The Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies is currently designing CanX-4 and CanX-5, a pair of formation-flying nanosatellites that will target centimeter-level position determination and sub-meter control. Once formation flight has been demonstrated, future missions can carry payloads designed to exploit these capabilities. Earth Observation is one such application that can benefit greatly from the availability of multiple platforms with precise position determination and attitude control. This work explores multistatic interferometric synthetic aperture radar (InSAR) as a particularly promising implementation of formation flight. Several mission scenarios are considered, including three commonly proposed InSAR constellation configurations, namely the Cartwheel, the Cross-Track Pendulum, and the Car-Pe configuration, as well as three large ( kilowatt) SAR transmitters (L-, C- and X-band) and one microsatellite transmitter (X-band, 150W). Using a framework of STK and MATLAB simulation and analysis tools, each case is evaluated with respect to the available interferometric baselines, ground coverage, resolution, and utility for selected applications including digital elevation modeling, moving target detection, and superresolution imagery. The “large” X-band transmitter is found to produce the most favorable operating area and resolution, and the Car-Pe configuration provides the greatest utility and flexibility for a combination of the three selected applications.

The Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies is currently designing CanX-4 and CanX-5, a pair of formation-flying nanosatellites that will target centimeter-level position determination and sub-meter control. Once formation flight has been demonstrated, future missions can carry payloads designed to exploit these capabilities. Earth Observation is one such application that can benefit greatly from the availability of multiple platforms with precise position determination and attitude control. This work explores multistatic interferometric synthetic aperture radar (InSAR) as a particularly promising implementation of formation flight. Several mission scenarios are considered, including three commonly proposed InSAR constellation configurations, namely the Cartwheel, the Cross-Track Pendulum, and the Car-Pe configuration, as well as three large ( kilowatt) SAR transmitters (L-, C- and X-band) and one microsatellite transmitter (X-band, 150W). Using a framework of STK and MATLAB simulation and analysis tools, each case is evaluated with respect to the available interferometric baselines, ground coverage, resolution, and utility for selected applications including digital elevation modeling, moving target detection, and superresolution imagery. The “large” X-band transmitter is found to produce the most favorable operating area and resolution, and the Car-Pe configuration provides the greatest utility and flexibility for a combination of the three selected applications.

This work makes an attempt to explain the origin, features and potential applications of the elevation bias of the synthetic aperture radar interferometry (InSAR) datasets over areas covered by vegetation. The rapid development of radar-based remote sensing methods, such as synthetic aperture radar (SAR) and InSAR, has provided an alternative to the photogrammetry and LiDAR for determining the third dimension of topographic surfaces. The InSAR method has proved to be so effective and productive that it allowed, within eleven days of the space shuttle mission, for acquisition of data to develop a three-dimensional model of almost the entire land surface of our planet. This mission is known as the Shuttle Radar Topography Mission (SRTM). Scientists across the geosciences were able to access the great benefits of uniformity, high resolution and the most precise digital elevation model (DEM) of the Earth like never before for their a wide variety of scientific and practical inquiries. Unfortunately, InSAR elevations misrepresent the surface of the Earth in places where there is substantial vegetation cover. This is a systematic error of unknown, yet limited (by the vertical extension of vegetation) magnitude. Up to now, only a limited number of attempts to model this error source have been made. However, none offer a robust remedy, but rather partial or case-based solutions. More work in this area of research is needed as the number of airborne and space-based InSAR elevation models has been steadily increasing over the last few years, despite strong competition from LiDAR and optical methods. From another perspective, however, this elevation bias, termed here as the “biomass impenetrability”, creates a great opportunity to learn about the biomass. This may be achieved due to the fact that the impenetrability can be considered a collective response to a few factors originating in 3D space that encompass the outermost boundaries of vegetation. The biomass, presence in InSAR datasets or simply the