Multi-Temporal SAR Interferometry for Monitoring Ground Deformation in Greece.

Abstract

This dissertation is focused on the applications of multi-temporal SAR interferometry techniques to estimate deformation in carefully selected tectonically active areas in the greek territory, never investigated in the past with the use of InSAR time-series analysis. The objective of this dissertation is twofold. The first part of the thesis is focused on the added geophysical knowledge, provided with the employment of PS techniques in deformation mapping. The second part is focused on the improvement of the accuracy of SAR image coregistration, a crucial step during a typical interferometric processing. Amorgos, Kythira islands and the broader area around Polygyros city, were selected fot InSAR time-series analysis. The M w = 6.4 June 1995 Aigion (Gulf of Corinth) earthquake and theM w = 6 September 1999 Athens (Attica) earthquake, served as case studies for the experimental analysis of SAR image coregistarion. Post-seismic deformation on Amorgos island was investigated, for the first time with the use of multi-temporal InSAR techniques. Long time-series analysis was performed on ENVISAT and Sentinel-1 data of more than a decade. The decomposition of LOS velocity vectors to vertical and horizontal motion components, contributed to a more accurate interpretation of the displacement field. The central south coast is experiencing horizontal movement, while uplift of a maximum value of 5mm/y is observed in the southeastern coast. The interpretation of the estimated SAR displacements in Amorgos island, reveals that the observed upper-crust movements may reflect post-event long-term relaxation, which has been recognized to be caused by large earthquakes as redistribution of displacement, strain, and stress. A time-series analysis of more than a decade, from 2003 to 2019 was performed and ground deformation velocity maps, were produced, for Kythira island. The main geodetic deformation pattern dominating a large part of the island is uplift, ranging from 2 to 5 mm/y. We suggest that the current deformation pattern identified in Kythira Island from space geodesy is rather explainable by regional deformation processes rather than by deformation in local small-scale, no active faults on the island. Earthquake-cycle modeling is not helpful in this case, since the historical earthquake record of the area is poorly constrained, while the instrumental seismicity is dominated by the two intermediate-depth earthquakes of 1903 and 2006. Aseismic slip is an alternative mechanism for uplift in plate margins. An additional uplift mechanism that should not be ruled out is sediment underplating. An extensive study over Chalkidiki peninsula and specifically on the broader area of Polygyros city, an area that has been poorly investigated in terms of its tectonic behavior, was conducted, by combining two complementary geodetic observations, GPS and InSAR data. An investigation of hydrogeological studies in the area, reveals an aquifer over-exploitation, due to intense pumping of considerable number irrigation and drinking water boreholes and differences in recharging rate. The PSI results from Sentinel-1 data, are an indication that the water balance in the area might not have been restored after 2014, and that over-exploitation of Moudania watershed continues. An experimental analysis of the coregistration step, using ERS data, was performed and the most efficient combination of algorithms and parameters, evaluated by coherence statistics, is provided. It is worth to be mentioned that all the final selected thresholds and methods, are computationally efficient, compared to more complex methods and the same combination of parameters can be applied as a generalized rule, since it was efficient in areas with diverse terrain types.