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Author |
Schimmel M, Stutzmann E, Gallart J, |
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Title |
Using instantaneous phase coherence for signal extraction from ambient noise data at a local to a global scale
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Type |
Journal Article |
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Year |
2011 |
Publication |
Geophysical Journal International |
Abbreviated Journal |
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Volume |
184 |
Issue |
1 |
Pages |
494-506 |
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Keywords  |
Time series analysis, Interferometry, Body waves, Surface waves and free oscillations, |
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Abstract |
Stacks of ambient noise cross-correlations are more and more routinely used to extract empirical Green's functions between station pairs. The success of the cross-correlations is due to waves which are recorded by both stations and that constructively sum at lag times which equal their propagation time between the station pair. Stacking cross-correlograms corresponding to different time spans improves the azimuthal noise coverage and further enhances the signals. Here we show how the instantaneous phase coherence can be used for a more efficient signal extraction from ambient noise cross-correlations. The instantaneous phase coherence is obtained by analytic signal processing and can be employed through the phase cross-correlation and/or through the time-frequency domain phase-weighted stack. The phase cross-correlation is more sensitive to waveform similarity but less sensitive to strong amplitude features than the conventional cross-correlation. The time-frequency domain phase-weighted stack cleans the ambient noise cross-correlograms by attenuating incoherent noise and permits an improved signal identification. We show that both approaches are powerful tools in the recovery of signals from ambient noise data and show examples where they improve the extraction of P and Rayleigh waves by considering local and global scale applications.
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133 |
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Blackwell Publishing Ltd |
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1365-246X |
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yes |
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Call Number |
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Serial |
3792 |
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Author |
Di Giacomo Domenico, Parolai Stefano, Bormann Peter, Grosser Helmut, Saul Joachim, Wang Rongjiang, Zschau Jochen, |
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Title |
Suitability of rapid energy magnitude determinations for emergency response purposes
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Type |
Journal Article |
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Year |
2010 |
Publication |
Geophysical Journal International |
Abbreviated Journal |
0956-540X |
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Volume |
180 |
Issue |
1 |
Pages |
361-374 |
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Keywords |
Time series analysis, Earthquake source observations, Body-waves, |
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Abstract |
It is common practice in the seismological community to use, especially for large earthquakes, the moment magnitude Mw as a unique magnitude parameter to evaluate the earthquake's damage potential. However, as a static measure of earthquake size, Mw does not provide direct information about the released seismic wave energy and its high frequency content, which is the more interesting information both for engineering purposes and for a rapid assessment of the earthquake's shaking potential. Therefore, we recommend to provide to disaster management organizations besides Mw also sufficiently accurate energy magnitude determinations as soon as possible after large earthquakes. We developed and extensively tested a rapid method for calculating the energy magnitude Me within about 1015 min after an earthquake's occurrence. The method is based on pre-calculated spectral amplitude decay functions obtained from numerical simulations of Green's functions. After empirical validation, the procedure has been applied offline to a large data set of 767 shallow earthquakes that have been grouped according to their type of mechanism (strike-slip, normal faulting, thrust faulting, etc.). The suitability of the proposed approach is discussed by comparing our rapid Me estimates with Mw published by GCMT as well as with Mw and Me reported by the USGS. Mw is on average slightly larger than our Me for all types of mechanisms. No clear dependence on source mechanism is observed for our Me estimates. In contrast, Me from the USGS is generally larger than Mw for strike-slip earthquakes and generally smaller for the other source types. For 67 per cent of the event data set our Me differs ±0.3 magnitude units (m.u.) from the respective Me values published by the USGS. However, larger discrepancies (up to 0.8 m.u.) may occur for strike-slip events. A reason of that may be the overcorrection of the energy flux applied by the USGS for this type of earthquakes. We follow the original definition of magnitude scales, which does not apply a priori mechanism corrections to measured amplitudes, also since reliable fault-plane solutions are hardly available within 1015 min after the earthquake origin time. Notable is that our uncorrected Me data show a better linear correlation and less scatter with respect to Mw than Me of the USGS. Finally, by analysing the recordings of representative recent pairs of strong and great earthquakes, we emphasize the importance of combining Mw and Me in the rapid characterization of the seismic source. They are related to different aspects of the source and may differ occasionally even more than 1 m.u. This highlights the usefulness and importance of providing these two magnitude estimates together for a better assessment of an earthquake's shaking potential and/or tsunamigenic potential.