biomass impenetrability, is the focus of this research. The report, presented in a sequence of sections, gradually introduces terminology, physical and mathematical fundamentals commonly used in describing the propagation of electromagnetic waves, including the Maxwell equations. The synthetic aperture radar (SAR) and InSAR as active remote sensing methods are summarised. In subsequent steps, the major InSAR data sources and data acquisition systems, past and present, are outlined. Various examples of the InSAR datasets, including the SRTM C- and X-band elevation products and INTERMAP Inc. IFSAR digital terrain/surface models (DTM/DSM), representing diverse test sites in the world are used to demonstrate the presence and/or magnitude of the biomass impenetrability in the context of different types of vegetation – usually forest. Also, results of investigations carried out by selected researchers on the elevation bias in InSAR datasets and their attempts at mathematical modelling are reviewed. In recent years, a few researchers have suggested that the magnitude of the biomass impenetrability is linked to gaps in the vegetation cover. Based on these hints, a mathematical model of the tree and the forest has been developed. Three types of gaps were identified; gaps in the landscape-scale forest areas (Type 1), e.g. forest fire scares and logging areas; a gap between three trees forming a triangle (Type 2), e.g. depending on the shape of tree crowns; and gaps within a tree itself (Type 3). Experiments have demonstrated that Type 1 gaps follow the power-law density distribution function. One of the most useful features of the power-law distributed phenomena is their scale-independent property. This property was also used to model Type 3 gaps (within the tree crown) by assuming that these gaps follow the same distribution as the Type 1 gaps. A hypothesis was formulated regarding the penetration depth of the radar waves within the canopy. It claims that the depth of penetration is simply related to the quantisation level of the radar backscattered signal. A higher level of bits per pixels allows for capturing weaker signals arriving from the lower levels of the tree crown. Assuming certain generic and simplified shapes of tree crowns including cone, paraboloid, sphere and spherical cap, it was possible to model analytically Type 2 gaps. The Monte Carlo simulation method was used to investigate relationships between the impenetrability and various configurations of a modelled forest. One of the most important findings is that impenetrability is largely explainable by the gaps between trees. A much less important role is played by the penetrability into the crown cover. Another important finding is that the impenetrability strongly correlates with the vegetation density. Using this feature, a method for vegetation density mapping called the mean maximum impenetrability (MMI) method is proposed. Unlike the traditional methods of forest inventories, the MMI method allows for a much more realistic inventory of vegetation cover, because it is able to capture an in situ or current situation on the ground, but not for areas that are nominally classified as a “forest-to-be”. The MMI method also allows for the mapping of landscape variation in the forest or vegetation density, which is a novel and exciting feature of the new 3D remote sensing (3DRS) technique. Besides the inventory-type applications, the MMI method can be used as a forest change detection method. For maximum effectiveness of the MMI method, an object-based change detection approach is preferred. A minimum requirement for the MMI method is a time-lapsed reference dataset in the form, for example, of an existing forest map of the area of interest, or a vegetation density map prepared using InSAR datasets. Preliminary tests aimed at finding a degree of correlation between the impenetrability and other types of passive and active remote sensing data sources, including TerraSAR-X, NDVI and PALSAR, proved that the method most sensitive to vegetation density was the Japanese PALSAR - L-band SAR system. Unfortunately, PALSAR backscattered signals become very noisy for impenetrability below 15 m. This means that PALSAR has severe limitations for low loadings of the biomass per unit area. The proposed applications of the InSAR data will remain indispensable wherever cloud cover obscures the sky in a persistent manner, which makes suitable optical data acquisition extremely time-consuming or nearly impossible. A limitation of the MMI method is due to the fact that the impenetrability is calculated using a reference DTM, which must be available beforehand. In many countries around the world, appropriate quality DTMs are still unavailable. A possible solution to this obstacle is to use a DEM that was derived using P-band InSAR elevations or LiDAR. It must be noted, however, that in many cases, two InSAR datasets separated by time of the same area are sufficient for forest change detection or similar applications.

