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Author |
Monteiller Vadim, Chevrot Sébastien, |
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Title |
How to make robust splitting measurements for single-station analysis and three-dimensional imaging of seismic anisotropy
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Type |
Journal Article |
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Year |
2010 |
Publication |
Geophysical Journal International |
Abbreviated Journal |
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Volume |
182 |
Issue |
1 |
Pages |
311 -328 |
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Abstract  |
We quantify errors on splitting intensity measurements produced by incoherent noise on horizontal components through a detailed analysis of synthetic seismograms and of SKS and SKKS waves recorded by four permanent broad-band stations. We find that these errors are quite significant, even on high-quality records, because the measurement procedure involves the comparison of radial and transverse components, which are both contaminated by noise. To decrease the level of noise in the data, it is thus recommended to average splitting intensities from waves coming from the same backazimuth. Alternatively, one can analyse stacked radial and transverse components after applying a Wiener filter, which standardizes the waveforms. This is found to be equivalent because the measure of splitting intensity is a linear process. The utilization of Wiener filters reduces variations of apparent splitting resulting from differences in frequency content of the waveforms. It is possible to determine splitting parameters (splitting delays and fast directions) from azimuthal variations of splitting intensity at a particular station. Tests on synthetic seismograms demonstrate that this approach gives unbiased and robust estimates of splitting parameters, in contrast to the Silver and Chan method, which only works on the rare records that have very large signals on their transverse components. The Wolfe and Silver method does not suffer from this limitation and gives the same results as the multichannel splitting intensity method. Analysis of splitting intensities at stations BDFB, BGCA, CAN and ERM gives fast directions that are generally in excellent agreement with those determined with the Wolfe and Silver method. However, at some stations, azimuthal variations of splitting intensities reveal features that are not well captured by the sinusoidal variation representing the average anisotropy beneath the station. This suggests that small-scale lateral variations of anisotropy are present in the subcontinental mantle, which remain to be imaged in detail.
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133 |
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0956-540X |
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yes |
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461 |
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Author |
Zalian C, Chadid M, Vernin J, Abe L, Agabi A, |
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Title |
Antarctica photometry of the Blazhko RR Lyrae star S Arae
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Journal Article |
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Year |
2015 |
Publication |
Monthly Notices of the Royal Astronomical Society |
Abbreviated Journal |
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Volume |
456 |
Issue |
1 |
Pages |
192-206 |
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Abstract |
We pursue the study of S Arae, an RRab Lyrae Blazho star, using unique, uninterrupted and accurate optical photometric data acquired from Antarctica at Dome C by PAIX – Photometer AntarctIca eXtraction – during 150 d. The PAIX data were analysed using both Period04 and PDM13. Besides a main pulsation period of 0.452 d and a modulation period of 47.264 d, three other significant frequencies were found. Multiplet patterns, up to the ninth order, were also extracted, showing a clear asymmetric structure. Following these results, a new approximation of the main-frequency harmonics amplitude decrease is suggested, replacing the usual exponential fit by a hyperbolic one. The physical properties of the Blazhko star, namely metallicity, temperature, mass, were obtained using a new approach based on the study of these parameters for each Blazhko phase. Finally, the PAIX data reveal a residual scatter that occurs during a small phase interval, 10 per cent of the pulsation period, corresponding to the phase of the main shock passage across the atmosphere. The position of the so-called main bump, corresponding to the shock resulting from the infalling atmosphere and the expanding photosphere, varies from one cycle to another and, moreover, around this main bump, two other bumps appear and vanish at different phases during a Blazhko cycle. Following these observations, we discuss the relation between the bump topology and the Blazhko period and give new insights for future Blazhko theoretical investigations.
