Modelling co- and post-seismic displacements revealed by InSAR, and their implications for fault behaviour

The ultimate goal of seismology is to estimate the timing, magnitude and potential spatial extent of future seismic events along pre-existing faults. Based on the rate-state friction law, several theoretical physical earthquake models have been proposed towards this goal. Tectonic loading rate and frictional properties of faults are required in these models. Modern geodetic observations, e.g. GPS and InSAR, have provided unprecedented near-field observations following large earthquakes. In theory, according to the frictional rate and state asperity earthquake model, velocity-weakening regions holding seismic motions on faults should be separated with velocity-strengthening regions within which faults slip only aseismically. However, early afterslip following the 2011 MW 9.1 Tohoku-Oki earthquake revealed from GPS measurements was largely overlaid on the historical rupture zones, which challenged the velocity weakening asperity model. Therefore, the performance of the laboratory based friction law in the natural events needs further investigation, and the factors that may affect the estimates of slip models through geodetic modelling should also be discussed systematically. In this thesis, several moderate-strong events were investigated in order to address this important issue. The best-fit co- and post-seismic slip models following the 2009 MW 6.3 Haixi, Qinghai thrust-slip earthquake determined by InSAR deformation time-series suggest that the maximum afterslip is concentrated in the same area as the coseismic slip model, which is similar to the patterns observed in the 2011 Japan earthquake. In this case, complex geometric asperity may play a vital role in the coseismic nucleation and postseismic faulting. The major early afterslip after the 2011 MW 7.1 Van mainshock, which was revealed by one COSMO-SkyMed postseismic interferogram, is found just above the coseismic slip pattern. In this event, a postseismic modelling that did not allow slip across the coseismic asperity was also tested, suggesting that the slip model without slip in the asperities can explain the postseismic observations as well as the afterslip model without constraints on slip in the asperities. In the 2011 MW 9.1 Tohoku-Oki earthquake, a joint inversion with the GRACE coseismic gravity changes and inland coseismic GPS observations was conducted to re-investigate the coseismic slip model of the mainshock. A comparison of slip models from these different datasets suggests that significant variations of slip models can be observed, particularly the locations of the maximum slips. The joint slip model shows that the maximum slip of ~42 m appears near the seafloor surface close to the Japan Trench. Meanwhile, the accumulative afterslip patterns (slip >2 m) determined in previous studies appear in spatial correlation with the Coulomb stress changes generated using the joint slip model. As a strike-slip faulting event, the 2011 MW 6.8 Yushu earthquake was also investigated through co- and post-seismic modelling with more SAR data than was used in previous study. Best slip models suggest that the major afterslip is concentrated in shallow parts of the faults and between the two major coseismic slip patterns, suggesting that the performance of the rate and state frictional asperity model is appropriate in this event. Other postseismic physical mechanisms, pore-elastic rebound and viscoelastic relaxation have also been examined, which cannot significantly affect the estimate of the shallow afterslip model in this study. It is believed that the shallow afterslip predominantly controlled the postseismic behaviour after the mainshock in this case. In comparison to another 21 earthquakes investigated using geodetic data from other studies, complementary spatial extents between co- and post-seismic slip models can be identified. The 2009 MW 6.3 Qinghai earthquake is an exceptional case, in which the faulting behaviours might be dominated by the fault structure (e.g. fault bending). In conclusion, the major contributions from this thesis include: 1) the friction law gives a first order fit in most of natural events examined in this thesis; 2) geometric asperities may play an important role in faulting during earthquake cycles; 3) significant uncertainties in co- and post-seismic slip models can appreciably bias the estimation of fault frictional properties; 4) new insights derived from each earthquake regarding their fault structures and complex faulting behaviours have been observed in this thesis; and (5) a novel package for geodetic earthquake modelling has been developed, which can handle multiple datasets including InSAR, GPS and land/space based gravity changes

Measuring Coseismic Deformation With Spaceborne Synthetic Aperture Radar: A Review

In the past 25 years, space-borne Synthetic Aperture Radar imagery has become an increasingly available data source for the study of crustal deformation associated with moderate to large earthquakes (M > 4.0). Coseismic surface deformation can be measured with several well-established techniques, the applicability of which depends on the ground displacement pattern, on several radar parameters, and on the surface properties at the time of the radar acquisitions. The state-of-the-art concerning the measurement techniques is reviewed, and their application to over 100 case-studies since the launch of the Sentinel-1a satellite is discussed, including the performance of the different methods and the data processing aspects, which still constitute topics of ongoing research