Synthetic aperture radar interferometry (InSAR) is a technique that enables generation of Digital Elevation Models (DEMs) and detection of surface motion at the centimetre level using radar signals transmitted from a satellite or an aeroplane. Deformation observations can be performed due to the fact that surface motion, caused by natural and human activities, generates a local phase shift in the resultant interferogram. The magnitude of surface deformation can be estimated directly as a fraction of the wavelength of the transmitted signal. Moreover, differential InSAR (DInSAR) eliminates the phase signal caused by relief to yield a differential interferogram in which the signature of surface deformation can be seen. Although InSAR applications are well established, the improvement of the interferometry technique and the quality of its products is highly desirable to further enhance its capabilities. The application of InSAR encounters problems due to noise in the interferometric phase measurement, caused by a number of decorrelation factors. In addition, the interferogram contains biases owing to satellite orbit errors and atmospheric heterogeneity These factors dramatically reduce the stlectiveness of radar interferometry in many applications, and, in particular, compromise detection and analysis of small-scale spatial deformations. The research presented in this thesis aim to apply radar interferometry processing to detect small-scale surface deformations, improve the quality of the interferometry products, determine the minimum and maximum detectable deformation gradient and enhance the analysis of the interferometric phase image. The quality of DEM and displacement maps can be improved by various methods at different processing levels. One of the methods is filtering of the interferometric phase. / However, while filtering reduces noise in the interferogram, it does not necessarily enhance or recover the signal. Furthermore, the impact of the filter can significantly change the structure of the interferogram. A new adaptive radar interferogram filter has been developed and is presented herein. The filter is based on a modification to the Goldstein radar interferogram filter making the filter parameter dependent on coherence so that incoherent areas are filtered more than coherent areas. This modification minimises the loss of signal while still reducing the level of noise. A methodology leading to the creation of a functional model for determining minimum and maximum detectable deformation gradient, in terms of the coherence value, has been developed. The sets of representative deformation models have been simulated and the associated phase from these models has been introduced to real SAR data acquired by ERS-1/2 satellites. A number of cases of surface motion with varying magnitudes and spatial extent have been simulated. In each case, the resultant surface deformation has been compared with the 'true' surface deformation as defined by the deformation model. Based on those observations, the functional model has been developed. Finally, the extended analysis of the interferometric phase image using a wavelet approach is presented. The ability of a continuous wavelet transform to reveal the content of the wrapped phase interferogram, such as (i) discontinuities, (ii) extent of the deformation signal, and (iii) the magnitude of the deformation signal is examined. The results presented represent a preliminary study revealing the wavelet method as a promising technique for interferometric phase image analysis.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16815号 / 工博第3536号 / 新制||工||1535(附属図書館) / 29490 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 松岡 俊文, 教授 小池 克明, 教授 田村 正行 / 学位規則第4条第1項該当

Cette thèse porte sur l’étude de la déformation de surface (petite et grande déformation) pouvant être détectée en utilisant la méthode de l’interférométrie "InSAR " pour le traitement des images SAR (Synthetic Aperture Radar, bande C : λÉ = 5.6 cm) et signal associé à synthèse d'ouverture. Les nouveaux développements des techniques de traitement InSAR permettent le suivi de la déformation en surface avec une précision de l'ordre millimétrique. Les traitements dites conventionnels de l'InSAR utilisent une paire d'images SAR ("Maitre" et "Esclave") afin de mesurer la différence de phase entre les deux prises de la même scène d'image à des moments différents. Les incertitudes dans les mesures obtenus à partir du traitement conventionnel de l'InSAR sont nombreuses : la décorrelation dans le signal en raison du délai du à l'atmosphère, la contribution topographique et les positions orbitales sont les handicaps majeurs de cette technique. En 2001, Ferretti et al. ont introduit une nouvelle méthode appelée Permanent Scatterer (PS-InSAR) également connue sous le nom de Persistent Scatterer. Pour cette méthode, nous utilisons une série d'images, dont une dite esclave pour construire des interférogrammes avec la même image dite « Maître ». Cette méthode permet d'améliorer le signal de visé (LOS) en terme de correlation pour chaque pixel (PS) en utilisant les meilleurs réflecteurs donnant une corrélation maximale (à partir de l'amplitude et/ou la phase) dans le temps et dans l'espace. Un grand nombre d'algorithmes a été élaboré à cet effet en utilisant le même principe (des variantes) décrit auparavant. En 2002, Berardino et al. publient un nouveau algorithme développé pour le suivi de la déformation en surface en se basant sur les interférogrammes produits à partir des couples d’image SAR ayant une petite séparation spatial (SBAS) de la ligne de base.Dans cette thèse, les techniques InSAR sont appliquées pour différents cas d’étude allant de la petite déformation en surface telle que: 1) Un affaissement dans une zone de puits de pétrole, 2) des glissements de terrain dans une zone urbaine, et 3) la déformation lente à travers les zones de failles des zones sismiques. Afin d'étudier la petite déformation j'opte pour l’utilisation des deux algorithmes (PS et SBAS) dit de traitement multi-temporelle de l’InSAR incorporés dans le logiciel StaMPS (Hooper, 2008). Ainsi, j’ai pu calculer la méthode de combinaison ou hybride entre PS et SBAS et ce, pour toutes les études de cas présentées dans cette thèse. Par ailleurs, certains logiciels en libre accès sont utilisés tout au long de cette thèse tel que, Roi-pac (Rosen et al., 2004) pour aligner les images SAR ainsi que Doris (Kampes et al., 2003) pour calculer interférogrammes à partir de images SAR.