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Analyse de la déformation récente dans le Grand Tunis par interférométrie radar SAR

Abstract : Soil deformation phenomena of natural (tectonic) or anthropic origins (over exploitation of groundwater, embankment) can have adverse effects on the environment and on human life. A good understanding of the mechanism of deformation is essential to mitigate or eliminate risks to infrastructure and natural environments. In this study, it is proposed to apply the interferometric method to study the mobility of an urban and suburban area of Tunis City, which is the main socio-economic center of Tunisia.Seismotectonic analyzes were carried out in the study area to better understand the seismic and structural context of the North East part of Tunisia while being based on the different interpretations made from focal mechanisms and mapping epicentres in this area. This analysis made it possible to deduce the existence of an NW-SE compressive regime that fits well with the existing regime at the regional level. This mapping also allowed the detection of the different zones marked by a relatively large seismic activity with a moderate magnitude and which coincide well with the major accidents that are at the level of the study area. Subsequently, a geomorphological analysis approach of the study area was carried out, which made it possible to highlight the different existing tectonic structures and to distinguish the different morphological units. It has been shown that geomorphological analysis has limitation to interpret the morphodynamic context of the study area and therefore the interferometric technique has proven to be an effective methodology for detecting and monitoring soil displacements with millimeter precision and also improving our understanding of current deformations. Indeed, the application of differential SAR interferometry made it possible to nether identify areas with natural subsidence risks or analyze the deformations of the topographic surface associated with anthropic phenomena. To better assimilate the morphodynamic context of the study area, the interferometric method of Small Baseline Subset (SBAS) developed by Berardino et al. (2002) has been chosen. The analysis of Envisat ASAR (2003-2007, descending satellite orbit) and Sentinel-1B (2016-2018, ascending satellite orbit) SAR data allowed us to obtain soil deformation maps associated with time series of velocity of the study area. These analyzes showed the existence of a differential settlement phenomenon in the region of Tunis and the Mornag plain by quantifying it quite accurately. Therefore, by combining SBAS results with geological, hydrogeological and geotechnical information, we have been able to explore some of the links between soil subsidence and its main control factors, in particular:- a differential settlement detected around the Lake of Tunis region, which is probably due to the nature of highly compressible alluvial sediments with bedrock depths sometimes exceeding 65m;- a subsidence of the Mornag plain, whose overexploitation of groundwater and the compressibility of alluvium were the driving forces of these deformations
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Anis Chaabani. Analyse de la déformation récente dans le Grand Tunis par interférométrie radar SAR. Géotechnique. Université Paris-Est, 2019. Français. ⟨NNT : 2019PESC2002⟩. ⟨tel-02390442⟩

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