The Contribution of Space-Geodetic Techniques to the Understanding of the Present-Day Geodynamics of the Azores Triple Junction

Abstract

Since the last few decades, Space-Geodetic techniques have provided new observations and understanding of many geodynamics processes. They offer an accuracy in position and spatial coverage that was not available using classical meth odologies. Even in regions like the Azores Triple Junction, where the tectonic plates of North America, Eurasia and Nubia meet and that is mostly covered by the ocean, the use of Global Navigation Satellite Systems (GNSS) and Interferometry Synthetic Aperture Radar (InSAR) has undoubtfully contributed to a better understanding of the tectonic and volcanic processes. This chapter focuses on the major contributions obtained with Space-Geodesy in the Azores through a review of results published by different authors that have been actively working in this region since the late eighties. In fact, the first efforts to accurately measure relative crustal deformations between the different islands of the Azores Archipelago date back to 1988, when a network of nine markers (one per island) was observed using the Global Positioning System (GPS). Since then, several networks of GNSS points have been installed and regularly reoccupied in the islands by different research groups, in particular in the Central Group (Graciosa, Terceira, Sao Jorge, Pico, and Faial) and Sao Miguel, where the geodynamic processes of this triple junction manifest themselves through recurrent episodes of seismic and volcanic activity. Additionally, and starting in 1999 (Ponta Delgada), continuously operating GNSS (cGNSS) stations have been installed in almost all islands which permits today permanent monitoring even if the existing coverage is still not optimal. The initial results provided by GNSS studies focused on the understanding of the large-scale processes taking place in Azores by modelling inter-island displacements constrained by estimated angular velocities of the three tectonic plates. More recently, using the denser networks installed, several works have been concentrated on intra-island deformations due to tectonic but also volcanic activity. We also discuss recent results published using InSAR data. This technique has been successful applied worldwide for volcanic studies and Azores is no exception. Several works have been published providing relevant information for the understanding of the tectonic dynamics that are taking place at the different islands of the Archipelago.