I Congreso de Postgrado fcfm: ingeniería, ciencias e innovación

70 Santiago, 10 al 12 de agosto, 2022 THE 2020-2021 BRANSFIELD STRAIN SEISMIC SEQUENCE: SPATIAL AND TEMPORAL RELATIONSHIP WITH ORCA VOLCANO AND TECTONICS IMPLICATIONS Nicolás Vera-Cortés 1,2* , Patricio Toledo¹, Sophie Peyrat¹, Adriana Pérez¹, Jaime Campos 1,2 ¹Programa de Ri sgo ísmico (PRS), Santiago, Chil . ²Departamento de Geofísica, Universidad de Chile, Santiago, Chile. *Email: nicolas.vera.c@ug.uchile.cl RESUMEN On the only convergent boundary of Antarctic Plate margin (2% of total border), Phoenix Plate is subducted under South Shetland Islands block inducing interaction between various plates and microplates in a complex kine- matic-tectonic arrangement. In August 2020, a seismic sequence 8 months long started on the Bransfield Strait with a Mw 6.9 mainshock. Based on previous instrumental coverage, later complemented with an intervention campaign that took place in february 2021, we analyzed the local seismicity during this crisis. The methodology consists in the study of the spatial, temporal and energetic behavior of the seismicity compiled in the ISC catalog, complemented by local and regional location. Further, we present a stress distribution analysis according to fo- cal mechanisms obtained by full wave-form time-domain moment tensor inversion with double couple (DC) and compensated linear vector dipole (CLVD) components. We show 21 precise focal mechanisms 17 of them located a few kilometers northeast (NE) Orca volcano, showing both normal and strike-slip faults. Another 4 focal mechanisms are located along-axis of Bransfield Strait, 3 of them present normal faulting, including the mainshock, and a last one with hybrid normal strike-slip faulting. Seismic spatial distribution shows a first cluster nucleated 25 km northeast of Orca volcano with sub - circular shape, and a second one axially elongated to the ridge from 56° to 55°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 until early May 2021. The second cluster is intercalated, starting on January 23th, 2021 with the Mw 6.9 mainshock, followed by aftershocks ceasing on February 13th, 2021. 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, especially when seismicity returns from the second cluster to the first one is an indicator of causality. The wide range of non DC component in seismic moment tensors is coherent with f luid action all along the rupture process which is expected in a volcanic environment. AGRADECIMIENTOS A todo el equipo del Programa de Riesgo Sísmico (PRS) por el espacio y ambiente colaborativo en que se desarrolla este trabajo. REFERENCIAS [1] Almendros, J., Wilcock, W., Soule, D., Teixidó, T., Vizcaíno, L., ... & Schmahl, L. (2020). BRAVOSEIS: Geophysical investigation of rifting and volcanism in the Bransfield strait, Antarctica. [2] Dreger, D. S. (2003). TDMT_INV: Time domain seismic moment tensor inversion. C I E NC I A S D E L A T I E R R A 03