up to 10 km) Mesozoic and Cenozoic sedimentary cover of the descending plate and piled up along low angle thrust faults. The surface of the accretionary complex is marked by a gentle and irregular slope that sinks the water depth down to more than 4000 m. The outer portion of the slope (approximately from 3000 m to 4000 m of water depth down to the Ionian abyssal Plain) displays shallow strong deformation triggered by the presence of a very thick sequence of Messinian evaporites that have been accreted since Messinian. In this outer zone, the contractional deformation is driven by a detachment surface located at the base of the evaporites. The inner portion of the slope (approximately from 2000 m to 3000 m depth) exhibits a steeper topographic gradients associated with pronounced gravity anomalies and is the site of the pre-Messinian accretionary wedge. Here, the basal detachment cuts to deeper levels leading to the formation of complex thrust system, chaotic units and mud volcanoes. This region seems to be devoid of evaporites but thick accumulation of Messinian deposits occurs in restricted basins on top of the pre-Messinian wedge. Landward, between the upper slope and the onland Calabria (approximately at depths less than 2000 m or in the inner plateau of the CA), a backstop, made of Calabrian-affinity nappes, is partly overlain by back-thrust units of the pre-Messinian wedge and by the NE-SW trending Crotone-Spartivento fore-arc basin. Beneath most of the accretionary wedge the Mesozoic subducting crust is 18-20 km thick and seems to have an oceanic character, but quite anomalous if compared to typical oceanic crust because of velocity profiles and locally-preserved features typical of a passive margin
Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard
No full textActive gas venting occurs on the uppermost continental slope off west Svalbard, close to and upslope from the present-day intersection of the base of methane hydrate stability (BMHS) with the seabed in about 400 m water depth in the inter-fan region between the Kongsfjorden and Isfjorden cross-shelf troughs. From an integrated analysis of high-resolution, two-dimensional, pre-stack migrated seismic reflection profiles and multibeam bathymetric data, we map out a bottom simulating reflector (BSR) in the inter-fan region and analyze the subsurface gas migration and accumulation. Gas seeps mostly occur in the zone from which the BMHS at the seabed has retreated over the recent past (1975–2008) as a consequence of a bottom water temperature rise of 1°C. The overall margin-parallel alignment of the gas seeps is not related to fault-controlled gas migration, as seismic evidence of faults is absent. There is no evidence for a BSR close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted BMHS. While the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the BMHS and gas hydrate dissociation, the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted BMHS limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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