2,240 research outputs found
Seismicity and active tectonics in the Alboran Sea, Western Mediterranean: Constraints from an offshore-onshore seismological network and swath bathymetry data
Seismicity and tectonic structure of the Alboran Sea were derived from a large amphibious seismological network deployed in the offshore basins and onshore in Spain and Morocco, an area where the convergence between the African and Eurasian plates causes distributed deformation. Crustal structure derived from local earthquake data suggests that the Alboran Sea is underlain by thinned continental crust with a mean thickness of about 20 km. During the 5 months of offshore network operation, a total of 229 local earthquakes were located within the Alboran Sea and neighboring areas. Earthquakes were generally crustal events, and in the offshore domain, most of them occurred at crustal levels of 2 to 15 km depth. Earthquakes in the Alboran Sea are poorly related to large-scale tectonic features and form a 20 to 40 km wide NNE-SSW trending belt of seismicity between Adra (Spain) and Al Hoceima (Morocco), supporting the case for a major left-lateral shear zone across the Alboran Sea. Such a shear zone is in accord with high-resolution bathymetric data and seismic reflection imaging, indicating a number of small active fault zones, some of which offset the seafloor, rather than supporting a well-defined discrete plate boundary fault. Moreover, a number of large faults known to be active as evidenced from bathymetry, seismic reflection, and paleoseismic data such as the Yusuf and Carboneras faults were seismically inactive. Earthquakes below the Western Alboran Basin occurred at 70 to 110 km depth and hence reflected intermediate depth seismicity related to subducted lithosphere
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Intraplate seamounts as a window into deep earth processes
Seamounts are windows into the deep Earth that are helping to
elucidate various deep Earth processes. For example, thermal and mechanical
properties of oceanic lithosphere can be determined from the flexing of oceanic
crust caused by the growth of seamounts on top of it. Seamount trails also are
excellent recorders of absolute plate tectonic motions and provide key insights into
the relationships among plate motion, plume motion, whole-Earth motion, and
mantle convection. And, because seamounts are created from the partial melts of
deep mantle sources, they offer unique glimpses into the chemical development and
heterogeneity of Earth’s deepest regions. Current research efforts focus on resolving
the fundamental differences between magmas generated by passive upwelling
from upper mantle regions and deep mantle plumes rising from the core-mantle
boundary, mapping the different modes of mantle plumes and mantle convection,
reconciling fixed and nonfixed mantle plumes, and understanding the prolonged
volcanic evolution of seamounts. The role of intraplate seamounts is pivotal to this
research, and we must collect vast amounts more geochemical and geophysical
data to advance our knowledge. These data needs leave the ocean wide open for
future seamount exploration
Dental Hygienists\u27 Knowledge of HIV, Attitudes Towards People with HIV and Willingness to Conduct Rapid HIV Testing
This study was aimed to determine the dental hygienists\u27 knowledge of HIV, attitudes towards people living with HIV and willingness to conduct rapid HIV testing
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Seamount subduction and earthquakes
Seamounts are ubiquitous features of the seafloor that form part of the fabric of oceanic crust. When a seamount enters a subduction zone, it has a major affect on forearc morphology, the uplift history of the island arc, and the structure of the downgoing slab. It is not known, however, what controls whether a seamount is accreted to the forearc or carried down into the subduction zone and recycled into the deep mantle. Of societal interest is the role seamounts play in geohazards, in particular, the generation of large earthquakes
Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic:Margin Uplift and Plate Tectonics
Tectonic models predict that following breakup, rift margins undergo only decaying thermal
subsidence during their postrift evolution. However, postbreakup stratigraphy beneath the NE Atlantic shelves
shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin
episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We
present a seismic reflection study from the Greenland Fracture Zone-East Greenland Ridge (GFZ-EGR) and the
NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the
termination of synrift deposition in the deep-sea basins and onset of (i) thermomechanical coupling across
the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across
the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermomechanical coupling
and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and
Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is
linked to onset of uplift and massive shelf progradation on the NE Greenland margin. Given an estimated
middle to late Miocene (~15–10Ma) age of the IMU, we speculate that the event is synchronous with uplift of
the east and west Greenland margins. The correlation between margin uplift and plate motion changes further
indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland
plume (a hot pulse) and/or by changes in intraplate stresses related to global tectonics
Using IMS hydrophone data for detecting submarine volcanic activity: Insights from Monowai, 26°S Kermadec Arc
Only little is known on active volcanism in the ocean. As eruptions are attenuated by seawater and fallout does not regularly reach the sea surface, eruption rates and mechanisms are poorly understood. Estimations on the number of active volcanoes across the modern seas range from hundreds to thousands, but only very few active sites are known. Monowai is a submarine volcanic centre in the northern Kermadec Arc, Southwest Pacific Ocean. During May 2011, it erupted over a period of five days, with explosive activity directly linked to the generation of seismoacoustic tertiary waves (‘T-phases’), recorded at three broadband seismic stations in the region.
