The Use of Interferometric Synthetic Aperture Radar for Isolating the Contribution of Major Shocks: The Case of the March 2021 Thessaly, Greece, Seismic Sequence

Abstract

We study the surface deformation following a moderate size M5+ earthquake sequence that occurred close to Tyrnavos village (Thessaly, Greece) in March 2021. We adopt the interferometric synthetic aperture radar (InSAR) technique to exploit several pairs of Sentinel-1 acquisitions and successfully retrieve the ground movement caused by the three major events (M5+) of the sequence. The mainshocks occurred at depths varying from ~7 to ~10 km, and are related to the activation of at least three normal faults characterizing the area previously unknown. Thanks to the 6-day repeat time of the Sentinel-1 mission, InSAR analysis allowed us to detect both the surface displacement due to the individual analyzed earthquakes and the cumulative displacement caused by the entire seismic sequence. Especially in the case of a seismic sequence that occurs over a very short time span, it is quite uncommon to be able to separate the surface effects ascribable to the mainshock and the major aftershocks because the time frequency of radar satellite acquisitions often hamper the temporal separation of such events. In this work, we present the results obtained through the InSAR data analysis, and are able to isolate single seismic events that were part of the sequence.