280 research outputs found
The critical earthquake concept applied to mine rockbursts with time-to-failure analysis
We report new tests of the critical earthquake concepts performed on
rockbursts in deep South African mines. We extend the concept of an optimal
time and space correlation region and test it on the eight main shocks of our
catalog provided by ISSI. In a first test, we use the simplest signature of
criticality in terms of a power law time-to-failure formula. Notwithstanding
the fact that the search for the optimal correlation size is performed with
this simple power law, we find evidence both for accelerated seismicity and for
the presence of logperiodic behavior with a prefered scaling factor close to 2.
We then propose a new algorithm based on a space and time smoothing procedure,
which is also intended to account for the finite range and time mechanical
interactions between events. This new algorithm provides a much more robust and
efficient construction of the optimal correlation region, which allows us the
use of the logperiodic formula directly in the search process. In this
preliminary work, we have only tested the new algorithm on the largest event on
the catalog. The result is of remarkable good quality with a dramatic
improvement in accuracy and robustness. This confirms the potential importance
of logperiodic signals. Our study opens the road for an efficient implemention
of a systematic testing procedure of real-time predictions.Comment: 22 pages, 32 figure
An extraterrestrial trigger for the Early Cretaceous massive volcanism? Evidence from the paleo-Tethys Ocean
The Early Cretaceous Greater Ontong Java Event in the Pacific Ocean may have covered ca. 1% of the Earth's surface with volcanism. It has puzzled scientists trying to explain its origin by several mechanisms possible on Earth, leading others to propose an extraterrestrial trigger to explain this event. A large oceanic extraterrestrial impact causing such voluminous volcanism may have traces of its distal ejecta in sedimentary rocks around the basin, including the paleo-Tethys Ocean which was then contiguous with the Pacific Ocean. The contemporaneous marine sequence at central Italy, containing the sedimentary expression of a global oceanic anoxic event (OAE1a), may have recorded such ocurrence as indicated by two stratigraphic intervals with 187Os/188Os indicative of meteoritic influence. Here we show, for the first time, that platinum group element abundances and inter-element ratios in this paleo-Tethyan marine sequence provide no evidence for an extraterrestrial trigger for the Early Cretaceous massive volcanism
Evidence for the return of subducted continental crust
Author Posting. © Nature Publishing Group, 2007. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 448 (2007): 684-687, doi:10.1038/nature06048.Substantial quantities of terrigenous sediments are known to enter the
mantle at subduction zones, but little is known about their fate in the mantle.
Subducted sediment may be entrained in buoyantly upwelling plumes and returned
to the earth’s surface at hotspots, but the proportion of recycled sediment in the
mantle is small and clear examples of recycled sediment in hotspot lavas are rare.
We report here remarkably enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures
(up to 0.720830 and 0.512285, respectively) in Samoan lavas from three dredge
locations on the underwater flanks of Savai’i island, Western Samoa. The
submarine Savai’i lavas represent the most extreme 87Sr/86Sr isotope compositions
reported for ocean island basalts (OIBs) to date. The data are consistent with the
presence of a recycled sediment component (with a composition similar to upper
continental crust, or UCC) in the Samoan mantle. Trace element data show similar
affinities with UCC—including exceptionally low Ce/Pb and Nb/U ratios—that
complement the enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures. The
geochemical evidence from the new Samoan lavas radically redefines the
composition of the EM2 (enriched mantle 2) mantle endmember, and points to the
presence of an ancient recycled UCC component in the Samoan plume
Pre-eruptive magmatic processes re-timed using a non-isothermal approach to magma chamber dynamics
Open Source PaperThis work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise
in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. The attached file is the published version of the article
Antiretroviral-naive and -treated HIV-1 patients can harbour more resistant viruses in CSF than in plasma
Objectives The neurological disorders in HIV-1-infected patients remain prevalent. The HIV-1 resistance in plasma and CSF was compared in patients with neurological disorders in a multicentre study. Methods Blood and CSF samples were collected at time of neurological disorders for 244 patients. The viral loads were >50 copies/mL in both compartments and bulk genotypic tests were realized. Results On 244 patients, 89 and 155 were antiretroviral (ARV) naive and ARV treated, respectively. In ARV-naive patients, detection of mutations in CSF and not in plasma were reported for the reverse transcriptase (RT) gene in 2/89 patients (2.2%) and for the protease gene in 1/89 patients (1.1%). In ARV-treated patients, 19/152 (12.5%) patients had HIV-1 mutations only in the CSF for the RT gene and 30/151 (19.8%) for the protease gene. Two mutations appeared statistically more prevalent in the CSF than in plasma: M41L (P = 0.0455) and T215Y (P = 0.0455). Conclusions In most cases, resistance mutations were present and similar in both studied compartments. However, in 3.4% of ARV-naive and 8.8% of ARV-treated patients, the virus was more resistant in CSF than in plasma. These results support the need for genotypic resistance testing when lumbar puncture is performe
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