Résumé
Only 2% of Antarctic plate's boundary is convergent, along which Phoenix-plate is subducted under South Shetland Islands block inducing interaction between various plates in a complex kinematic-tectonic arrangement not yet fully understood. In August 2020, a seismic sequence 8 months long started on the Bransfield Strait, reaching a Mw 6.9 mainshock. Based on previous instrumental coverage, later complemented with an intervention campaign that took place in february 2021, we analyzed in spatial, temporal and energetic terms the local seismicity during this crisis and we relate this data to local plate kinematics. Further, we present a stress distribution analysis according to focal mechanisms obtained by full wave-form moment tensor inversion with just double couple (DC) and compensated linear vector dipole (CLVD) components. We show 21 precise focal mechanisms 17 of them located few kilometers northeast of Orca volcano, showing both normal and strike-slip faults. Another 4 focal mechanisms are located along-axis of northern Bransfield Strait, 3 of them present normal faulting, including the mainshock, and a last one with hybrid normal strike-slip faulting. The DC component varies from 9% to 94%, showing both high DC and CLVD component events. Seismic spatial distribution shows two clusters: the first-one nucleated 25 km northeast of Orca volcano with subcircular shape, and the second one axially elongated to the ridge from 56 degrees to 55 degrees W. The first cluster takes place in two stages, the first one takes place between August 29th, 2020 and November 6th, 2020 ending with the Mw 6.0 event without notable aftershocks. This cluster is reactivated on February 14th, 2021 in a diffuse way. The 3 weeks longer second cluster is intercalated, starting on January 23th, 2021 with the Mw 6.9 mainshock, followed by aftershocks. Magnitudes range from 4.5 to 6.9, with powerlaw energy distribution between Mw 5 and 5.5. The closeness between the first cluster and Orca volcano suggest seismic-volcanic interaction, while the second cluster, according to its geometry, is probably related to normal faults on the ridge. Cluster temporalities indicate causality between clusters. The wide range of DC component in seismic moment tensors is coherent with fluid action all along the rupture process which is expected in a volcanic environment.