[...] / This thesis aims at the study of small to large surface deformation that can be detected using the remote sensing interferometric synthetic aperture radar (InSAR) methods. The new developments of InSAR processing techniques allow the monitoring of surface deformation with millimeter surface change accuracy. Conventional InSAR use a pair of SAR images (“Master” and “Slave” images) in order to measure the phase difference between the two images taken at different times. The uncertainties in measurements using the conventional InSAR due to the atmospheric delay, the topographic changes and the orbital artifacts are the handicaps of this method. The idea of InSAR method is to measure the phase difference between tow SAR acquisitions. These measure refere to the ground movment according to the satellite position. In interferogram the red to blue colors refere to the pixel movement to or far from the satellite position in Line-Of-Sight (LOS) direction. In 2000’s, Radar spacecraft have seen a large number of launching mission, SAR quisitions and InSAR applicability have seen explosion in differents geophysical studies due to the important SAR datas and facility of data accessibity. This SAR-mining needs other type and generation of InSAR processing.In 2001, Ferretti and others introduce a new method called Permanent Scatterer InSAR (PS) that is based on the use of more than one Slave image in InSAR processing with the same Master image. This method allows enhancing the LOS signal for each pixel (PS) by using the best time and/or space-correlated signal (from amplitude and/or from phase) for each pixel over the acquisitions. A large number of algorithms were developed for this purpose using thesame principle (variantes). In 2002, Berardino et al developed new algorithm for monitoring surface deformation based on the combination of stack of InSAR results from SAR couples respecting small baseline (SB) distance. Nowadays, these two methods represent the existing time series (TS) analysis of SAR images approaches. In addition, StaMPS software introduced by Hooper and others, in 2008 is able to combine these two methods in order to take advantages from both of this TS approaches in term of best signal correlation and reducing the signal noise errors. In this thesis, the time series studies of surface changes associate to differents geophysical phenomena will have two interest: the first is to highlight the PS and SBAS results and discuss the fiability of obtained InSAR signal with comparation with the previous studies of the same geophysical case or observations in the field and in the second time, the combined method will also validate the results obtained separately with differents TS techniques. The validation of obtained signal is assured by these two steeps: Both of PS and SBAS methods should give relatively the same interferograms and LOSdisplacement signal (in term of sign and values), in addition these results will be compared with the previous studies results or with observations on the field.In this thesis, the InSAR techniques are applied to different case-studies of small surface deformation [...]

This dissertation explores the combination of Interferometric Synthetic Aperture Radar (InSAR) results with field data to provide additional constraints on the processes controlling deformation signals observed at Galeras volcano (Colombia) and Santorini volcano (Greece). InSAR measurements during 2007-2008 at Galeras reveal a subsidence signal on its northeast flank. I model InSAR and gravity data to determine the best-fit parameters for the subsidence source and suggest this signal was caused by deflation of the magma chamber associated with the January 2008 eruption. In January 2011, Santorini volcano entered a period of unrest characterised by earthquake swarms and caldera-wide uplift. I analyse satellite data over a period incorporating both the preceding phase of quiescence (1993-2010) and the phase of unrest (2011-2012). A subsidence signal is confirmed on the intra-caldera island of Nea Kameni during 1993-2010. I investigate several possible scenarios for its source, with my preferred explanation being a combination of cooling and contraction of historic lava flows, and loading from these flows inducing relaxation of the substrate. I also use a joint InSAR/GPS inversion technique to model the caldera-wide uplift observed during 2011-2012. I determine the optimal parameters for the deformation source and the temporal variation in volume change within the shallow magma chamber. The renewed activity offered an opportunity to observe how soil-gas emissions would respond to an influx of magma to a shallow reservoir. I employ a new approach (222Rn-δ¹³C systematics) to identify and quantify the source of diffuse degassing at Santorini during the period of unrest. Finally, I present a new high-resolution merged LiDAR-Bathymetry grid, enabling detailed mapping of both onshore and offshore historic lava flows emplaced in the centre of Santorini caldera. Updated lava volumes provide new extrusion rate estimates and a means of estimating both the size and duration of future dome-building eruptions at Santorini.

