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Titre : GRACE gravitational signature of the 2011 Mw 9.0 Tohoku-oki earthquake Type de document : Article/Communication Auteurs : Isabelle Panet , Auteur ; Sylvain Bonvalot, Auteur ; Clément Narteau, Auteur ; Dominique Remy, Auteur ; Jean-Michel Lemoine, Auteur
Congrès : EGU 2018, General Assembly (8 - 13 avril 2018; Vienne, Autriche), Commanditaire Editeur : Munich [Allemagne] : European Geosciences Union EGU Année de publication : 2018 Collection : Geophysical Research Abstracts, ISSN 1607-7962 num. 20 Note générale : EGU2018-9714 Langues : Anglais (eng) Résumé : (auteur) We present a analysis of the 2011 Mw 9.0 Tohoku-oki earthquake gravity variations in a wide space-time window surrounding the event. We identify earthquake-related gravity signals by searching for transient variations near the time of the earthquake in GRACE-reconstructed time series of gravity gradients at different spatial scales. The gravity gradients are expressed in spherical frames rotated along the radial axis in order to enhance gravity variations according to different orientations. Applied to different sets of gravity field models, our analysis allows us to evidence anomalous gravity signals starting a few months before the rupture across the regional subduction system, which cannot be explained by mass redistributions from water cycle sources around Japan nor by GRACE striping. After the rupture, the gravity variations propagate far within the Pacific and the Philippine Sea plates interiors.We further test the presence of the pre-seismic signals by also applying a statistical analysis of the gravity gradient time series, without knowledge on the consecutive rupture. Our findings show that satellite gravity brings unique information to monitor major plate boundaries, which could be used in seismic hazard assessment. Numéro de notice : C2018-070 Thématique : POSITIONNEMENT Nature : Poster nature-HAL : Poster-avec-CL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91462
Titre : ITRF and seasonal station motions Type de document : Article/Communication Auteurs : Zuheir Altamimi Congrès : EGU 2018, General Assembly (8 - 13 avril 2018; Vienne, Autriche), Commanditaire Editeur : Munich [Allemagne] : European Geosciences Union EGU Année de publication : 2018 Collection : Geophysical Research Abstracts, ISSN 1607-7962 num. 20 Note générale : EGU2018-5103 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes descripteurs IGN] International Terrestrial Reference Frame
[Termes descripteurs IGN] variation saisonnièreRésumé : (auteur) By definition, the International Terrestrial reference Frame (ITRF) is a secular frame providing station positions at a reference epoch and linear velocities. Considering the requirements of some scientific applications, such as precise orbit determination, it becomes however important to develop corrective models that can be added to the ITRF coordinates to account for non-linear station motions, with respect to the Earth Center of Mass (CM). It is in this perspective that post-seismic deformation models were, for instance, provided with the ITRF2014 solution. The next most important non-linear effect to be taken into account would be seasonal station motions. Seasonal station motions were estimated during the ITRF2014 construction, independently for each space geodetic technique. No attempt was made, however, to combine the seasonal signals estimated for the different techniques, and seasonal corrections were therefore not provided with the ITRF2014 solution. We explore here the feasibility of deriving meaningful combined seasonal corrections in the CM frame using two possible approaches: (1) combining the seasonal signals estimated for the different techniques during the ITRF2014 construction, (2) accumulating the time series of input solutions from the four techniques all together, with properly weighted equality constraints on seasonal signals at co-location sites. Results of the two approaches will be confronted and analyzed in order to evaluate the level of consistency of the technique seasonal signals at co-location sites. Conclusion will be drawn on the possible ways of providing seasonal corrections consistent with the next ITRF release. Numéro de notice : C2018-063 Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComSansActesPubliés-Unpublished Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91397 ITRF2014 and Earth figure changes: evidence of global viscous relaxation in recent ice melting Earth’s response? / Laurent Métivier (2018)
Titre : ITRF2014 and Earth figure changes: evidence of global viscous relaxation in recent ice melting Earth’s response? Type de document : Article/Communication Auteurs : Laurent Métivier Congrès : EGU 2018, General Assembly (8 - 13 avril 2018; Vienne, Autriche), Commanditaire Editeur : Munich [Allemagne] : European Geosciences Union EGU Année de publication : 2018 Collection : Geophysical Research Abstracts, ISSN 1607-7962 num. 20 Note générale : EGU2018-7567 Langues : Anglais (eng) Résumé : (auteur) The latest solution of the International Terrestrial Reference Frame, entitled ITRF2014, presents particularly large vertical velocities across Greenland, South East Alaska and the Antarctic Peninsula, compared with the previous solution ITRF2008. We investigate here the geophysical origin of this evolution of the ITRF velocity field. From a selection of ITRF2014 GNSS vertical velocities we determine solid Earth figure changes and Earth’s geocenter motion at different dates. By exploring various geophysical models, we show that our estimations can be well explained by the deformation due to Glacial Isostatic Adjustment (GIA) and Recent Ice Melting (RIM). However, we also show that the obtained solid Earth oblateness is not consistent with J2-rate observations if we assume purely elastic RIM deformations.We explore here different rheological scenarios that may explain this discrepancy, including low viscosities in the asthenosphere and/or the D” layer, or possible phase transitions in the mantle transition zone. Numéro de notice : C2018-071 Thématique : POSITIONNEMENT Nature : Poster nature-HAL : Poster-avec-CL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91463