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133 |
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Blackwell Publishing Ltd |
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1365-246X |
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yes |
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Call Number |
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Serial |
3224 |
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Author |
Thierry Anne-Mathilde, Brajon Sophie, Spée Marion, Raclot Thierry, |
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Title |
Differential effects of increased corticosterone on behavior at the nest and reproductive output of chick-rearing Adélie penguins
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Type |
Journal Article |
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Year |
2014 |
Publication |
BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY |
Abbreviated Journal |
Behav. Ecol. Sociobiol. |
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Volume |
68 |
Issue |
5 |
Pages |
721-732- |
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Keywords |
Time budget, Behavior, Glucocorticoid, Pygoscelis adeliae, Reproduction, Reproductive performances, |
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Abstract |
Glucocorticoid hormones (GCs) are important mediators of physiological and behavioral responses to stress. While many studies have evaluated the environmental, behavioral, or physiological correlates of GCs and their effects on reproductive performances, further work is needed to clarify the relationship between GCs and fitness. Assessing the effects of increased GC levels on specific behaviors of breeding animals should improve our understanding of how GCs affect parental care. In this experimental study, we measured the effects of an experimental increase in corticosterone (CORT, the main avian GC) levels on the behavior of free-living male Ad,lie penguins (Pygoscelis adeliae) within the colony, their reproductive output, and the indirect consequences of both on the behavior of their partners. We show that increased CORT levels in males decreased their foraging time at sea while increased their attendance at the nest, although their attentiveness toward the nest itself decreased. In addition, treated males spent more time on comfort behaviors (e.g., preening), vocalizing, and engaging in positive social interactions relative to controls. Treatment further affected the behavior of their partners, but not chick begging and feeding rates. Penguins with increased CORT levels also exhibited decreased reproductive output. Previous studies of Ad,lie penguins in different life history stages and environmental conditions suggest that the consequences of CORT treatment on reproductive performance are context-dependent. In addition to the potential delay in the effects of increased CORT levels on reproduction, this context dependence should be taken into account when studying the behavior of free-living animals in relation to stress-inducing situations.
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1091 |
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Springer Berlin Heidelberg |
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ISSN |
0340-5443 |
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yes |
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Call Number |
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Serial |
4996 |
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Author |
Sun Xinlei, Song Xiaodong, |
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Title |
Tomographic inversion for three-dimensional anisotropy of Earths inner core
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Type |
Journal Article |
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Year |
2008 |
Publication |
Physics of the Earth and Planetary Interiors |
Abbreviated Journal |
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Volume |
167 |
Issue |
12 |
Pages |
53-70 |
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Keywords |
Three-dimensional inner core anisotropy, Inner inner core, Three-dimensional ray tracing, |
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Abstract |
Seismological studies generally suggest that the Earths inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth. Previous body-wave studies of the inner core have relied on ray tracing or waveform modeling using one-dimensional (1D) models. Here we present non-linear tomographic inversions of the inner core anisotropy using three-dimensional (3D) ray tracing, spline parameterization, and a large collection of PKP differential travel times. We adapt a pseudo-bending ray tracing (PBR) method in spherical coordinates for seismic rays that traverse the inner core (PKP(DF) phase). The method iteratively perturbs each discontinuity point and continuous segment of the ray through 3D earth structure so that its travel time is minimum. The 3D anisotropic structure of the inner core is approximated to the first order as 3D heterogeneous (but isotropic) structure for a given ray. The data are corrected using a scaled mantle tomographic model. The inner core anisotropy model obtained has the following major features. (1) The model has strong hemispherical and depth variation. The isotropic velocity in the topmost inner core is greater in quasi-eastern hemisphere (QEH) (40160°E) than in quasi-western hemisphere (QWH) (other longitudes). The anisotropy is weak in QEH to the depth of 600700 km below the inner core boundary (ICB), while in QWH, the anisotropy increases at much shallower depth (about 100200 km below the ICB) to about 34%, then remains at about 24% throughout the rest of the inner core. (2) The anisotropy form changes abruptly (over a depth range of about 150 km) at the radius of about 600 km, slightly less than half of the inner core radius, forming a distinct inner inner core (IIC). The velocity in the IIC has maximums at equatorial and polar directions and minimum at an angle of about 40° from the equatorial plane. The velocity in the outer inner core (OIC), however, changes little for ray directions 040° from the equatorial plane. (3) Despite large variation of the anisotropy, the isotropic velocity (Voigt average) throughout the inner core is nearly uniform. The results suggest that the OIC is likely composed of the same type of iron crystals with uniform chemistry, but the IIC may be composed of a different type of crystal alignment, a different iron phase, or a different chemical composition. Our tests on model parameterization, mantle correction, and linear and non-linear inversion suggest the main features of our model are very robust. However, fine scale structures are likely to differ, particularly in the major transition zones, e.g., in the topmost QWH (isotropy to anisotropy), between OIC and IIC (change in the form of anisotropy), and between QEH and QWH in OIC (difference in anisotropy strength). Searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful. |