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1096 |
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0035-8711 |
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yes |
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Serial |
6247 |
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Author |
Ciais P, Rayner P, Chevallier F, Bousquet P, Logan M, Peylin P, Ramonet M, |
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Title |
Atmospheric inversions for estimating CO2 fluxes: methods and perspectives
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Type |
Journal Article |
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Year |
2010 |
Publication |
Climatic Change |
Abbreviated Journal |
0165-0009 |
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Volume |
103 |
Issue |
1 |
Pages |
69-92 |
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Keywords |
Earth and Environmental Science, |
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Abstract |
We provide a review description of atmospheric inversion methods for the determination of fluxes of long-lived trace gases based on measurements of atmospheric concentration. Emphasis is given to technical aspects of inversion settings, which are crucial to inter-compare and understand inversion results. We briefly sketch the formalism used in such methods, then provide a summary of major currents in research and contemporary problems. Most attention is given to carbon dioxide (CO 2 ) which poses the threat of future climate change. Therefore, there is keen interest in better understanding where and when CO 2 emitted by the combustion of fossil fuels is reabsorbed by land ecosystems and oceans. Using the information contained in concentration fields observed from ground-based networks and from upcoming satellite observations in order to constrain the geographic distribution of surface fluxes is an inverse problem; it consists of finding a set of fluxes that optimally matches the observations available. We review the application of inverse methods to quantify the distribution of the sources and sinks of CO 2 at the surface of the Earth based on global measurements of atmospheric concentration and three-dimensional models of atmospheric transport. We describe the use of topdown atmospheric inversion methods in terms of numerical transport modeling and atmospheric observation networks, and detail some of the currently important issues in assigning uncertainties. |
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416 |
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Springer Netherlands |
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ISSN |
0165-0009 |
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yes |
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Call Number |
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Serial |
3127 |
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Author |
Alexander Kokhanovsky, Simon Gascoin, Laurent Arnaud, Ghislain Picard |
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Title |
Retrieval of Snow Albedo and Total Ozone Column from Single-View MSI/S-2 Spectral Reflectance Measurements over Antarctica |
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Journal |
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Year |
2021 |
Publication |
Remote Sensing |
Abbreviated Journal |
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Volume |
13 |
Issue |
21 |
Pages |
4404 |
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Keywords |
albedo inverse problems light scattering radiative transfer snow snow grain size |
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Abstract |
We proposed a simple algorithm to retrieve the total ozone column and snow properties (spectral albedo and effective light absorption path) using the high spatial resolution single–view MSI/S-2 measurements over Antarctica. In addition, the algorithm allows the retrieval of the snow grain size on a scale of 10–20 m. This algorithm should be useful for the understanding of intra-pixel total ozone and snow albedo variability in complement to satellite observations performed on a much coarser spatial resolution scale (0.3–1 km and even larger spatial scales). |
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1110 |
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Edition |
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ISSN |
2072-4292 |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
8305 |
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Author |
Lesur Vincent, Rother Martin, Wardinski Ingo, Schachtschneider Reyko, Hamoudi Mohamed, Chambodut Aude, |
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Title |
Parent magnetic field models for the IGRF-12GFZ-candidates
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Type |
Journal Article |
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Year |
2015 |
Publication |
Earth, Planets and Space |
Abbreviated Journal |
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Volume |
67 |
Issue |
1 |
Pages |
87-87 |
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Keywords |
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Abstract |
We propose candidate models for IGRF-12. These models were derived from parent models built from 10 months of Swarm satellite data and 1.5 years of magnetic observatory data. Using the same parameterisation, a magnetic field model was built from a slightly extended satellite data set. As a result of discrepancies between magnetic field intensity measured by the absolute scalar instrument and that calculated from the vector instrument, we re-calibrated the satellite data. For the calibration, we assumed that the discrepancies resulted from a small perturbing magnetic field carried by the satellite, with a strength and orientation dependent on the Sun’s position relative to the satellite. Scalar and vector data were reconciled using only a limited number of calibration parameters. The data selection process, followed by the joint modelling of the magnetic field and Euler angles, leads to accurate models of the main field and its secular variation around 2014.0. The obtained secular variation model is compared with models based on CHAMP satellite data. The comparison suggests that pulses of magnetic field acceleration that were observed on short time scales average-out over a decade. |