Titre : Mass redistributions of the 2011 Mw 9.0 Tohoku-oki earthquake from GRACE Type de document : Article/Communication Auteurs : Isabelle Panet Congrès : EGU 2018, General Assembly (8 - 13 avril 2018; Vienne, Autriche), Commanditaire Editeur : Munich [Allemagne] : European Geosciences Union EGU Année de publication : 2018 Collection : Geophysical Research Abstracts, ISSN 1607-7962 num. 20 Note générale : EGU2018-9770 Langues : Anglais (eng) Résumé : (auteur) Large-scale gravity variations associated with the deformations surrounding giant earthquakes are one way to probe the rheology of the Earth’s upper mantle. They can be described from the GRACE mission data at temporal scales of months to years, and spatial scales inbetween those of local and global plate dynamics. Here, we consider the case of the 2011 Mw 9.0 Tohoku-oki earthquake and perform a space-time analysis of the GRACE geoid time series in a wide domain surrounding the event. In addition to the near-epicentral signals, we evidence regional-scale gravity variations starting a few months before the rupture, and propagating far within the Pacific and Philippine Sea plate interiors after the event. The gravity signals suggests that the earthquake is part of a broadscale deformation migrating from depth to surface across the entire subduction system, involving precursory slab extension at midupper mantle depths. We discuss the implications of these results, which provide unique evidence for episodic mass transfers at timescales of months in-depth of the plates boundaries. Numéro de notice : C2018-055 Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComSansActesPubliés-Unpublished Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91466
Titre : Optimization of atomic clock locations for the geopotential determination from gravimetric network Type de document : Article/Communication Auteurs : Guillaume Lion Congrès : EGU 2018, General Assembly (8 - 13 avril 2018; Vienne, Autriche), Commanditaire Editeur : Munich [Allemagne] : European Geosciences Union EGU Année de publication : 2018 Collection : Geophysical Research Abstracts, ISSN 1607-7962 num. 20 Note générale : EGU2018-11444 Langues : Anglais (eng) Résumé : (auteur) Clock comparisons with an uncertainty at the xx in terms of relative frequency can provide a new kind of measurement to improve our knowledge of Earth’s gravity field and geoid. Indeed, instead of using state-of-the-art Earth’s gravitational field models to predict frequency shifts between distant clocks, they could permit to determine geopotential differences directly at a centimeter-level accuracy. In our previous work (Lion et al., 2017) dealing with the geopotential determination at high spatial resolution in mountainous regions (e.g. the Massif Central – France), we have pointed out that clock-based geodetic observable can provide useful information at spatial scales beyond what is available from satellites and they could be used to fill areas not covered by the gravity data on the ground. Our synthetic simulations have shown that adding few clock-based potential data to a gravimetric data set can significantly improve the quality of reconstruction of the geopotential. Therefore, it turns out there is a large variety of possible clock distribution allowing to reduce the reconstruction residuals (bias and standard deviation), with different locations and number of clocks. In this work, we have investigated ways to optimize clock locations from a gravimetric data set in the Massif Central region in order to know where to put them to minimize the residuals and improve further the determination of the geopotential. To do that, we have used a multi-objective genetic algorithm (GA). A GA is an evolutionary algorithm inspired by the idea of natural evolution. Starting from a random initial population, with different clock distributions, the algorithm selects clock locations with good chances of reproduction and reproduces the new generation of clock locations using operations such as crossover and mutation. The process depends on some objectives we want to reach in order to solve the optimization problem, and it is repeated several times for a given number of generations or until a solution considered as optimum is found. We show how GA can help to provide optimal solutions for a problem with a fixed and variable number of clock locations. We discuss the effect of different parameters, such as the way to define the objectives and the constrains of the problem, the effect of the coverage and the quality of the gravimetric data and possible applications. Numéro de notice : C2018-072 Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComSansActesPubliés-Unpublished Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91464 PermalinkPermalinkGeoscientific instrumentation methods and data systems (2012 -)
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