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Le Piton De La Fournaise (Réunion) Et Le Llaima (Chili) Yu Chen

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Le Piton De La Fournaise (Réunion) Et Le Llaima (Chili) Yu Chen Analyse InSAR des déformations de volcans actifs: le Piton de la Fournaise (Réunion) et le Llaima (Chili) Yu Chen To cite this version: Yu Chen. Analyse InSAR des déformations de volcans actifs: le Piton de la Fournaise (Réunion) et le Llaima (Chili). Volcanologie. Université Toulouse 3 Paul Sabatier (UT3 Paul Sabatier), 2017. Français. tel-01501284 HAL Id: tel-01501284 https://tel.archives-ouvertes.fr/tel-01501284 Submitted on 4 Apr 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. ˲·ª»®­·¬7 ̱«´±«­» í п«´ Í¿¾¿¬·»® øËÌí п«´ Í¿¾¿¬·»®÷ Ç« ÝØÛÒ ´» ¶»«¼· ïê ³¿®­ îðïé ß²¿´§­» ײÍßÎ ¼»­ ¼7º±®³¿¬·±²­ ¼» ª±´½¿²­ ¿½¬·º­æ ´» 笱² ¼» ´¿ Ú±«®²¿·­» øÎ7«²·±²÷ »¬ ´» Ô´¿·³¿ øݸ·´·÷ »¬ ¼·­½·°´·²» ±« ­°7½·¿´·¬7 ÛÜ ÍÜËîÛ æ ͽ·»²½»­ ¼» ´¿ Ì»®®» »¬ ¼»­ д¿²8¬»­ ͱ´·¼»­ Ù7±­½·»²½» Û²ª·®±²²»³»²¬ ̱«´±«­» øËÓÎ ëëêí÷ Ö±­7 ÜßÎÎÑÆÛÍ Ü±³·²·¯«» ÎÛÓÇ Ö«®§ æ אַ·½µ ÞßÝØÛÔÛÎÇ Ð®±º»­­»«® ÔÓÊô Ý´»®³±²¬óÚ»®®¿²¼ ο°°±®¬»«® Ó§®·¿³ ÍÝØÓËÌÆ Ð®±º»­­»«® Ûßô л­­¿½ Û¨¿³·²¿¬»«® Ó·½¸»´ ÎßÞ×ÒÑÉ×ÝÆ Ð®±º»­­»«® ËÐÍô ̱«´±«­» Û¨¿³·²¿¬»«® ͧ´ª¿·² ÞÑÒÊßÔÑÌ ÜÎ ×ÎÜóÙÛÌô ̱«´±«­» Û¨¿³·²¿¬»«® Ö±­7 ÜßÎÎÑÆÛÍ ÓÝ ËÐÍô ̱«´±«­» ײª·¬7ô ¼·®»½¬»«® ¼» ¬¸8­» ܱ³·²·¯«» ÎÛÓÇ ×Î ×ÎÜóÙÛÌô ̱«´±«­» ײª·¬7ô ½±ó¼·®»½¬»«® ¼» ¬¸8­» ABSTRACT We address in this dissertation the use of Interferometric Synthetic Aperture Radar (InSAR) to measure and characterize the ground surface deformation at two volcanoes – Piton de la Fournaise (La Réunion Island, France) and Llaima (Chile). For Piton de la Fournaise, we analyzed the spatial pattern and temporal evolution of the ground displacement between the historical March-April 2007 eruption and October 2014, based on continuous measurements recorded by GNSS stations and X band COSMO-SkyMed and TerraSAR-X/TanDEM-X time series analysis. For the processing of radar data, we adopted a classical InSAR time series approach that exploits the information redundancy in the interferograms and we implemented an original method for correcting artifacts based on the principal component decomposition. The spatial and temporal complexity of the obtained deformation field indicates that an important part of the volcanic edifice is affected by deformations of various origins that overlap spatially and temporally. We observe also subsidence processes that are not accompanied by horizontal displacements in recent lava fields. We show that there exists a linear relationship between the subsidence and the thickness of lava and that the amplitude of subsidence decreases with time. These relationships allow us to construct an empirical law to estimate the contribution of post-lava emplacement process in the deformation field. We also observe that the Central Cone subsides persistently during the study period. We interpret this subsidence as the expression of a relaxation of the stresses caused by the Dolomieu collapse during the March-April 2007 eruption. Finally, we show that a widespread time-dependent moving sector on the Eastern Flank is affected by downslope motion during the 2007-2014 period. The uncertainties on both the structure and rheology parameters of the edifice leads us to explore different hypotheses to explain the origin of this flank motion which could be controlled by the frictional properties of the rocks along one or more fault planes, or be the expression of a dependent ductile deformation of the viscosity of the medium. Llaima is a large Andean stratospheric volcano whose deformation processes are poorly understood not only because of the complexity of its functioning mode but also because of the absence of observation networks on the ground. In this context, the potential of radar data for monitoring the ground deformations of these volcanoes is a main scientific interest. However, 1 the complex environment conditions (steep slopes, snow- or ice-capped summit, dense vegetation cover, and strong tropospheric artifacts) and limited amount of available radar data make it challenging to accurately measure ground displacement with InSAR. To overcome these difficulties, we first perform a detailed analysis of the water vapor variations using Medium- Resolution Imaging Spectrometer (MERIS) and Moderate Resolution Imaging Spectroradiometer (MODIS) near-infrared water vapor products to study the impact of these variations on radar measurements. By using the results of this analysis as a constraint, we implemented an inversion of the radar data acquired between 2003 and 2011 to determine the atmospheric contribution and