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Author |
L. Labrousse, S. Elvevold, C. Lepvrier, P. Agard |
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Title |
Structural analysis of high-pressure metamorphic rocks of Svalbard: Reconstructing the early stages of the Caledonian orogeny |
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2008 |
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Tectonics |
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27 |
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5 |
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Keywords |
blueschists Caledonian orogeny structural analysis Svalbard |
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Abstract |
The basement of Svalbard comprises several terranes that were assembled along NS-trending faults during the Caledonian orogeny. The NW and NE parts of Svalbard are considered to be derived from east Greenland, while SW Svalbard has affinities with Pearya, Ellesmere Island. High-pressure (HP) metamorphic rocks, such as eclogites and blueschists occur in west Svalbard and provide constraints on the history of the Caledonian convergence. The Motalafjella HP rocks display a geometry which is compatible with an initial dome structure sealed by Ordovician deposits. Retrogressed eclogites in Biscayarhalvøya appear in the uppermost unit of a nappe stack that formed in a constrictional deformation regime. The syncollisional exhumation of the eclogites was achieved before the deposition of Late Silurian conglomerates. The two field occurrences of HP rocks are interpreted with a detailed age review for the Svalbard terranes and a restoration of Svalbard paleogeography in the Devonian. We propose that the different tectonic events are part of a continuous Ordovician-Silurian orogenic sequence, predating the Scandian collision between Laurentia and Baltica. The closure of an ocean between Laurentia and a microplate was responsible for the formation and exhumation of the HP rocks of Motalafjella in the Ordovician, and later followed by the collision of the microplate with Laurentia in the Silurian. This orogenic phase can be considered as an equivalent of the Taconic orogeny in the Appalachians. The relative position of the Svalbard terranes and Greenland during this orogenic episode is constrained by strain directions measured in the field. |
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1944-9194 |
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yes |
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8237 |
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Author |
Cao A, Romanowicz B, |
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Title |
Constraints on shear wave attenuation in the Earth's inner core from an observation of PKJKP
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Year |
2009 |
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Geophysical Research Letters |
Abbreviated Journal |
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Volume |
36 |
Issue |
9 |
Pages |
L09301- |
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Keywords |
inner core, shear wave, quality factor, 3909 Elasticity and anelasticity, 5144 Wave attenuation, 7207 Core, 7203 Body waves, 8115 Core processes, |
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Based on the high quality broadband data from Gräfenberg array in Germany, we recently detected a reliable PKJKP phase, for which four kinds of evidence (travel time, slowness, back-azimuth, and comparison with a pseudo-liquid inner core model) were simultaneously provided. Also, for the first time, a clear waveform of PKJKP was observed. This gives us an unprecedented opportunity to put constraints on the shear wave attenuation in the earth's inner core using body waves. In order to minimize the potential influence of dispersion and phase shift caused by mantle heterogeneity, we adopt an envelope modeling approach. Our results show that the estimated Q from the shear phase PKJKP is significantly larger (315 ± 150) than that from normal mode observations. Because PKJKP samples the deep inner core, this indicates an increase of Q with depth in the inner core, in agreement with what is generally observed for Q.
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133 |
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1944-8007 |
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yes |
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99 |
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Zhang Yang, Ritsema Jeroen, Thorne Michael S, |
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Title |
Modeling the ratios of SKKS and SKS amplitudes with ultra-low velocity zones at the core-mantle boundary
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2009 |
Publication |
Geophysical Research Letters |
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Volume |
36 |
Issue |
19 |
Pages |
L19303- |
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Keywords |
core-mantle boundary, SKS waves, amplitudes, 0545 Modeling, 7203 Body waves, 7208 Mantle, |
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Abstract |
Between 105115° degrees, the SKS waveform is complicated by the formation of SPdKS, a wave that has segments of P diffraction along the core mantle boundary. While previous studies have primarily focused on the move-out of SPdKS from SKS, we analyze the concomitant reduction of the SKS amplitude. Long-period SKKS/SKS amplitude ratios present a coherent global pattern. SKKS/SKS is relatively large in North and South American recordings of deep Tonga-Fiji earthquakes but PREM-like in European recordings of earthquakes in South America and North American recordings of earthquakes in Indonesia. Modeling of SKKS/SKS indicate that Ultra-Low Velocity Zones (ULVZs), layers at the base of the mantle with a thickness of about 1020 km and a shear velocity reduction between 2030%, are required to explain high SKKS/SKS ratios and the early move-out of SPdKS.
