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JJ. Leveque, A. Maggi, A. Souriau, G. Wittlinger |
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Title |
CASE-IPY: autonomous seismic stations newly deployed on the East Antarctic Plateau. |
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Conference - International - Poster |
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2010 |
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EGU General Assembly, Vienna, 2010 |
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906 |
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Bachelor's thesis |
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yes |
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91 |
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Author |
A. Maggi, JJ. Lévêque, M. Bes de Berc, JY. Thoré, G. Wittlinger, V. Farra
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Title |
Seismology on ice plateaus : practical lessons learned from Concordia station (CCD) and the CASE-IPY experiment. |
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Conference - International - Poster |
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2010 |
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ESC General Assembly, Montpellier, 2010 |
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906 |
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yes |
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102 |
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Maggi A., Leveque JJ, Thore, JY, Bes de Berc, M., Bernard, A., Danesi, S. Morelli, A., Delladio, A., Sorrentino, D., Stutzmann, E. and the GEOSCOPE team. |
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Title |
Concordia CCD – A Geoscope station in continental Antarctica |
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Conference - International - Poster |
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Year |
2010 |
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EOS, Transactions, American Geophysical Union |
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906 |
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yes |
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3015 |
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Grob M, Maggi A, Stutzmann E, |
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Title |
Observations of the seasonality of the Antarctic microseismic signal, and its association to sea ice variability
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Journal Article |
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Year |
2011 |
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Geophys. Res. Lett. |
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38 |
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11 |
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L11302- |
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Keywords |
microseisms, sea, seismic noise, seismology, 0750 Cryosphere: Sea ice, 7299 Seismology: General or miscellaneous, 9310 Geographic Location: Antarctica, |
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Seismic noise spectra at all seismic stations display two peaks in the 1–20 s period band, called primary and secondary microseisms. They are caused by the coupling of ocean waves into Rayleigh waves. At most locations, microseismic power is greater during local winter (when nearby oceans are stormier) than local summer. This tendency is reversed for stations in Antarctica, where growth of local winter sea ice seems to impede microseism generation in near coastal areas. A decade of continuous data from coastal seismic stations in Antarctica show systematic seasonality in microseismic signal levels, and demonstrate associations with both broad-scale and local sea-ice conditions. Primary microseisms are known to be generated at the coast and the modulation that we observe can be associated with sea-ice variations both in the vicinity of the station and along other Antarctic coasts. The similar modulation of short-period secondary microseisms corroborates their mostly near-coastal origin, while the continued presence of long-period secondary microseisms suggests more distant source regions. These observations could be used to extend the monitoring of climate variability prior to the availability of satellite-derived climate indicators.
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906 |
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AGU |
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0094-8276 |
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yes |
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3292 |
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Maxime Bes de Berc, Jean-Jacques Lévêque, Alessia Maggi, Jean-Yves Thoré, Diego Sorrentino, Alberto Delladio, Stefania Danesi, Andrea Morelli
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Title |
Calibrating broad-band seismometers in the extreme cold : Application to the observatory station CCD (Concordia, DomeC, Antarctica).
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Conference - International - Communication |
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2011 |
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EOS, Transactions, American Geophysical Union |
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906 |
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yes |
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3293 |
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Author |
A Maggi |
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Title |
Pourquoi installer des stations sismiques en Antarctique? in Cap sur les Pôles, 100 questions sur les mondes polaires, F Lemarchand, MF André and F Rémy (Eds.) |
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2011 |
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906 |
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yes |
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1855 |
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Author |
Wittlinger Gérard, Farra Véronique |
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Title |
Observation of low shear wave velocity at the base of the polar ice sheets: evidence for enhanced anisotropy
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Journal Article |
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Year |
2012 |
Publication |
Geophysical Journal International |
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Volume |
190 |
Issue |
1 |
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391 -405 |
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Abstract |
We analyse seismic data from the broad-band stations located on the Antarctic and Greenland ice sheets to determine the large-scale seismic parameters of the polar ice sheets. The P-to-S converted waves at the ice/rock interface and inside the ice sheets and their multiples (the P receiver functions) are used to estimate the in situ P velocity Vp and the P-to-S velocity ratio Vp/Vs of the polar ice. The thickness of the whole ice layer is precisely known either from radio echo soundings or from ice core drillings allowing thus an accurate determination of Vp and Vp/Vs. At some places in and near the Wilkes Basin, a sedimentary layer is probably squeezed between the ice and the bedrock. We find that the polar ice caps have a two-layer structure, the upper layer of variable thickness about 2/3 of the total thickness with velocities very close to the ice standard values and the lower layer preserving a standard Vp but with about 25 per cent smaller shear wave velocity and a more or less constant thickness. The shear-velocity drop in the lower layer may be the evidence of a strong anisotropy induced by preferred orientation of ice crystals and by fine layering of soft and hard ice layers. A large variation of ice viscosity with depth is therefore expected and heterogeneous flowing of the polar ice sheet. This heterogeneous flowing may invalidate the use at great depth of the ice dating models based on monotonic layer thinning.
