[Soutenance de thèse] Illuminating fault slip with InSAR: Strain release along the Chaman plate boundary

Résumé : How does a fault accumulate the energy necessary for seismic rupture? Synthetic Aperture Radar Interferometry (InSAR) can measure with a millimetre-precision ground displacements along continental faults between successive passes of satellites at the same location. In this thesis, I identify when and how strain is accommodated across the Chaman plate boundary between India and Eurasia in Pakistan and Afghanistan, a region struck by large earthquakes that remains enigmatic. Nowadays, satellites acquire continuous high-resolution images with the potential to inform us about the evolution of deformation in (almost) real time, a challenge for classic processing techniques. In this thesis, I present a new method for computing InSAR time series, named KFTS, which allows us to iteratively update a pre-existing time series through the appropriate combination of data, models and their respective uncertainties, as satellite images become available. The method is tested on synthetic data as well as interferometric networks on Etna (Italy) and on the Chaman plate boundary. KFTS estimates phase delays and strain rates in agreement with commonly used methods and also computes associated uncertainties. Subsequently, I interpret InSAR time series along the Chaman plate boundary between 2014 and 2020. I find that most of the Chaman fault (CF) slides aseismically and continuously with a loading rate between 0.7 and 1.2 cm/yr and three 80-130 km-long creeping sections. I propose a new segmentation of the CF and discuss the interplay between earthquakes, aseismic slip and fault trace geometry. I image three moderate magnitude earthquakes, which exhibit significant induced aseismic slip. Using InSAR velocities, I map deformation gradients in the fault and fold belt east of the CF. They are interpreted as the surface expression of left-lateral strike-slip on three to four vertical faults. It turns out that most of the current plate boundary deformation focusses to the east of the CF, along the continuation of the Ornach Nal fault to the south and along the Quetta-Kalat fault which is thought to have hosted the 1935 Quetta earthquake of magnitude 7.7. Our description of partitioning is consistent with the geology and suggests an eastward migration of the plate boundary. Jury : Virginie PINEL (Université de Grenoble) : Rapportrice / Roland BÜRGMANN (University of California) : Rapporteur / Jessica C. HAWTHORNE (University of Oxford) : Examinatrice / Laetitia LE POURHIET (Sorbonne Universités) : Examinatrice / Raphaël GRANDIN (IPGP) : Examinateur / Romain JOLIVET (ENS) : Directeur de thèse / Cécile LASSERRE (Université de Lyon) : Invitée Lien Zoom : https://cnrs.zoom.us/j/93798646580?pwd=Ti9vcG00UTB2djNDMDNOWjVSUjVjdz09 Meeting ID: 937 9864 6580 Passcode: 6wjC60