A new methodology for detection and interpretation of land uplift using A-DInSAR techniques: London and South Wales Coalfield cases of study

The thesis has been carried out at the University of Pavia and within the Erasmus + Traineeship program in collaboration with the British Geological Survey (BGS). From 1990s the A-DInSAR technology are widely used to study the vertical movement in response to the most varied phenomena for example: landslides (i.e. Wasowski et al., 2014), subsidence caused by mining activity (i.e. Ou et al., 2016) or water withdrawal (i.e. Motagh et al., 2007), volcanic activity (i.e. Di Triglia et al., 2013), earthquakes (i.e. Wrigth et al., 2004) etc. Usually when it comes to vertical movements of the Earth's surface is thought to negative movements, or subsidence, which can manifest for the reasons just described. Conversely, less common and studied are instead the uplift phenomena of the earth surface. Positive movements (uplift) can occur as a result of various causes, for example swelling of clay mineral, fault effect (Amelung et al., 1999), water rebound in mining area (Bateson et al., 2015) etc. often causing environmental problems such as the leakage of mining ground water on the Earth's surface (Johnston et al., 2008). The thesis deals with two cases of uplift both in United Kingdom (the first in the centre of London and the second in the South Wales), both triggered by natural phenomenon and human activity in deeply different geological contexts. Therefore, the purpose of this thesis is to find a common methodology to these two cases, that could be applied for uplift phenomena located in other sites. The method provides: 1) the analysis of the predisposing and triggering factors of uplift phenomena for the study areas. 2) the development of a new methodology to study the uplift phenomena applying the advanced differential interferometric synthetic aperture radar (A-DInSAR). In particular the methodology was developed in three main steps: • (1) A-DInSAR data analysis and validation The categorization of the A-DInSAR data velocities by choosing a stable velocity threshold. Subsequently the validation of the A-DInSAR data using the GNSS stations. • (2) Time series analysis The analysis of the target velocity using the PSTime program (Berti et al., 2013) to individuate a mathematical movement trend of the target. Then the application of Principal Component Analysis (PCA) to detect the spatial-temporal deformation pattern. • (3) Process identification through comparison of A-DInSAR data with predisposing and triggering factors. The analysis of predisposing and triggering factors for each study area with the development of detailed geological sections starting from borehole data and 1:50.000 geological maps. On the geological sections will be reported also the target movements, represented with coloured dots categorised with the LOS velocity. Moreover the anthropic elements (buildings, coal seams), with their characteristics, that influence the target uplift. Then the hydrological analysis to verify how the piezometric surface varies in the time due to the natural and human activity. Moreover the faults and structure analysis to understand how the ground water is influenced by structural elements. Just for the Wales was conducted also a field trip in the areas that today much resent of the past coal mining activity. The methodology that was developed allows, through the steps just described, to study the geological, hydrological and anthropic factors that characterize the uplifting areas. This study has also highlighted the versatility of the A-DInSAR technique which can be used both as a starting point for exploring the geological causes of motion and as a means of interpretation and redefinition of hydrological and structural data.