Preliminary Insights of InSAR Applied to the Earthquake Swarm 2020-2021 in the Granada Basin by Using Open Resources

Earthquakes are one of the more destructive natural hazards when their energy is enough to reach inhabited areas. From the end of 2020 to the beginning of 2021, an earthquake series was registered in the district of La Vega, located in the province of Granada which is characterized by the highest seismicity area in the Iberian Peninsula. This event, defined as an earthquake swarm, with specific characteristics as a non-predictable magnitude of its aftershocks, produced damages in the municipalities close to the epicentres of highest magnitudes. The aftershock with the highest magnitude of 4.4 was recorded on 23 Jan. 2021, with epicentre in the northwest part of the municipality of Santa Fe. Given the importance of this phenomenon, this document focuses on precursory research of its territorial effects in the terms of ground deformation. Thus, the displacement map for three different periods (previous to the earthquake series and co-seismic) is obtained by leveraging the currently available open satellite images of Sentinel-1, processed with the use of open-source tools to assess ground movements of low to very low magnitudes (subcentimetric to centimetric scale). Despite the medium resolution of the Sentinel-1 images and the signal constrains by the atmosphere and decorrelation factors, the distribution and general pattern of displacements was revealed by applying the technique Synthetic Aperture Radar Interferometry. They show the clear distribution of the greatest deformation after the co-seismic interferogram generated for the last period analysed (13 Jan. 2021 – 25 Jan. 2021), which contains the date of the earthquake with the highest magnitude. These highest displacements with a downward direction coincide with the municipalities of Pinos Puente, Atarfe, and Santa Fe, where the majority of damages were documented. Consequently, the potential of the open resources for the assessment of the surface effects related to low and moderate earthquakes in this specific geographical area was demonstrated. Nevertheless, further research can be addressed to obtain more precise measurements or to deepen into the cause-effect and the expected spatial distribution of damages related to different seismic events