The Qadimah Fault has been mapped as a normal fault running through the middle of a planned $$$50 billion city. For this reason, there is an urgent need to evaluate the seismic hazard that the fault poses to the new development. Although several geophysical studies have supported the existence of a fault, the driving mechanism remains unclear. While a fault controlled by gravity gliding of the overburden on a mobile salt layer is unlikely to be of concern to the city, one caused by the continued extension of a normal rotational fault due to Red Sea rifting could result in a major earthquake. A number of geomorphology and geodetic techniques were used to better understand the fault. An analysis of topographic data revealed a sharp discontinuity in slope aspect and hanging wall tilting which strongly supports the existence of a normal fault. A GPS survey of an emergent reef platform which revealed a tilted coral surface also indicates that deformation has occurred in the region. An interferometric synthetic aperture radar investigation has also been performed to establish whether active deformation is occurring on the fault. Ground movements that could be consistent with inter-seismic strain accumulation have been observed, although the analysis is restricted by the limited data available. However, a simple fault model suggests that the deformation is unlikely due to continued crustal stretching. This, in addition to the lack of footwall uplift in the topography data, suggests that the fault is more likely controlled by a shallow salt layer. However, more work will need to be done in the future to confirm these findings.

California has experienced an unusually dry past two decades punctuated by three intense multi-year droughts from 2007-2010, 2012-2015, and 2020-2022. A portion of the water lost during these two decades is due to intense groundwater overdraft of the Central Valley Aquifer. This groundwater overdraft has led to poroelastic compaction of the aquifer system and subsidence of the land surface. Water mass loss also causes elastic deformation of the solid Earth, an opposite and smaller amplitude response than the poroelastic deformation of aquifer systems. These mass changes can disturb the regional stress field, which may influence earthquake activity. Both the elastic and poroelastic deformation responses can be observed using satellite-based geodetic tools including Global Navigation Satellite System (GNSS) station displacements and Interferometric Synthetic Aperture Radar (InSAR). In this dissertation, I model aquifer-system compaction at depth using InSAR-based vertical land motion during the 2007-2010 drought and evaluate hazards related to Earth fissures, tensional cracks that form at the edges of subsidence zones. Next, I forward-calculate the predicted elastic deformation response to groundwater mass loss over the same period and calculate crustal stress change to evaluate what, if any, impact this has on seismicity in California. In addition to modeling deformation caused by water storage change, I also introduce a new method to jointly invert elastic vertical displacements at GNSS stations with water storage anomalies from the Gravity Recovery and Climate Experiment (GRACE) to solve for water storage changes from 2003-2016 over California. Finally, I expand on this joint inversion framework to include poroelastic deformation measured using InSAR over the Central Valley aquifer-system to solve for a change in water storage and groundwater storage over water years 2020-2021, the most recent drought period in California. / Doctor of Philosophy / Changes in the hydrologic system can have wide-reaching societal, geopolitical, economic, ecological, and agricultural impacts. Proper water management, particularly in places that have water scarcity concerns due to overuse, water pollution, or recurrent drought conditions, is essential to ensure this resource is available to future generations. Current projections of climate change scenarios point to more intense and frequent extreme hydroclimate events. With accelerating population growth in many urban centers across the world, measuring water storage changes has never been more important to ensure resiliency of our cities, energy sector, and agricultural systems. Furthermore, water storage changes deform the Earth, which may create or alter geophysical hazards such as subsidence, the development of Earth fissures, and seismicity. Today, a multitude of space-based geodetic tools allow us to monitor changes in the Earth system, including changes in terrestrial water content and associated deformation, with higher spatial and temporal resolution than ever before. These datasets have provided an unprecedented understanding of hydroclimatic hazards and have resolved constraints arising from sparse and infrequent in-situ measurements. Here, I use space-based geodetic tools and geophysical models to measure water storage fluctuations, deformation, and evaluate associated hazards in California, a region that has experienced an unprecedented nearly continuous two-decades long drought. In general, I find that 21st century droughts have caused significant water storage loss, especially groundwater storage loss, in California, which has exacerbated some geophysical hazards including land subsidence and Earth fissure hazards.

