## 3 Results  
Figure 3 synthesizes the mapping of the vertical structure (1D) of the \(\rho_{a}\) along the time, including the \(\rho_{a}\) anomalies (\(\Delta\rho_{a}/\overline{\rho_{a}}\) %), the \(\mathrm{K_{p}}\) index, the depth of the hypocentral solutions of earthquakes with \(\mathrm{m_{b}>4.0}\), and measurements of the emissions of CH\({}_{4}\) and CO\({}_{2}\) in the Marambio Station. The first significant event of the seismic swarm in the Bransfield Strait, south of King George Island, occurred on 2020/8/29, 12:47:3.768 UTC, Lat 62.4437S, Lon 58.1777W, H = 10 km, and \(\mathrm{M_{ww}=4.9}\) (moment W-phase [12]). In terms of real values of \(\rho_{a}\) or anomalies, we detected changes of \(\rho_{a}\) approximately four hours previous to the event. Thirty-one hours later, another event of \(\mathrm{M_{ww}=5.4}\) occurred, approximately 25 km from the last event, preceded by a large \(\rho_{a}\) anomaly, which reached almost the surface (Figure 4). Other minor \(\rho_{a}\) anomalies were also detected in this time window with connection to the deeper 1D-\(\rho_{a}\) structure or related to the solar activity as suggested by the \(\mathrm{K_{p}}\) indexes. The larger \(\rho_{a}\) anomalies (A and B) did not match with large \(\mathrm{K_{p}}\) indexes, meaning that the anomalies were not influenced by solar activity. High values of \(\rho_{a}\) near the surface (upper panel in Figure 3) could be interpreted as the not-well-consolidated permafrost and ice, and the permanent low values of the \(\rho_{a}\) anomalies around 10 km depth could be related to a lithological transition in the local structure of the upper lithosphere near the measurement instrument, which may connect other deeper and shallower fractures that facilitate the fluid migration. Figure 4 shows details after starting the large anomaly (A) appreciated in Figure 3 on 2020/8/30, where it is possible to observe a shallowing of the \(\rho_{a}\) anomalies that match the beginning of more significant emissions of CH\({}_{4}\) and CO\({}_{2}\) in the Marambio Station. It suggests that pore pressure perturbations generated by the tectonic stress field disturbances in the region, meaning those that triggered the earthquakes, e.g., events of 2020/8/29, 12:47:3.768 UTC, and 2020/8/30, 19:42:27.389 UTC, with magnitudes \(\mathrm{M_{ww}=4.9}\) and \(\mathrm{M_{ww}=5.4}\), respectively, could be responsible for the migration of fluids and gases that reached the surface, which may be related to changes in the \(\rho_{a}\) (from deeper sources up to the surface, as suggested by the yellow arrows). Gases detected by the Marambio Station are typically stored in the permafrost near the measurement instrument [13]. Thus, pore pressure perturbations from the seismic source in the Bransfield Basin could promote their trigger emission in Marambio Island. We also observed that there was a sudden increase in CO\({}_{2}\) gas. However, the variation of the CH\({}_{4}\) did not have the same trend. We speculate that contrasting concentrations of these gasses near the measurement instrument may explain this behavior. Figure 4: Time window after starting large anomaly (A) and presented in Figure 3, which shows a shallowing of the \(\rho_{a}\) anomalies (suggested by yellow arrows in the second panel) that coincide with the beginning of more significant emissions of CH\({}_{4}\) and CO\({}_{2}\) in the Marambio Station. These gasses are typically stored in the permafrost near the measurement instrument [13], but regional pore pressure perturbances promote their trigger emission. Deeper and strong anomalies in the 1D–\(\rho_{a}\) structure seem to be influenced by solar activity, as shown the K\({}_{\rm p}\) index distribution. Precipitation data are taken from [[https://power.larc.nasa.gov/data](https://power.larc.nasa.gov/data)]([https://power.larc.nasa.gov/data](https://power.larc.nasa.gov/data))–access–viewer/ (accessed on 15 December 2022). Figure 3: Evolution of the 1D–\(\rho_{a}\) structure.