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133 |
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1944-8007 |
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yes |
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Serial |
108 |
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Author |
Reymond D, Crusem R, Barriot J P, |
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Title |
Empirical approaches for fast robust inversion of seismic moment tensor from surface waves
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Journal Article |
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Year |
2010 |
Publication |
Geophysical Research Letters |
Abbreviated Journal |
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Volume |
37 |
Issue |
7 |
Pages |
L07307- |
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Keywords |
moment tensor, robust inversion, IRLS, 3260 Inverse theory, 7255 Surface waves and free oscillations, 7215 Earthquake source observations, |
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Abstract |
We present a method of robust inversion (also called IRLS: Iterative Reweighted Least Squares) which is surprisingly insensitive to outlier data points, as it discards automatically the aberrant points, without the necessity for careful human inspection and control of data quality. Different criteria based on residuals and signal-to-noise ratio are injected into the covariance matrix (acting like a weighting function), to perform the robust inversion using the iterative generalized discrete inverse method of Tarantola-Valette. From a practical point of view, this algorithm is used as the Preliminary Determination of Focal Mechanism (PDFM) method, which is a project for rapid estimation of source parameters of strong earthquakes in the context of tsunami warning. The input data to be inverted are spectra of long period surface waves, and as an output, the computed result is the seismic moment tensor, from which focal geometry of an earthquake, and principal stress axes are obtained. This method can be applied to any other method of non-linear (iterative) inversions confronted to the problem of outlier points polluting the data sets.
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133 |
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1944-8007 |
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yes |
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Call Number |
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Serial |
403 |
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Author |
Butler Rhett, Tsuboi Seiji, |
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Title |
Antipodal seismic observations of temporal and global variation at Earth's inner-outer core boundary
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Journal Article |
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Year |
2010 |
Publication |
Geophysical Research Letters |
Abbreviated Journal |
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Volume |
37 |
Issue |
11 |
Pages |
L11301- |
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Keywords |
antipode, Earth, core, 7207 Core, 7203 Body waves, 8115 Core processes, |
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Abstract |
We have found two pairs of earthquake doublets closely located antipodally on one diametral axis between Tonga-Algeria, and several other events on other axes. These doublets show significant correlation, and exhibit seismic phases traversing the Core that cannot be explained by a standard radial Earth model such as PREM. The antipodal waveform data are highly variable between axes. The observed variability of the waveforms indicates global variations in the structure above and below the Inner-Outer Core boundary region. We have found evidence for a regional low-velocity zone at the base of the Outer Core, corresponding with a decadal temporal variation (0.55 s) in seismic energy traversing the top of the Inner Core. We propose an antipodal seismic array to constrain and to provide further progress for the study of the Inner and Outer Core.
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133 |
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1944-8007 |
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yes |
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Serial |
448 |
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Author |
Obrebski M J, Ardhuin F, Stutzmann E, Schimmel M, |
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Title |
How moderate sea states can generate loud seismic noise in the deep ocean
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Journal Article |
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2012 |
Publication |
Geophysical Research Letters |
Abbreviated Journal |
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Volume |
39 |
Issue |
11 |
Pages |
L11601- |
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Keywords |
microseisms, polarization analysis, wave model, 4215 Climate and interannual variability, 4255 Numerical modeling, 4560 Surface waves and tides, 7220 Oceanic crust, 7255 Surface waves and free oscillations, |
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Abstract |
The location of oceanic sources of the micrometric ground displacement recorded at land stations in the 0.10.3 Hz frequency band (double frequency microseisms) is still poorly known. Here we use one particularly strong noise event in the Pacific to show that small swells from two distant storms can be a strong deep-water source of seismic noise, dominating temporarily the signals recorded at coastal seismic stations. Our interpretation is based on the analysis of noise polarization recorded all around the source, and the good fit achieved for this event and year-round between observed and modeled seismic data. The model further suggests that this is a typical source of these infrequent loud noise bursts, which supports previous inconclusive evidences of the importance of such sources. This new knowledge based on both modeling and observations will expand today's limits on the use of noise for climate studies and seismic imaging.
