Monitoring lithospheric motions by Satellite geodesy
Abstract: Understanding of global and local Earth’s dynamic processes is of great importance to the Earth’s system knowledge, human life, and sustainability goals (e.g. climatic change and geo-hazard assessment, etc.). The processes are largely affected by the Earth's mass distribution and redistribution, which can be quantified and modelled using simultaneous and complementary data from various geoscience and environmental near earth-orbiting artificial satellites. In this thesis, which is based on five peer-reviewed papers, we study the lithospheric motion and the Earth’s mass change in terms of gravity variation, using a combination of geodetic satellite data and non-geodetic observations. The first paper is concerned with using of gravimetric approach to model sub-crustal horizontal stresses in the Earth’s mantle and their temporal changes using the Gravity Recovery and Climate Experiment (GRACE) data, caused by geodynamical processes such as mantle convection, in Fennoscandia region. We show that the determined horizontal stresses obtained by a gravimetric method are consistent with tectonics and seismic activities. In addition, the secular rate of change of the horizontal stress, which is within 95 kPa/year, is larger outside the uplift dome than inside in the study area. In the second paper, permafrost thawing and its associated gravity change, in terms of groundwater storage (GWS) anomalies changes is studied using the GRACE data and other satellites (e.g. AIRS) and ground-based observations in the northern high-latitude regions. The results of a preliminary numerical analysis reveal a high correlation between the secular trends of greenhouse gases (CO2), temperature, and the equivalent water thickness in the selected regions. Furthermore, the GRACE-based GWS estimates attributed to the permafrost thawing is increased at the annual rates of 3 to 4 cm/year in selected study areas. The third paper investigates the large-scale GRACE-based GWS changes together with different hydrological models over the major oil reservoirs in Sudan. The outcomes are correlated with the available oil wells production data. Moreover, using the freely available Sentinel-1 data, the ground surface deformation associated with oil and water depletion is studied. Our results show that there is a significant correlation between the GRACE-based GWS anomalies and the extracted oil and water volumes. The trend of GWS anomaly changes due to water and oil depletion varies from -18.5 ± 6.3 to -6.2 ± 1.3 mm/year using the CSR GRACE monthly solutions and the best tested hydrological model in this study. Moreover, our Sentinel-1 Synthetic Aperture Radar (SAR) data analysis using Persistent Scatterer Interferometry (PSI) method shows high rate of subsidence, i.e. -24.5 ± 0.85, -23.8 ± 0.96, -14.2 ± 0.85 and -6 ± 0.88 mm/year, over the selected study area.In the fourth paper, a combined Moho model using seismic and gravity data is determined to investigate the relationship between the isostatic state of the lithosphere and seismic activities in the study area (which includes East Africa, Egypt, Congo and Saudi Arabia). Our results show that isostatic equilibrium and compensation state are closely correlated to the seismicity patterns in the study area. This paper presents a method to determine the crustal thickness and crust-mantle density contrast, and consequently one can detect low-density contrast (about 200 kg/m3) and thin crust (about 30 km) near the triple junction plate tectonics in East Africa (Afar triple junction), which confirms the state of over-compensation in the rift valley areas. Furthermore, the density contrast structure of the crust-mantle shows a large correlation with the earthquake activity, sub-crustal stress and volcanic distribution across East Africa. The fifth and last paper investigates the ground surface deformation of Gävle city in Sweden using Sentinel-1 data and PSI technique, as well as analyzing the historical leveling data. The PSI technique is used to map the location of risk zones, and their ongoing subsidence rate. Our PSI analysis reveals that the centre of Gävle city is relatively stable with minor deformation ranging between -2.0 mm/year and +2.0 mm/year in the vertical and East-West components. Furthermore, the land surface toward the northeast of the city is significantly subsiding with an annual rate of about -6 mm/year. The comparison at sparse locations shows a close agreement between the subsidence rates obtained from precise leveling and PSI results. The regional quaternary deposit distribution was correlated with PSI results, and it shows that the subsidence areas are mostly located in zones where the sub-surface layer is marked by artificial fill materials.
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