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133 |
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ISSN |
0031-9201 |
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yes |
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Call Number |
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Serial |
2804 |
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Author |
Thuillier, G.; Perrin, J.-M.; Lathuillère, C.; Hersé, M.; Fuller-Rowell, T.; Codrescu, M.; Huppert, F.; Fehrenbach, M. |
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Title |
Dynamics in the polar thermosphere after the coronal mass ejection of 28 October 2003 observed with the EPIS interferometer at Svalbard |
Type |
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 |
Issue |
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Pages |
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Keywords |
thermosphere; CME; neutral winds; EPIS; ESR; 0310 Atmospheric Composition and Structure: Airglow and aurora; 0358 Atmospheric Composition and Structure: Thermosphere: energy deposition; 7513 Solar Physics, Astrophysics, and Astronomy: Coronal mass ejections |
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Abstract |
The upper atmosphere dynamics in the polar cap is mainly driven by ion-drag momentum sources imposed by the mapping of magnetosphere convection into the thermosphere/ionosphere and by Joule and auroral particle heating. Auroral particles also enhance conductivity particularly in the middle and lower ionosphere. Changes in the magnetospheric energy and momentum sources can significantly modify the wind circulation during geomagnetic storms. To observe these effects, a Michelson interferometer has been installed in Svalbard to measure winds in the thermosphere. Prior to 30 October 2003, cloud cover over Svalbard rendered the conditions unfavorable for optical observation. However, meteorological conditions improved after this date to enable the thermospheric response to the 28 October coronal mass ejection to be made. During quiet geomagnetic conditions measured wind velocities were in good agreement with those predicted by the Horizontal Wind Model (HWM). During disturbed geomagnetic conditions, HWM tended to underestimate the observed velocities. Comparison of the wind observations with a physical model tended to show reasonable agreement during both the strongly driven and recovery phase of the storm. Although the physical model did not always capture the timing of the rapid changes in the wind response in the early phase of the storm, the amplitudes of the fluctuations were in good agreement. After the initial phase the physical model agreed well with both the timing and amplitude of the meridional and zonal wind fluctuations. The meridional wind component was also derived from the EISCAT Svalbard Radar ion velocity and was found to be in close agreement with the optical winds observations. |
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384 |
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Publisher |
American Geophysical Union |
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ISSN |
0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5585 |
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Author |
Hill-Falkenthal, J., A. Priyadarshi, J. Savarino, and M. H. Thiemens |
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Title |
Seasonal variations in 35S and Δ17O of sulfate aerosols on the Antarctic plateau |
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Journal Article |
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Year |
2013 |
Publication |
Journal of Geophysical Research: Atmospheres |
Abbreviated Journal |
J. Geophys. Res. Atmos. |
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The first reported seasonal Δ17O anomaly in sulfate aerosols and measurements of radioactive 35SO42− activities collected from Dome C, Antarctica, are reported. Δ17O values exhibit minima during summer (as low as 0.91‰) when tropospheric oxidation patterns are dominated by OH/H2O2 mechanisms. Significant enrichment during autumn and spring is observed (up to 2.40‰) as ozone oxidation increases in the troposphere relative to summer and both stratospheric sources and long-range transport become more significant to the total sulfate budget. An unexpected decrease in Δ17O is seen as winter progresses. This decline is concluded to potentially arise due to a reduction in vertical mixing in the troposphere or linked to variations in the long-range transport of sulfur species to Antarctica. 35SO42− activities exhibit maxima during summer (up to 1219 atoms 35S/m3) that correlate with the peak in stratospheric flux and minima during winter (as low as 146 atoms 35S/m3) when the lack of solar radiation substantially reduces photochemical activity. It is shown that 35S offers the potential to be used as an additional tracer to study stratospheric and tropospheric interactions and is used to estimate stratospheric input of sulfur (combination of SO2 and SO42−). Stratospheric sulfur input produces maxima during summer/autumn with an upper limit of 5.5 ng/m3 and minima during winter/spring with an upper limit of 1.1 ng/m3. From these results, it is concluded that the variation in Δ17O is more reliant upon shifts in tropospheric oxidation mechanisms and long-range transport than on changes in the stratospheric flux. |