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133 |
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1944-8007 |
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yes |
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Call Number |
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Serial |
3831 |
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Author |
Chambodut A, Marchaudon A, Menvielle M, El-Lemdani Mazouz F, Lathuillére C, |
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Title |
The K-derived MLT sector geomagnetic indices
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Journal Article |
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Year |
2013 |
Publication |
GEOPHYSICAL RESEARCH LETTERS |
Abbreviated Journal |
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Volume |
40 |
Issue |
18 |
Pages |
4808-4812 |
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Keywords |
1530 Rapid time variations, 1555 Time variations: diurnal to decadal, 2784 Solar wind/magnetosphere interactions, 7954 Magnetic storms, geomagnetic indices, MLT sector (Magnetic Local Time sector), |
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Abstract |
New sub-auroral K-derived sector indices are proposed. They are based upon the K local geomagnetic activity indices from the planetary am network stations, and their derivation scheme draws directly from that of am indices. Four Magnetic Local Time (MLT) sectors are considered, leading to four different K-derived MLT-sector indices: the aσDawn (03-09 MLT), aσNoon (09-15 MLT), aσDusk (15-21 MLT) and aσMidnight (21-03 MLT) indices. They cover more than 4 solar cycles and, thus, allow robust statistical analysis. Statistical studies of the whole aσ data series and case studies for two geomagnetic storms are presented. These analyses clearly show that the four aσ have specific behaviors, and that it is possible to get insight into both the statistical properties of the physical processes responsible for the observed geomagnetic activity and contribution to the dynamics of a given storm. |
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139 |
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Bachelor's thesis |
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1944-8007 |
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yes |
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Call Number |
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Serial |
4336 |
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Author |
Grilli Roberto, Legrand Michel, Kukui Alexandre, Méjean Guillaume, Preunkert Suzanne, Romanini Daniele, |
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Title |
First investigations of IO, BrO, and NO2 summer atmospheric levels at a coastal East Antarctic site using mode-locked cavity enhanced absorption spectroscopy
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Journal Article |
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Year |
2013 |
Publication |
Geophysical Research Letters |
Abbreviated Journal |
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Volume |
40 |
Issue |
4 |
Pages |
791-796 |
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Keywords |
0365 Troposphere: composition and chemistry, Antarctica, Atmospheric oxidants, Radicals, |
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414 |
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Bachelor's thesis |
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1944-8007 |
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yes |
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4345 |
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Author |
Chambodut A, Marchaudon A, Menvielle M, El-Lemdani Mazouz F, Lathuillére C, |
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Title |
The K-derived MLT sector geomagnetic indices
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Journal Article |
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Year |
2013 |
Publication |
GEOPHYSICAL RESEARCH LETTERS |
Abbreviated Journal |
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Volume |
40 |
Issue |
18 |
Pages |
4808-4812 |
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Keywords |
1530 Rapid time variations, 1555 Time variations: diurnal to decadal, 2784 Solar wind/magnetosphere interactions, 7954 Magnetic storms, geomagnetic indices, MLT sector (Magnetic Local Time sector), |
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905 |
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Bachelor's thesis |
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1944-8007 |
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yes |
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4504 |
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Author |
Blain Stéphane, Renaut Sophie, Xing Xiaogang, Claustre Hervé, Guinet Christophe, |
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Title |
Instrumented elephant seals reveal the seasonality in chlorophyll and light-mixing regime in the iron-fertilized Southern Ocean
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Journal Article |
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Year |
2013 |
Publication |
Geophysical Research Letters |
Abbreviated Journal |
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Volume |
40 |
Issue |
24 |
Pages |
6368-6372 |
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Keywords |
Southern Ocean, climatology, chlorophyll, iron fertilization, 4855 Phytoplankton, 4805 Biogeochemical cycles, processes, and modeling, 4894 Instruments, sensors, and techniques, |
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109 |
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1944-8007 |
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4743 |
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