São Jorge's Volcano-Tectonic Unrest in 2022: A Joint Interpretation Through GNSS and Fully Automated Seismic Analysis

Abstract

The Azores Triple Junction offers a unique opportunity to investigate the interplay between volcanism and tectonic activity. After 60 years of quiescence in São Jorge Island, in March 2022, the island experienced a volcano-tectonic unrest, accompanied by widely felt earthquakes and surface deformation. We conducted an extensive study of this anomalous activity throughout 2022, through a purely automated analysis based on a deep-learning approach for seismic activity, combined with the processing and analysis of data from GNSS stations in the archipelago. The joint interpretation of ground deformation and seismicity suggests a failed magmatic eruption, which we have summarized in a four-stage conceptual model. The unrest began on 16 March 2022 with a period of vertical uplift that lasted for 2 days. On 19 March, the deformation reversed with a burst of seismicity that marked a rapid dike intrusion in the crust which abruptly stopped a few kilometers under the surface. Over the following weeks, the relocated seismicity suggests an intense overpressure near the Moho discontinuity and reveals, in great detail, a lateral magmatic expansion in a sill-like pattern. Finally, from the second week of April until the end of the year a decrease in seismic activity and a lack of deformation registered, indicates a decline and stabilization of the volcano-tectonic process.