Sensitivity of synthetic aperture laser optical feedback imaging

In this paper we compare the sensitivity of two imaging configurations both based on Laser Optical Feedback Imaging (LOFI). The first one is direct imaging, which uses conventional optical focalisation on target and the second one is made by Synthetic Aperture (SA) Laser, which uses numerical focalisation. We show that SA configuration allows to obtain good resolutions with high working distance and that the drawback of SA imagery is that it has a worse photometric balance in comparison to conventional microscope. This drawback is partially compensated by the important sensitivity of LOFI. Another interest of SA relies on the capacity of getting a 3D information in a single x-y scan

Development, deformation style, and seismic hazard of large normal faults

Young rifts such as the Malawi Rift System, located at the southern end of the East African Rift System, are a natural laboratory for how continents begin to break apart. Extension is typically accommodated by earthquakes within the upper crust. However, where extension occurs at a slow rate, the small number of historically recorded earthquakes likely provides an incomplete view of the potential magnitude range of events, limiting seismic hazard knowledge and the understanding of rift dynamics. Geological and geomorphological studies of faults scarps may help understand how faults develop, structurally evolve and accommodate displacement. Thus, in this thesis, using field and satellite observations of fault scarps, alongside numerical models, I develop a number of new methodologies in order to better understand young rift evolution. I show that the coseismic stress change between two active parallel faults influences whether the faults link, and the linkage style is determined by the distance between the faults. I also show that the orientation of a major border fault in a young rift can be influenced by local stresses and/or weakness at depth, forming faults oblique to what is expected by the regional stress field. Lastly, I identify segmentation on several Malawi Rift System faults from variations in scarp height and steps in the fault traces, and show that the morphology of each can be used to infer the number of prehistoric earthquake events. My work may suggest that large, normal faults in young rifts develop through a specific growth model, and that they can host earthquakes larger in magnitude than historically recorded. This research can help better understand rift evolution and earthquake hazard in the Malawi Rift System, as well as other regions where normal faults have the potential to cause large magnitude earthquakes, such as the Rukwa rift, Baikal rift and the Basin and Range Province

Imagerie plénoptique à travers des milieux complexes par synthèse d'ouverture optique

Nous présentons un nouveau type d'imageur plénoptique appelé LOFI (Laser Optical Feedback Imaging). Le grand avantage de cette technique est qu'elle est auto-alignée, car le laser sert à la fois de source et de détecteur de photons. De plus, grâce à un effet d'amplification intra-cavité produit par la dynamique du laser, et grâce à un marquage acoustique des photons réinjectés, ce dispositif possède une sensibilité ultime au photon unique. Cette sensibilité est nécessaire si l'on veut réaliser des images à travers des milieux diffusants. L'autre intérêt présenté par le caractère plénoptique de notre imageur, est qu'il permet d'obtenir simultanément une double information: la position et la direction de propagation des rayons lumineux. Cette propriété offre des possibilités inhabituelles, comme celle de conserver la résolution d'un objectif de microscope bien au-delà de sa distance de travail, ou encore de pouvoir corriger par un post-traitement numérique les aberrations causées par la traversée d'un milieu hétérogène. Le dispositif LOFI plénoptique semble donc idéal pour une imagerie en profondeur à travers des milieux complexes, tels que les milieux biologiques. Les performances très intéressantes de cette imageur sont cependant obtenues au prix d'un filtrage spatial très coûteux en photons et au prix d'une acquisition des images réalisées point par point, donc relativement lente.We present LOFI (Laser Optical Feedback Imaging). The main advantage of this technique is that it is auto-aligned, as the laser plays both the role of an emitter and a receiver of photons. Furthermore, thanks to an intra-cavity amplification effect caused by the laser dynamics and an acoustic tagging of re-injected photons, this setup reaches a shot noise sensitivity (single photon sensitive). This sensitivity is necessary if our aim is to make images through scattering media. The other interest, which comes from the plenoptic property of our setup, is that one have access to a complete information about light rays (position and direction of propagation). This property implies unusual possibilities like keeping a constant resolution beyond microscope objectives working distance or being able to numerically compensate, after acquisition, aberrations caused by the propagation through heterogeneous media. Our setup is thus ideal for deep imaging through complex media (turbid and heterogeneous) like biological ones. These interesting properties are achieved at the price of a spatial filtering degrading photon collection efficiency and of a point by point image acquisition which is slow.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF