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From space to lithosphere: inversion of the GOCE gravity gradients. Supply to the Earth’s interior study / Matthieu Plasman in Geophysical journal international, vol 223 n° 1 (October 2020)  

Public [article]  inGeophysical journal international > vol 223 n° 1 (October 2020) . - pp 398 - 419 Titre : From space to lithosphere: inversion of the GOCE gravity gradients. Supply to the Earth’s interior study Type de document : Article/Communication Auteurs : Matthieu Plasman, Auteur ; Christel Tiberi, Auteur ; Cécilia Cadio, Auteur ; Anita Thea Saraswati, Auteur ; Gwendoline Pajot-Métivier , Auteur ; Michel Diament , Auteur Année de publication : 2020 Projets : 3-projet - voir note / Article en page(s) : pp 398 - 419 Note générale : bibliographie TOSCA project financing (PIGGS project) Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] anomalie de pesanteur [Termes IGN] données GOCE [Termes IGN] géophysique interne [Termes IGN] gradient de gravitation [Termes IGN] gravimétrie spatiale [Termes IGN] lithosphère [Termes IGN] problème inverse Résumé : (auteur) The emergence of high resolution satellite measurements of the gravitational field (GOCE mission) offers promising perspectives for the study of the Earth’s interior. These new data call for the development of innovant analysis and interpretation methods. Here we combine a forward prism computation with a Bayesian resolution approach to invert for these gravity gradient data configuration. We apply and test our new method on satellite data configuration, that is 225 km height with a global and homogeneous geographic distribution. We first quantify the resolution of our method according to both data and parametrization characteristics. It appears that for reasonable density contrast values (0.1 g cm−3) crustal structures have to be wider than ∼28 km to be detectable in the GOCE signal. Deeper bodies are distinguishable for greater size (35 km size at 50 km depth, ∼80 km at 300 km depth). We invert the six tensor components, among which five are independent. By carefully testing each of them and their different combinations, we enlighten a trade off between the recovery of data and the sensitivity to inversion parameters. We particularly discussed this characteristic in terms of geometry of the synthetic model tested (structures orientation, 3-D geometry, etc.). In terms of RMS value, each component is always better explained if inverted solely, but the result is strongly affected by the inversion parametrization (smoothing, variances, etc.). On the contrary, the simultaneous inversion of several components displays a significant improvement for the global tensor recovery, more dependent on data than on density variance or on smoothness control. Comparing gravity and gradient inversions, we highlight the superiority of the GG data to better reproduce the structures especially in terms of vertical location. We successfully test our method on a realistic case of a complex subduction case for both gradient and gravity data. While the imaging of small crustal structures requires terrestrial gravity data set, the longest wavelength of the slab is well recovered with both data sets. The precision and homogeneous coverage of GOCE data however, counterbalance the heterogeneous and often quite non-existence coverage of terrestrial gravity data. This is particularly true in large areas which requires a coherent assemblage of heterogeneous data sets, or in high relief, vegetally covered and offshore zones. Numéro de notice : A2020-823 Affiliation des auteurs : UMR IPGP-Géod+Ext (2020- ) Autre URL associée : vers HAL Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1093/gji/ggaa318 Date de publication en ligne : 26/06/2020 En ligne : https://doi.org/10.1093/gji/ggaa318 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=97260 [article]

The 2018–2019 seismo-volcanic crisis east of Mayotte, Comoros islands: seismicity and ground deformation markers of an exceptional submarine eruption / Anne Lemoine in Geophysical journal international, vol 223 n° 1 (October 2020)  

Public [article]  inGeophysical journal international > vol 223 n° 1 (October 2020) . - pp 22 - 44 Titre : The 2018–2019 seismo-volcanic crisis east of Mayotte, Comoros islands: seismicity and ground deformation markers of an exceptional submarine eruption Type de document : Article/Communication Auteurs : Anne Lemoine, Auteur ; Pierre Briole, Auteur ; Didier Bertil, Auteur ; Agathe Roullé, Auteur ; Michael Foumelis, Auteur ; Isabelle Thinon, Auteur ; Daniel Raucoules, Auteur ; Marcello de Michele, Auteur ; Pierre Valty , Auteur ; Roser Hoste Colomer, Auteur Année de publication : 2020 Article en page(s) : pp 22 - 44 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] Comores (îles) [Termes IGN] coordonnées GPS [Termes IGN] éruption volcanique [Termes IGN] fond marin [Termes IGN] interféromètrie par radar à antenne synthétique [Termes IGN] Mayotte [Termes IGN] séisme Résumé : (auteur) On 10 May 2018, an unprecedented long and intense seismic crisis started offshore, east of Mayotte, the easternmost of the Comoros volcanic islands. The population felt hundreds of events. Over the course of 1 yr, 32 earthquakes with magnitude greater than 5 occurred, including the largest event ever recorded in the Comoros (Mw = 5.9 on 15 May 2018). Earthquakes are clustered in space and time. Unusual intense long lasting monochromatic very long period events were also registered. From early July 2018, Global Navigation Satellite System (GNSS) stations and Interferometric Synthetic Aperture Radar (InSAR) registered a large drift, testimony of a large offshore deflation. We describe the onset and the evolution of a large magmatic event thanks to the analysis of the seismicity from the initiation of the crisis through its first year, compared to the ground deformation observation (GNSS and InSAR) and modelling. We discriminate and characterize the initial fracturing phase, the phase of magma intrusion and dyke propagation from depth to the subsurface, and the eruptive phase that starts on 3 July 2018, around 50 d after the first seismic events. The eruption is not terminated 2 yr after its initiation, with the persistence of an unusual seismicity, whose pattern has been similar since summer 2018, including episodic very low frequency events presenting a harmonic oscillation with a period of ∼16 s. From July 2018, the whole Mayotte Island drifted eastward and downward at a slightly increasing rate until reaching a peak in late 2018. At the apex, the mean deformation rate was 224 mm yr−1 eastward and 186 mm yr−1 downward. During 2019, the deformation smoothly decreased and in January 2020, it was less than 20 per cent of its peak value. A deflation model of a magma reservoir buried in a homogenous half space fits well the data. The modelled reservoir is located 45 ± 5 km east of Mayotte, at a depth of 28 ± 3 km and the inferred magma extraction at the apex was ∼94 m3 s−1. The introduction of a small secondary source located beneath Mayotte Island at the same depth as the main one improves the fit by 20 per cent. While the rate of the main source drops by a factor of 5 during 2019, the rate of the secondary source remains stable. This might be a clue of the occurrence of relaxation at depth that may continue for some time after the end of the eruption. According to our model, the total volume extracted from the deep reservoir was ∼2.65 km3 in January 2020. This is the largest offshore volcanic event ever quantitatively documented. This seismo-volcanic crisis is consistent with the trans-tensional regime along Comoros archipelago. Numéro de notice : A2020-842 Affiliation des auteurs : IGN+Ext (2020- ) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1093/gji/ggaa273 Date de publication en ligne : 03/06/2020 En ligne : https://doi.org/10.1093/gji/ggaa273 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=98513 [article]