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906 |
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Bachelor's thesis |
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0956-540X |
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yes |
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3828 |
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Author |
Souriau Annie, Rivera Luis, Maggi Alessia, Lévêque Jean-Jacques, |
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Title |
Seismic attenuation in the eastern Australian and Antarctic plates, from multiple ScS waves
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Journal Article |
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Year |
2012 |
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Geophysical Journal International |
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Volume |
190 |
Issue |
1 |
Pages |
569 -579 |
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The attenuation of seismic shear waves in the mantle beneath the eastern Australian and Antarctic plates is analysed using a large data set of multiple ScSn waves, reflected n times at the core-mantle boundary and (n-1) times at the surface. The data are the transverse components of deep earthquakes from the subduction zones north and east of Australia, recorded at stations in Antarctica, Australia, Indonesia, New Caledonia and New Zealand. The data are filtered with narrow bandpass filters at five frequencies in the range 0.013-0.040 Hz. The ScSn+1/ScSn amplitude ratios of successive ScS phases are compared to the ratios computed for synthetic seismograms for the same paths and same focal mechanisms, to eliminate the effects of source radiation and geometric attenuation. The synthetic seismograms are computed from a summation of toroidal modes for the 1-D reference model PREM. The observed to computed spectral ratios appear consistent for similar paths. They reveal that the attenuation is not frequency dependent, that the contribution of scattering to attenuation is low, and that the PREM model is a valuable reference model for the study region at the considered frequencies. An inversion of the data at 0.026Hz is performed to retrieve the quality factor Q in the upper mantle, in regions defined using a priori constraints inferred from seismic shear velocities. Q values close to those of PREM are found beneath the Australian and Antarctic cratons, lower values beneath the Eastern Australian Phanerozoic margin, and very low values beneath the oceanic region between Australia and Antarctica, where ridges and a triple junction are present. The Australian-Antarctic Discordance along the South Indian ridge appears as an exception with a Q value close to those of stable continents. The highest Q values are found beneath the subduction zones, a feature which is not apparent in global attenuation models possibly because of its narrow lateral extension, and because it extends at depths larger than those sampled by surface waves. Despite limitations due to the uneven distribution of the ScSn bounce points at the surface and to the difficulty of collecting a large number of high quality data, our approach appears very promising. It is complementary to the more widely used determination of seismic attenuation using surface waves because it provides increased depth coverage, and a broader spectral coverage. It therefore has a considerable potential in future investigations of mantle structure and dynamics.
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906 |
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0956-540X |
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4165 |
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Author |
Verhoeven, O.; Rivoldini, A.; Vacher, P.; Mocquet, A.; Choblet, G.; Menvielle, M.; Dehant, V.; Van Hoolst, T.; Sleewaegen, J.; Barriot, J.-P.; Lognonné, P. |
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Title |
Interior structure of terrestrial planets: Modeling Mars' mantle and its electromagnetic, geodetic, and seismic properties |
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Journal Article |
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Year |
2005 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
110 |
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Keywords |
internal structure; Mars; network science; 5430 Planetary Sciences: Solid Surface Planets: Interiors; 6225 Planetary Sciences: Solar System Objects: Mars; 3672 Mineralogy and Petrology: Planetary mineralogy and petrology |
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Abstract |
We present a new procedure to describe the one-dimensional thermodynamical state and mineralogy of any Earth-like planetary mantle, with Mars as an example. The model parameters are directly related to expected results from a geophysical network mission, in this case electromagnetic, geodetic, and seismological processed observations supplemented with laboratory measurements. We describe the internal structure of the planet in terms of a one-dimensional model depending on a set of eight parameters: for the crust, the thickness and the mean density, for the mantle, the bulk volume fraction of iron, the olivine volume fraction, the pressure gradient, and the temperature profile, and for the core, its mass and radius. Currently, available geophysical and geochemical knowledge constrains the range of the parameter values. In the present paper, we develop the forward problem and present the governing equations from which synthetic data are computed using a set of parameter values. Among all Martian models fitting the currently available knowledge, we select eight candidate models for which we compute synthetic network science data sets. The synergy between the three geophysical experiments of electromagnetic sounding, geodesy, and seismology is emphasized. The stochastic inversion of the synthetic data sets will be presented in a companion paper. |
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905;907 |
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Bachelor's thesis |
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American Geophysical Union |
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0148-0227 |
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yes |
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IPEV @ Thierry.Lemaire @ |
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5567 |
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Author |
Thébault, E.; Mandea, M.; Schott, J.J. |
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Modeling the lithospheric magnetic field over France by means of revised spherical cap harmonic analysis (R-SCHA) |
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Journal Article |
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2006 |
Publication |
Journal of geophysical research-atmospheres |
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J. Geophys. Res. |
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111 |
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regional modeling; France; magnetic field; 1517 Geomagnetism and Paleomagnetism: Magnetic anomalies: modeling and interpretation; 1545 Geomagnetism and Paleomagnetism: Spatial variations: all harmonics and anomalies; 0545 Computational Geophysics: Modeling |
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We have recently proposed the revised spherical cap harmonic analysis (R-SCHA) modeling technique. The new mathematical functions represent faithfully the spatial variations of potential fields in a restricted area. In this paper, we tackle the inverse problem and outline the efficiency of the new basis functions with respect to real magnetic data. Processing simultaneously repeat stations, observatory, aeromagnetic, and CHAMP satellite data provides our first vector lithospheric field model over France, which extends from surface to 500 km of altitude. The magnetic field is represented with a minimum horizontal spatial representation of 40 km at the mean Earth radius. The magnetic lithospheric map consistency is confirmed with a comparison to known geological features. The model variation with altitude also suggests that the major French magnetic anomaly, the Paris basin anomaly, is produced by a deep-rooted geological structure. These results demonstrate the superiority of regional modeling over global modeling for delineating small-scale details in the lithospheric field. In view of forthcoming satellite missions, like Swarm, the revised spherical cap harmonic analysis method will help to accurately represent the lithospheric field for more detailed geological interpretations. |
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905;139 |
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American Geophysical Union |
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0148-0227 |
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IPEV @ Thierry.Lemaire @ |
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5617 |
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