Integrated Seismic and Geodetic Monitoring of the Recent Seismo- Volcanic Activity on São Jorge Island, Azores (Portugal)

Abstract

On March 19, 2022, at 17:11 UTC IPMA recorded the onset of a seismic swarm character-ized by a high event frequency in the initial hours, reaching up to 700 events per hour, with magnitudes ranging from low to moderate and a maximum magnitude of 4.0 ML. According to the IPMA catalog, the epicenters are distributed along a trend roughly aligned with the island's orientation, forming a strip between Velas and Pico da Esperan-ça, at depths ranging from 7 to 13 km. The onset of seismic swarm's prompted a public alert on São Jorge Island. In the immediate aftermath, the University of Évora (UÉ) , in coordination with IPMA, enhanced the regional seismic monitoring capabilities by in-stalling a series of broadband seismometers and a strong-motion sensor. To strengthen the existing permanent seismic network, several of these instruments were integrated in near-real time through 4G connectivity with both institutions. Interferometric analysis using Sentinel-1 SAR data acquired between March 9 and April 14, 2022, revealed ground deformation ranging from 5.6 to 8.4 cm, extending over a broad area encompass-ing São Jorge, Pico, and Faial islands. In light of these observations, and given the elevat-ed likelihood of a volcanic eruption or a seismic event of greater magnitude than those previously recorded, UÉ and IPMA reinforce the seismic observation by deploying 30 broadband seismographic stations. These new seismic stations were strategically coneed into four compact sub-arrays distributed across São Jorge and Pico islands, aimed at enhancing sensitivity to low-magnitude seismicity. This refined detection capability was fundamental for improving the characterization of earthquake-volcano interactions underlying the detected deformation. In this study, we present an analysis of the seismic activity, associated source mechanisms, and coastal deformation patterns linked to this geodynamic episode.