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1011 |
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ISSN |
2169-8996 |
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yes |
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Call Number |
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Serial |
4471 |
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Author |
Delille D., Coulon F. & Pelletier E. |
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Title |
Effects of temperature warming during a bioremediation study of natural and nutrient amended hydrocarbon contaminated sub-Antarctic soils. |
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Journal Article |
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Year |
2004 |
Publication |
Cold regions science and technology |
Abbreviated Journal |
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Volume |
40 |
Issue |
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Pages |
61-70 |
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Keywords |
Temperature ; Soil petroleum hydrocarbon ; Bioremediation ; Antarctica |
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Abstract |
Although petroleum contamination is recognized as a significant threat to polar environments, documented research on the environmental consequences of terrestrial spills in cold regions is still scarce. Full-scale in situremediation of petroleum-contaminated soils has not yet been used in Antarctica, partly because it has long been assumed that air and soil temperatures are too low for an effective biodegradation. To test this assumption, the effects of temperature on the hydrocarbon mineralization rate have been quantified during a field pilot study carried out on artificially contaminated sub-Antarctic soils. The field study was initiated in December 2000 on two selected soils of the Grande Terre (Kerguelen Archipelago, 69°42'E-49°19'S). The first site supported an abundant vegetal cover, while the second one was a desert soil exempt of plant material. Two series of five experimental plots (0.75 x 0.75 m) were settled firmly into each of the studied soils. Each plot received 500 ml of diesel fuel or Arabian light crude oil, and half of them were covered with a black plastic sheet. All the plots were sampled on a regular basis over a 2-year period. Under natural sub-Antarctic conditions, the field tests revealed that up to 95% of total hydrocarbons were degraded within 1 year, indicating that low temperatures (0-7 °C) can still allow oil biodegradation ty indigenous microorganisms. Soil coverage induced a small but permanent increase of the temperature in the surface soil of 2 °C (annual mean) and favored the degradation of alkanes over aromatics. The present observations increase the number of possible scenarios involving controlled temperature design and effects in future in situ bioremediation strategies in sub-Antarctic soils. |
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193 |
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ISSN |
0165-232X |
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yes |
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2912 |
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Author |
Hétérier V, David B, De Ridder C, Rigaud T, |
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Title |
Ectosymbiosis is a critical factor in the local benthic biodiversity of the Antarctic deep sea
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Journal Article |
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Year |
2008 |
Publication |
Mar Ecol Prog Ser |
Abbreviated Journal |
Mar. Ecol. Prog. Ser. |
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Volume |
364 |
Issue |
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Pages |
67-76 |
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Keywords |
Symbiosis · Species diversity · Species abundance · Null models · Cidaroids · Weddell Sea |
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Abstract |
In deep-sea benthic environments, competition for hard substrates is a critical factor in the distribution and diversity of organisms. In this context, the occurrence of biotic substrates in addition to mineral substrates may change the characteristics of sessile fauna. We tested this hypothesis at different localities of the Weddell Sea (Antarctica) by studying the diversity of ectosymbionts living on the spines of cidaroids (echinoids). The presence of cidaroids promoted a higher total specific richness and increased sessile species abundance, but did not change the diversity. Analyses of species distribution suggested that the cidaroids are a favourable habitat for sessile organisms, compared to rocks, but are colonized by relatively specialist sessile species, leaving the unfavourable rock habitat to more generalist species. Therefore, our study highlights the role of some living organisms, such as cidaroids, as key species increasing Antarctic benthic deep-sea species richness through the niche they provide to symbiotic species. |
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Programme |
1124 |
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ISSN |
0171-8630 |
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yes |
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Call Number |
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Serial |
2823 |
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Author |
Qin Yilong, Capdeville Yann, Maupin Valerie, Montagner Jean-Paul, Lebedev Sergei, Beucler Eric, |
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Title |
SPICE benchmark for global tomographic methods
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Type |
Journal Article |
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Year |
2008 |
Publication |
Geophysical Journal International |
Abbreviated Journal |
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Volume |
175 |
Issue |
2 |
Pages |
598-616 |
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Keywords |
Surface waves and oscillations, Seismic anisotropy, Seismic tomography, Computational seismology, |
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Abstract |