volume variations of a magmatic source located at a 7 km depth, which allows us to explain the interferometric signals observed during the study period. The results of this inversion show that no deformation caused by a pressure change of this source is detected during the eruptive period of 2008, contrary to what was stated in a previous study. On the other hand, it is possible that an uplift of the edifice preceded the March 2009 eruption. But the variation in volume of the estimated magma chamber (12 × 106 m3) is less than the margin of error determined by least square adjustment. Key words: InSAR; Volcano deformation; Piton de la Fournaise; Llaima; InSAR time series; InSAR artifact correction; Tropospheric phase delay; Lava flow subsidence; Volcano flank motion 2 RESUME Les études des déformations de surface en relation avec l'activité volcanique permettent de quantifier les phénomènes de transfert de magma qui s'opèrent dans les structures superficielles et profondes d'un édifice volcanique. Ces études s'appuient essentiellement sur l'utilisation de séries temporelles acquises par des réseaux de récepteurs GNSS installés sur les flancs de l'édifice volcanique et sur l'utilisation d'images acquises par des satellites équipés de capteurs à ouverture de synthèse. Les objectifs de ce travail ont été de mettre en œuvre sur deux des volcans les plus actifs du monde des méthodes numériques pour détecter, analyser et interpréter les déformations du sol associées à l'activité. Sur le Piton de la Fournaise, nous avons analysé l'évolution spatiale et temporelle du champ de déplacement entre l'éruption historique d'avril 2007 et octobre 2014 à partir de l'analyse de mesures continues acquises par les stations GNSS et de longues séries temporelles d'images radar Cosmos-Skymed et TerraSAR acquises en bande X. Pour le traitement des données radars, nous avons adopté une approche classique qui exploite la redondance d'information dans les interférogrammes et nous avons mis en œuvre une méthode originale de correction des effets troposphériques reposant sur la décomposition des signaux radars en valeurs singulières. La complexité spatiale et temporelle du champ de déplacement obtenu indique qu'une partie importante de l'édifice volcanique est affectée par des déformations d'origines diverses qui se superposent spatialement et temporellement. Ainsi, on observe des processus de subsidence qui ne s'accompagnent pas de déplacements horizontaux sur les coulées de lave récentes. Nous montrons qu’il existe une relation linéaire entre cette subsidence et l'épaisseur de la coulée et que son amplitude décroit avec le temps. Ces relations nous permettent de construire une loi empirique pour estimer la contribution de ce processus dans le champ de déformation. Nous observons également que le cône central subside de manière persistante durant la période étudiée. Nous interprétons cette subsidence comme l'expression d'une relaxation des contraintes provoquée par l'effondrement de plus de 350 m du Dolomieu survenu lors de l'éruption d'avril 2007. Enfin, nous montrons qu'une large partie du flanc est de l'édifice volcanique est affectée d'un mouvement lent le long de la pente entre 2007 et 2014. L' absence d'évidences sur la structure et sur la rhéologie de l'édifice nous amène à explorer différentes hypothèses pour expliquer l'origine de ce glissement qui pourrait être contrôlé par 3 les propriétés frictionnelles des roches le long d'un ou de plusieurs plans de faille, ou bien être l'expression d'une déformation ductile dépendante de la viscosité du milieu. Le Llaima est un large strato-volcans andin dont les processus de déformations sont mal compris à cause principalement de la complexité de son mode de fonctionnement mais, également, aussi par l'absence de réseaux d'observation au sol. Dans ce contexte, les potentialités des données radar pour le suivi des déformations de surface de ces volcans constituent un intérêt scientifique majeur. Néanmoins, le nombre limité d'images radars disponibles, les conditions environnementales spécifiques (relief abrupt, présence de neige, végétation, glacier) et l'impact des effets troposphériques sur les données radars constituent des limites importantes à l'utilisation de cette technique. Dans un premier temps, nous avons réalisé une analyse détaillée des variations de la vapeur d'eau dans la troposphère en utilisant des images MERIS (Medium-Resolution Imaging Spectrometer) et MODIS (Moderate resolution Imaging Spectroradiometer) pour étudier l'impact de ces variations sur les mesures radars. En utilisant comme contrainte les résultats
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