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139 |
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Springer |
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ISSN |
1343-8832 |
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Approved |
yes |
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Call Number |
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Serial |
6075 |
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Author |
Di Giacomo Domenico, Grosser Helmut, Parolai Stefano, Bormann Peter, Wang Rongjiang, |
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Title |
Rapid determination of Me for strong to great shallow earthquakes
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Type |
Journal Article |
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Year |
2008 |
Publication |
Geophys. Res. Lett. |
Abbreviated Journal |
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Volume |
35 |
Issue |
10 |
Pages |
L10308- |
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Keywords |
amplitude decay dunctions, readiated seismic energy, energy magnitude, 7219 Seismology: Seismic monitoring and test-ban treaty verification, 7215 Seismology: Earthquake source observations, 7203 Seismology: Body waves, |
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Abstract |
We propose a new rapid procedure for determining the energy magnitude Me for shallow events from broadband teleseismic P-wave signals within the distance range 20–98. To accomplish this task, we compute spectral amplitude decay functions for different periods using numerical simulations based on the reference Earth model AK135Q. By means of these functions, we correct the spectra of the teleseismic recordings for the propagation path effects, and calculate the radiated seismic energy E S , and hence Me. We use cumulative P-wave windows for simulating a real- or near real-time procedure and test it for 61 shallow earthquakes. The results show that our approach is able to provide a rapid and reliable Me determination within 7–15 minutes after the earthquake origin time, and is therefore suitable for implementation in rapid response systems.
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133 |
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AGU |
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ISSN |
0094-8276 |
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yes |
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Call Number |
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Serial |
2783 |
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Author |
Rochette P., Gattacceca J., Eisenlohr P. & Folco L. |
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Title |
In situ magnetic identification and classification of meteorites in Antarctica. |
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Journal Article |
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Year |
2004 |
Publication |
Lunar and planetary science |
Abbreviated Journal |
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Pages |
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Abstract |
We present the results of the use of magnetic methods (susceptibility, magnetic anomalies) applied to meteorite identification and partial classification. These methods were successfully tested during a meteorite collection expedition in Antarctica. |
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Programme |
412 |
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Thesis |
Bachelor's thesis |
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ISSN |
1540-7845 |
ISBN |
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Approved |
yes |
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Call Number |
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Serial |
3192 |
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Author |
Haydar Karaoğlu, Barbara Romanowicz |
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Title |
Global seismic attenuation imaging using full-waveform inversion: a comparative assessment of different choices of misfit functionals |
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Journal |
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Year |
2018 |
Publication |
Geophysical Journal International |
Abbreviated Journal |
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Volume |
212 |
Issue |
2 |
Pages |
807-826 |
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Keywords |
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Abstract |
We present the results of synthetic tests that aim at evaluating the relative performance of three different definitions of misfit functionals in the context of 3-D imaging of shear wave attenuation in the earth’s upper mantle at the global scale, using long-period full-waveform data. The synthetic tests are conducted with simple hypothetical upper-mantle models that contain Qμ anomalies centred at different depths and locations, with or without additional seismic velocity anomalies. To build synthetic waveform data sets, we performed simulations of 50 events in the hypothetical (target) models, using the spectral element method, filtered in the period range 60–400 s. The selected events are chosen among 273 events used in the development of radially anisotropic model SEMUCB-WM1 and recorded at 495 stations worldwide. The synthetic Z-component waveforms correspond to paths and time intervals (fundamental mode and overtone Rayleigh waves) that exist in the real waveform data set. The inversions for shear attenuation structure