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Thèses et Stages

Liste des Sujets proposés par l’équipe ( Master, 1ère et 2ème année )

Retrouvez dans les rubriques à droite les thèses en cours et les thèses soutenues.

Voici ci-dessous une liste de sujets de stages potentiels. N’hésitez pas à nous contacter pour de plus amples informations :

En 2016-2017

- M. Radiguet & L.Audin : Stage de M2R. Coulomb modeling of the stress transfer on inherited crustal faults in the coastal region of a subduction zone : Application to the 2016 Pedernales earthquake

- J. de Sigoyer & P. Sabatier & F. Arnaud : Stage de M2R. Developing archaeoseismicity associated to paleolimnology as a new tool to improve seismic hazard assessment and adaptation of civilisation against seismic risks.

- A. Walsperdorf & A. Socquet & S. Baize : Stage de M2R. Cartographie des taux de déformation géodésiques en France et en Europe.

- A. Socquet & D. Marsan : Stage de M2R. Détection des glissements lents atypiques sur la subduction Japonsaise par combinaison de sismologie et GPS.

- J. Hollingsworth & A. Socquet & C. Lasserre  : Stage de M1. Correlation of historical KH4 optical satellite imagery to measure earthquake and volcanic deformation.

Keywords : remote sensing, image processing, dike injection, earthquake cycle

Summary :
Optical image correlation (OIC) is a modern geodetic technique which measures the relative spatial movement of common features represented by pixels within two or more optical satellite images. Depending on the quality and resolution of the images used in the analysis, pixel shifts as low as 1/10th of the input resolution can be detected. OIC thereby allows for the rapid retrieval of ground deformation over large areas using remotely sensed data. The rich archive of historical optical satellite and aerial photo data available offers the potential for investigating tectonic deformation over the last 60+ years, before GPS or InSAR techniques became available. However, insufficient documentation of the various historical camera systems used, coupled with limited support in modern remote sensing software packages has prevented the widespread use of historical satellite imagery for studying tectonic deformation at the Earth’s surface. In this study, we will investigate the use of KH-4 Corona satellite imagery with the optical image correlation technique. KH4 satellite images were acquired between 1963-1972 using a dual panoramic camera system, and with a ground resolution between 2-3 m. However, no rigorous camera model has currently been developed for the unique imaging geometry of the KH4 system, while the long, narrow film strips make correcting spatial distortions in the images very challenging. In this study, we will make use of a new methodology developed at the University of Arkansas for processing KH4 panoramic satellite images. This processing chain allows for the precise orthrectification of KH4 images using Rational Polynomial Coefficients (RPCs), despite the absence of detailed camera information needed to develop a specific camera model for the KH4 sensor.

We will test this new processing methodology in two locations : (1) East African Rift - we will use KH4 satellite images to measure any surface deformation associated with the 1969 Serdo and 1989 Dobi earthquake sequences. Both earthquakes occurred in Ethiopia, within an extensional rift setting which experiences episodic earthquake and dike injection events. Both earthquakes occurred between two well-known volcanic dike injection events (1978 Asal rift crisis in Djibouti to the east, and the 2005 Dabbahu rift crisis to the west). KH4 imagery will reveal the magnitude and pattern of extensional slip within this little studied transition zone. (2) Eastern Tibet - we will study a sequence of earthquakes which occurred on the Xianshuihe fault, which contributes to the eastward translation of crustal material in Tibet in response to the northward collision of India relative to Asia. Using optical image correlation, we aim to retrieve the co- and post-seismic surface deformation fields for two large earthquakes (1973 Luhuo, and 1981 Daofu) which broke the Xianshuihe fault. Although these events occurred in the recent historical past, their surface offsets were never mapped in the field and remain poorly understood. A better understanding of the surface deformation associated with these events is important to understand the seismic hazard posed by the Xianshuihe fault, and its role in accommodating regional deformation. Furthermore, our fault slip data will be used to investigate the geological and structural factors which influence the expression (and localization) of fault slip at the surface during large earthquakes.

- J. Hollingsworth & MP Doin : Stage de M2R. Noise-reduction in optical image correlation through time-series analysis : application to the 2013 Baluchistan earthquake.

