QUASI STATIC GRAVITY SIGNATURES IN SLOW TECTONIC ZONES: ASSIMILATION OF NOVEL AEROSPACE DATA AND GEOPHYSICAL MODELING

The main aim of my Ph.D. research project was to investigate the gravitational signatures of the mechanisms that regulate slow rate tectonic deformation in areas where the earthquakes enucleate. 2D thermo-mechanical numerical models are used to simulate the crust-mantle dynamics; in particular, complexities such as compositional stratification of crust-lithosphere system, mantle hydration, phase changes and degree of plate coupling are investigated, exploring how they affect the gravity field and its rate of change in different tectonic environments. A strongly integration between modelling, gravitational and GNSS (Global Navigation Satellite System) data has provided valuable constraints to the analysis. In fact, this work is part of the GravSeis-Gravitational Seismology project, an ESA-founded research project whose objective is to establish a theoretical framework for the detection and characterization of earthquake precursors based on the observations of the gravitational field made by satellite. Gravitational Seismology concept expresses the idea that earthquakes are not generated only by surface displacements but are closely connected to deep masses redistribution involved in the subduction systems. This rearrangement generates density anomalies, which in turn are responsible for the Earth's gravity field anomalies. A first study has been conducted on the Sumatra and Mariana complexes, representative of the two major types of subduction: ocean–continent and ocean–ocean, respectively. In a first phase, a set of numerical tests has been developed, varying three main parameters: prescribed subduction velocity, prescribed subduction dip angle and degree of plate coupling, exploiting how their variation affect the gravity pattern. In a second phase, the study of the EIGEN-6C4 gravitational disturbance patterns of the Sumatra and Mariana subductions has been carried out, allowing to strengthen the analysis of the gravitational signature in ocean–continent and ocean–ocean subductions in terms of the physics of the processes occurring during the convergence of the plates. Model predictions show a good agreement with gravity data, both in terms of wavelengths and magnitude of the gravity anomalies measured in the surroundings of the Sumatra and Marina subductions, supporting that the differences in the style of the gravity anomaly observed in the two areas are attributable to the different environments – ocean-ocean or ocean-continental subduction – that drives a significantly different dynamic in the wedge area. A second study has been carried out developing 2D finite-element thermo-mechanical models, in which the formation of oceanic crust and serpentinite due to the hydration of upwelling mantle peridotite is implemented, to simulate the evolution of the Gulf of Aden from the rift initiation to the development of an active oceanic spreading center. The thermo-mechanical analysis support the hypothesis that the Gulf of Aden developed as a slow passive rift in thin lithosphere with thick crust and that the variations in features along the passive margins could be related to lateral variations in the amount of H2O in the mantle, which determines the different times of mantle melting.