are carried out using a Gauss–Newton optimization scheme in which the gradient and Hessian are computed using normal mode perturbation theory. The three different misfit functionals considered are based on time domain waveform (WF) and waveform envelope (E-WF) differences, as well as spectral amplitude ratios (SA), between observed and predicted waveforms. We evaluate the performance of the three misfit functional definitions in the presence of seismic noise and unresolved S-wave velocity heterogeneity and discuss the relative importance of physical dispersion effects due to 3-D Qμ structure. We observed that the performance of WF is poorer than the other two misfit functionals in recovering attenuation structure, unless anelastic dispersion effects are taken into account in the calculation of partial derivatives. WF also turns out to be more sensitive to seismic noise than E-WF and SA. Overall, SA performs best for attenuation imaging. Our tests show that it is important to account for 3-D elastic effects (focusing) before inverting for Qμ. Additionally, we show that including high signal-to-noise ratio overtone wave packets is necessary to resolve Qμ structure at depths greater than 250 km. |
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Programme |
133 |
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Thesis |
Bachelor's thesis |
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ISSN |
0956-540X |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
7881 |
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Author |
Armelle Decaulne, Najat Bhiry, Julien Lebrun, Samuel Veilleux, Denis Sarrazin |
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Title |
Geomorphic evidence of Holocene slope dynamics on the Canadian shield – a study from Lac à l’Eau-Claire, western Nunavik |
Type |
Journal |
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Year |
2018 |
Publication |
Écoscience |
Abbreviated Journal |
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Volume |
0 |
Issue |
0 |
Pages |
1-15 |
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Keywords |
éboulis gélifraction Nunavik scree slope dynamics Talus |
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Abstract |
We present the results of a study of the morphometric properties of a talus slope in subarctic Quebec (Nunavik) using field-based methods, including geomorphological, granulometric and plant distribution surveys, and statistical analyses. Slope processes are currently active, despite the limited altitudinal difference between the apical-to-distal parts of the slope and the imminent depletion of the debris supply. The near-rectilinear long profiles of the talus highlight the distribution of debris across the slope and demonstrate that free-fall of rock fragments is not the only process operating (redistribution is higher in the westernmost profile, which exhibits a clear concave shape). The spatial distribution of vegetation covering the screes highlights the recent age of parts of the talus, showing that present-day processes are still active, although limited. The short remaining apical rockwall highlights the shortage of debris following deglaciation, as debris are mostly supplied by freeze-thaw processes to the talus, and are then reworked by other processes which need to be better defined in subsequent research. |
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Programme |
1148 |
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ISSN |
1195-6860 |
ISBN |
1195-6860 |
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yes |
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Call Number |
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Serial |
6778 |
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Author |
Armelle Decaulne, Najat Bhiry, Julien Lebrun, Samuel Veilleux, Denis Sarrazin |
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Title |
Geomorphic evidence of Holocene slope dynamics on the Canadian shield – a study from Lac à l’Eau-Claire, western Nunavik |
Type |
Journal |
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Year |
2018 |
Publication |
Écoscience |
Abbreviated Journal |
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Volume |
25 |
Issue |
4 |
Pages |
343-357 |
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Keywords |
éboulis gélifraction Nunavik scree slope dynamics Talus |
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Abstract |
We present the results of a study of the morphometric properties of a talus slope in subarctic Quebec (Nunavik) using field-based methods, including geomorphological, granulometric and plant distribution surveys, and statistical analyses. Slope processes are currently active, despite the limited altitudinal difference between the apical-to-distal parts of the slope and the imminent depletion of the debris supply. The near-rectilinear long profiles of the talus highlight the distribution of debris across the slope and demonstrate that free-fall of rock fragments is not the only process operating (redistribution is higher in the westernmost profile, which exhibits a clear concave shape). The spatial distribution of vegetation covering the screes highlights the recent age of parts of the talus, showing that present-day processes are still active, although limited. The short remaining apical rockwall highlights the shortage of debris following deglaciation, as debris are mostly supplied by freeze-thaw processes to the talus, and are then reworked by other processes which need to be better defined in subsequent research. |
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Programme |
1148 |
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1195-6860 |
ISBN |
1195-6860 |
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Approved |
yes |
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Call Number |
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Serial |
7428 |
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