The existing global tomographic methods result in different models due to different parametrization, scale resolution and theoretical approach. To test how current imaging techniques are limited by approximations in theory and by the inadequacy of data quality and coverage, it is necessary to perform a global-scale benchmark to understand the resolving properties of each specific imaging algorithm. In the framework of the Seismic wave Propagation and Imaging in Complex media: a European network (SPICE) project, it was decided to perform a benchmark experiment of global inversion algorithms. First, a preliminary benchmark with a simple isotropic model is carried out to check the feasibility in terms of acquisition geometry and numerical accuracy. Then, to fully validate tomographic schemes with a challenging synthetic data set, we constructed one complex anisotropic global model, which is characterized by 21 elastic constants and includes 3-D heterogeneities in velocity, anisotropy (radial and azimuthal anisotropy), attenuation, density, as well as surface topography and bathymetry. The intermediate-period (>32 s), high fidelity anisotropic modelling was performed by using state-of-the-art anisotropic anelastic modelling code, that is, coupled spectral element method (CSEM), on modern massively parallel computing resources. The benchmark data set consists of 29 events and three-component seismograms are recorded by 256 stations. Because of the limitation of the available computing power, synthetic seismograms have a minimum period of 32 s and a length of 10 500 s. The inversion of the benchmark data set demonstrates several well-known problems of classical surface wave tomography, such as the importance of crustal correction to recover the shallow structures, the loss of resolution with depth, the smearing effect, both horizontal and vertical, the inaccuracy of amplitude of isotropic S-wave velocity variation, the difficulty of retrieving the magnitude of azimuthal anisotropy and so on. The synthetic data set can be used to validate and calibrate new processing methodologies and has been made available to the scientific community at the Institut de Physique du Globe de Paris (IPGP) website (). Any group wishing to test their tomographic algorithm is encouraged to download the synthetic data.
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133 |
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Publisher |
Blackwell Publishing Ltd |
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1365-246X |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
2810 |
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Author |
Yano Tomoko, Tanimoto T, Rivera L, |
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Title |
The ZH ratio method for long-period seismic data: inversion for S-wave velocity structure
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Type |
Journal Article |
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Year |
2009 |
Publication |
Geophysical Journal International |
Abbreviated Journal |
0956-540X |
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Volume |
179 |
Issue |
1 |
Pages |
413-424 |
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Keywords |
Surface waves and free oscillations, Seismic tomography, Wave propagation, |
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Abstract |
The particle motion of surface waves, in addition to phase and group velocities, can provide useful information for S-wave velocity structure in the crust and upper mantle. In this study, we applied a new method to retrieve velocity structure using the ZH ratio, the ratio between vertical and horizontal surface amplitudes of Rayleigh waves. Analysing data from the GEOSCOPE network, we measured the ZH ratios for frequencies between 0.004 and 0.05 Hz (period between 20 and 250 s) and inverted them for S-wave velocity structure beneath each station. Our analysis showed that the resolving power of the ZH ratio is limited and final solutions display dependence on starting models; in particular, the depth of the Moho in the starting model is important in order to get reliable results. Thus, initial models for the inversion need to be carefully constructed. We chose PREM and CRUST2.0 in this study as a starting model for all but one station (ECH). The eigenvalue analysis of the least-squares problem that arises for each step of the iterative process shows a few dominant eigenvalues which explains the cause of the inversion's initial-model dependence. However, the ZH ratio is unique in having high sensitivity to near-surface structure and thus provides complementary information to phase and group velocities. Application of this method to GEOSCOPE data suggest that low velocity zones may exist beneath some stations near hotspots. Our tests with different starting models show that the models with low-velocity anomalies fit better to the ZH ratio data. Such low velocity zones are seen near Hawaii (station KIP), Crozet Island (CRZF) and Djibuti (ATD) but not near Reunion Island (RER). It is also found near Echery (ECH) which is in a geothermal area. However, this method has a tendency to produce spurious low velocity zones and resolution of the low velocity zones requires further careful study. We also performed simultaneous inversions for volumetric perturbation and discontinuity-depth perturbation. While its formulation and inversion were straightforward, there seemed to be a difficult trade-off problem between volumetric perturbation and discontinuity-depth perturbation.
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Programme |
133 |
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Campaign |
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Thesis |
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Publisher |
Blackwell Publishing Ltd |
Place of Publication |
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Original Title |
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Edition |
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ISSN |
1365-246X |
ISBN |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
2922 |
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