Coseismic Surface Deformation, Fault Modeling, and Coulomb Stress Changes of the March 2021 Thessaly, Greece, Earthquake Sequence Based on InSAR and GPS Data

Abstract

In March 2021 three strong earthquakes with magnitudes (⁠Mw ⁠) of 6.3, 6.0, and 5.2 occurred in Thessaly plain, Greece, on 3, 4, and 12 March, respectively. The modeling of all the three sources, by inversion of Interferometric Synthetic Aperture Radar and Global Positioning System data, indicates a northeast–southwest‐trending extensional stress field with indications for northeast‐dipping sources. The unmapped fault source of the first mainshock (⁠Mw 6.3) is located approximately 6 km to the southwest of the known Larissa fault (LF). Moreover, the fault that was activated during the second mainshock (⁠Mw 6.0) appears to be located more to the north, bordering the Titarisios river valley to the southwest, whereas the third mainshock (⁠Mw 5.2) appears to be triggered at a fault segment located further to the northwest. The Coulomb stress analysis using the slip distributions of the three aforementioned mainshocks revealed a unilateral triggering of the second and third event toward the northwest, and explained the spatial development of the entire aftershock sequence. Furthermore, among the already known active faults in the broader area, only the LF was brought closer to failure as a result of the imparted stress changes.