Keywords : remote sensing, inverse modeling, image processing, earthquake cycle

Summary :
Optical image correlation (OIC) is a modern geodetic technique which measures the relative spatial movement of common features represented by pixels within two or more optical satellite images. Depending on the quality and resolution of the images used in the analysis, pixel shifts as low as 1/10th of the input resolution can be detected. OIC thereby allows for the rapid retrieval of ground deformation over large areas using remotely sensed data. Nevertheless, despite increasing volumes of medium resolution (10-15m) satellite data now available, OIC is limited to retrieving deformation signals higher than the background noise level (1/10th pixel, or 1m for 10m resolution imagery). As a result, OIC has so far only been useful in proving information on the spatial pattern of earthquake deformation during the co-seismic phase of rupture, where deformation is large. To study the full seismic cycle (including the smaller post-seismic and inter-seismic phase) a new method is required to reduce the noise level capable with OIC. Until now there has been little discussion of the factors which control the noise content in image correlations. One important source of noise which has not previously been addressed is the influence of sun position on the illumination (cast-shadow content) of a satellite image. During image acquisition, the sun illumination conditions (i.e. sun aspect and elevation) change throughout the year. We expect large differences in the illumination conditions between image pairs to produce shifts of the shadow content, particularly in areas of higher topography, which will influence the correlator and result in large artifacts in the displacement field. In this project, we will first investigate the influence of changing sun illumination by correlating a variety of sun-shaded digital elevation models, thus providing a new way to account for illumination artifacts. We will apply this method to Landsat8 satellite images spanning the 2013 Balouchistan earthquake, which ruptured a 220km-long section of the Hoshab fault in Western Pakistan, slipping up to 12m in a left-lateral sense. The pattern of slip revealed strong segmentation of the fault, which curves along the southern edge of the Hoshab fold. Measurements of near-field displacement, coupled with a rapidly decaying signal away from the fault suggest the majority of slip occurred in the uppermost crust. This contrasts with several previously studied strike-slip earthquakes around the world which show a peak of slip at 3-5km depth, decreasing substantially towards the surface (known as ’Shallow Slip Deficit (SSD)’, see Fialko, et al., 2003). Inversion of optical correlation data to produce a time-series will allow a more acccurate retrieval of the co-seismic phase, thereby allowing a more effective assessment of the degree of SSD for the Balouchistan earthquake. Furthermore, the noise reduction offered by our time-series analysis will allow us to better address the nature of the post-seismic slip phase, which remains poorly characterized due to the lack of InSAR data available at this time. Initial correlation of single image pairs during the post-seismic phase suggest N-S extension may have occurred across the fault. Although such motion is unexpected due to the compressional tectonic setting of this earthquake, it could have occurred in response to dynamic over-shoot in the co-seismic slip phase. We will test this hypothesis by using optical time-series. The speed, magnitude, spatial pattern and localization of post-seismic slip all provide important constraints on the rheological properties of the crust, which are critical for understanding how faults slip in single events and over multiple earthquake cycles. This work will further refine the OIC technique, increasing its effectiveness for studying many processes shaping the Earth’s surface, including volcanic deformation, landlides, glacier flow, and the seismic cycle.

En 2015-2016
- [David Marsan] : SSE à Nankai (subduction japonaise) : analyse conjointe des séries temporelles GPS et des catalogues de sismicité
- [Cécile Lasserre] : Déformation intersismique des failles Guatemaltèques par InSAR
- [Cécile Lasserre] : Interférométrie radar sur les grandes failles chinoises : exploitation des données issues du nouveau satellite Sentinel-1
- [Andrea Walpersdorf & Philippe Vernant (Montpellier)] : Le champ de déformation 3D des Alpes occidentales par 20 ans de données GNSS
- [Virginie Pinel] : Etude du volcan de Colima au Mexique par radar satellitaire (SAR) : Apport des nouvelles données (TerraSAR-X et Sentinel-1)
- [Pascal Lacroix & Marie Pierre Doin] : Séries temporelles de déplacements du glissement de terrain de Maca (Pérou) à partir de corrélation d’images optiques
- [Erwan Pathier & Michel Campillo & Mathilde Radiguet] : SSE au Mexique par InSAR et sismologie
- [Anne Socquet, Nathalie Cotte & Andrea Walpersdorf] : Champ de déformation à l’échelle de l’Europe : Traitement massif de données GNSS dans le cadre du projet d’Observatoire de la plaque Européenne (EPOS-IP)
- [Anne Socquet & Nathalie Cotte] : Variations spatiales et temporelles de la déformation au dessus de la subduction Japonaise : Traitement massif des données du réseau GPS Japonais GEONET

Evolution du délai de phase total (déformation + atmosphère turbulente) autour du lac Siling Co au Tibet sur une fauchée Envisat descendante. On voit la déformation associée à la montée du niveau d’eau dans le lac (au centre), l’effet de la fonte du permafrost au Nord du lac, la déformation post-sismique associée à un petit tremblement de terre au Nord, et à peine discernable, la déformation intersismique associée à la faille de Gyaring Co et au graben au sud du lac (MP. Douin)

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