L’éruption d’avril 2007 du Piton de la Fournaise (Île de la Réunion, Océan Indien) a été marquée par les plus gros volumes de lave émis de ces deux derniers siècles, ainsi que par l’effondrement du cratère sommital (le Dolomieu) sur plus de 300 mètres de haut. Des données d’interférométrie radar (InSAR) montrent que les déplacements associés à cette éruption sont inhabituels pour deux raisons : (1) ils ont affecté l’ensemble de l’enclos Fouqué durant l’éruption, (2) deux motifs de déformation ont persisté plus d’un an après la fin de l’éruption. Le premier résulte d’une subsidence centripète du cône central et le second d’un glissement vers l’est du flanc est du volcan. Une méthode, appelée tomographie de déplacements, a été développée pour modéliser les déplacements, basée sur une discrétisation du sous-sol en sources unitaires, et sur la minimisation de deux fonctions coût. Elle permet de trouver une répartition compacte des variations de volume des sources unitaires permettant de reproduire au mieux les déplacements observés. En parallèle, la procédure NA-MBEM, une méthode de modélisation basée sur la combinaison d’un modèle numérique (MBEM) et d’une inversion de type Monte Carlo (NA), a été modifiée pour diminuer le temps de calcul nécessaire à l’obtention d’un bon modèle, et nous montrons que l’utilisation de données temporellement interpolées permet d’améliorer les résultats d’inversion. L’application des deux méthodes de modélisation aux données de déplacements de l’éruption d’avril 2007, montre que durant la période post-éruptive, la subsidence du cône central est provoquée par une source localisée de manière superficielle sous le cône central. Cette source est interprétée comme un système hydrothermal en déflation, dont le drainage aurait été amorcé par l’effondrement du Dolomieu. Les déplacements du flanc est seraient dus à deux sources différentes, toutes les deux superficielles et parallèles à la topographie. L’une est interprétée comme un réservoir temporaire en cours de vidange durant la fin de l’ éruption, et l’autre comme un niveau de glissement sur lequel glisserait le flanc est. Enfin, nous proposons un modèle préliminaire des déplacements ayant eu lieu durant l’éruption, ainsi qu’un scénario de la succession de tous les événements à l’origine des déformations enregistrées entre le 30 mars 2007 et juin 2008. / The April 2007 eruption of Piton de la Fournaise (Réunion Island, Indian Ocean) was characterised by the largest lava emission in the past two centuries, and by a 300 m deep caldera collapse at the summit craters (the Dolomieu). Synthetic aperture radar interferometry (InSAR) data show complex displacements associated with this eruption, which are unusual for two reasons : (i) the whole Enclos Fouqué was affected during the eruption, (ii) two deformation patterns persist more than one year after the end of the eruption. The first signal results from subsidence of the summit area, and the second from a sliding of the volcano’s eastern flank towards the East. A method, called displacement tomography, was developed to model these displacements. It is based on discretization of the volcano’s interior into unitary sources, and on a minimisation of two cost functions to find a compact repartition of the volumetric variations of these sources, which best reproduce the observed displacements. On the other hand, the NA-MBEM procedure (a modelling procedure based on a combination of a fully 3D boundary element method and a Monte Carlo inversion procedure), was improved to reduce the necessary computational time to obtain satisfying results. Furthermore, we show that temporal interpolation of the data improves the inversion results. The application of both modelling methods on the April 2007 displacement data, shows that during the post-eruptive period, the subsidence of the central cone is caused by a shallow source, located under the cone. This source is interpreted as a deflating hydrothermal system, whose drainage could have begun during the Dolomieu collapse. The eastern flank displacements could be the consequence of two sources, both shallow and parallel to the topography. The first one is interpreted as a temporary magma chamber, which is emptying during the end of the eruption. The second one is interpreted as a layer on which the eastern flank was sliding. Finally, we propose a preliminary model of the displacements that occurred during the eruption, and a scenario of the successive events causing the displacements recorded between March 30, 2007, and June 2008.