We show, using windowed cross-correlation and time-difference-of-arrival techniques, that T-phases associated with this eruption are detected as far as Ascension Island, South Atlantic Ocean, where two bottom-moored hydrophone arrays are operated as part of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). We observe a high incidence of T-phase arrivals during the time of the eruption, with the angle of arrival stabilizing at the geodesic azimuth between the IMS arrays and Monowai. T-phases from the volcanic centre must therefore have propagated through the Sound Fixing And Ranging (SOFAR) channel in the South Pacific and South Atlantic Oceans and over a total geodesic range of approximately 15,800 km, one of the longest source-receiver distances of any naturally occurring underwater signal ever observed
Regulation of G protein-coupled receptors by palmitoylation and cholesterol
Due to their membrane location, G protein-coupled receptors (GPCRs) are subject to regulation by soluble and integral membrane proteins as well as membrane components, including lipids and sterols. GPCRs also undergo a variety of post-translational modifications, including palmitoylation. A recent article by Zheng et al. in BMC Cell Biology demonstrates cooperative roles for receptor palmitoylation and cholesterol binding in GPCR dimerization and G protein coupling, underlining the complex regulation of these receptors
Double Photoproduction off the Proton at Threshold
The reaction has been measured using the TAPS
BaF calorimeter at the tagged photon facility of the Mainz Microtron
accelerator. Chiral perturbation theory (ChPT) predicts that close to threshold
this channel is significantly enhanced compared to double pion final states
with charged pions. In contrast to other reaction channels, the lower order
tree terms are strongly suppressed in 2 photoproduction. The consequence
is the dominance of pion loops in the 2 channel close to threshold - a
result that opens new prospects for the test of ChPT and in particular its
inherent loop terms. The present measurement is the first which is sensitive
enough for a conclusive comparison with the ChPT calculation and is in
agreement with its prediction. The data also show good agreement with a
calculation in the unitary chiral approach.Comment: Submitted to PL
Photoproduction of pi0-mesons from nuclei
Photoproduction of neutral pions from nuclei (carbon, calcium, niobium, lead)
has been studied for incident photon energies from 200 MeV to 800 MeV with the
TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI
accelerator. Data were obtained for the inclusive photoproduction of neutral
pions and the partial channels of quasifree single pi0, double pi0, and
pi0pi+/- photoproduction. They have been analyzed in terms of the in-medium
behavior of nucleon resonances and the pion - nucleus interaction. They are
compared to earlier measurements from the deuteron and to the predictions of a
Boltzmann-Uehling-Uhlenbeck (BUU) transport model for photon induced pion
production from nuclei.Comment: 15 pages, 22 figures, accepted for publication in EPJ
Measurements of 12C(→γ,pp) photon asymmetries for Eγ= 200–450 MeV
The 12C (→γ ,pp) reaction has been studied in the photon energy range 200-450 MeV at the Mainz microtron MAMI-C, where linearly polarised photons were energy-tagged using the Glasgow-Mainz Tagged Photon Spectrometer and protons were detected in the Crystal Ball detector. The photon asymmetry Σ has been measured over a wider Eγ range than previous measurements. The strongest asymmetries were found at low missing energies where direct emission of nucleon pairs is expected. Cuts on the difference in azimuthal angles of the two ejected protons increased the magnitude of the observed asymmetries. At low missing energies the Σ data exhibit a strong angular dependence, similar to deuteron photodisintegration
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