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  • 1
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    Modelling long-term seismic noise in various environments (2012)
    Oxford University Press
    Details
    Publication Date: 2012-09-08
    Description: SUMMARY The strongest seismic noise, called secondary microseisms, is generated by ocean wave interactions and we model this noise using the theory of Longuet-Higgins generalized to random ocean gravity waves. Noise sources are computed with an ocean wave model that takes into account coastal reflections. Variations of the source locations are consistent with seasonal variations of seismic noise spectra. Noise spectra are modelled over many years for stations representative of various environments such as continent, island and polar area to constrain, for each environment, the parameters involved in the modelling. For each station, we quantify the trade-off between ocean wave coastal reflection and seismic wave attenuation that both affect the amplitude of the seismic spectrum. We show their adjustment and the need, at some stations, for an extra parameter representing the three-dimensional (3-D) seismic wave propagation effects. The long-term analysis demonstrates the stability of the fitted parameters which can be used in future noise studies. The modelling enables to reproduce the frequency content and amplitude of the different noise peaks of seismic spectra. The strongest peaks are generated by deep ocean sources whereas coastal reflections generate numerous smaller sources that contribute to the background noise level. Coastal reflection effects can be neglected only for the Pacific island station PPT. The modelling also reproduces the peculiar noise spectrum variation in Antarctica (station DRV) which is related to the presence of sea ice around the stations.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
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    Chemical control of the charge state of nitrogen-vacancy centers in diamond (2011)
    American Physical Society (APS)
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    Publication Date: 2011-02-15
    Description: Author(s): M. V. Hauf, B. Grotz, B. Naydenov, M. Dankerl, S. Pezzagna, J. Meijer, F. Jelezko, J. Wrachtrup, M. Stutzmann, F. Reinhard, and J. A. Garrido We investigate the effect of surface termination on the charge state of nitrogen-vacancy (NV) centers, which have been ion-implanted a few nanometers below the surface of diamond. We find that, when changing the surface termination from oxygen to hydrogen, previously stable NV^{-} centers convert in... [Phys. Rev. B 83, 081304] Published Mon Feb 14, 2011
    Keywords: Semiconductors II: surfaces, interfaces, microstructures, and related topics
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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  • 3
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    Polarized Earth's ambient microseismic noise (2011)
    Wiley
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    Publication Date: 2011-07-22
    Description: We quantify, analyze, and characterize the frequency-dependent microseismic noise recorded by worldwide distributed seismic stations. Microseismic noise is generated through the interaction of ocean waves. It is the strongest ambient noise, and it is observed everywhere on Earth. We introduce a new approach which permits us to detect polarized signals in the time-frequency domain and which we use to characterize the microseismic noise. We analyze 7 years of continuous seismograms from the global GEOSCOPE network. Microseisms are dominated by Rayleigh waves, and we therefore focus on elliptically polarized signals. The polarized signals are detected in the time-frequency domain through a degree of polarization measure. We design polarization spectra and show that microseismic noise is more strongly polarized than noise in other frequency bands. This property is used to measure the directions of the polarized noise at individual stations as a function of time and frequency. Seasonal variations are found for the back azimuths and for the number of polarized signals at many stations. We show that the back azimuth directions are robust measurements that point toward the source areas computed from ocean wave models.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Numerical modeling of the Mount Meager landslide constrained by its force history derived from seismic data (2015)
    Wiley
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    Publication Date: 2015-02-21
    Description: We focus on the 6 August 2010 Mount Meager landslide that occurred in Southwest British Columbia, Canada. This 48.5 Mm 3 rockslide that rapidly changed into a debris flow was recorded by over 25 broadband seismic stations. We showed that the waveform inversion of the seismic signal making it possible to calculate the time history of the force applied by the landslide to the ground is very robust and stable, even when using only data from a single station. By comparing this force with the force calculated through numerical modeling of the landslide, we are able to support the interpretation of seismic data made using a simple block model [Allstadt, 2013]. However, our study gives different values of the friction coefficients involvedand more details about the volumes and orientation of the sub-events and the flow trajectory and velocity. Our sensitivity analysis shows that the characteristics of the released mass and the friction coefficients all contribute to the amplitude and the phase of the force. Despite this complexity, our study makes it possible to discriminate the best values of all these parameters. Our results suggest that comparing simulated and inverted forces helps to identify appropriate rheological lawsfor natural flows. We also show that, except for the initial collapse, peaks in the low-frequency force related to bends and runup over topography changes are associated with high frequency generation, possibly due to an increased agitation of the granular material involved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    A new highly penetrant form of obesity due to deletions on chromosome 16p11.2 (2010)
    Springer Nature
    Details
    Publication Date: 2010-02-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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