Complex Coseismic and Postseismic Faulting During the 2021 Northern Thessaly (Greece) Earthquake Sequence Illuminated by InSAR Observations

Abstract

Abstract Three M w > 5.5 earthquakes (Tyrnavos, Elassona and Verdikoussa earthquakes) struck the northern Thessaly, Greece, from 3 March to 12 March 2021, filling a significant seismic gap. We exploit Interferometric synthetic aperture radar data to investigate coseismic deformation of these events and the first half‐year postseismic deformation related to the Tyrnavos event. Our coseismic modeling reveals that the seismic sequence activated at least four unmapped low‐angle normal faults. However, postseismic analysis shows that afterslip propagates updip to a high‐angle shallow structure, indicating that the coseismic slip and afterslip jointly activated a ramp‐flat structure. By a comprehensive analysis of the inversions, fault distribution, relocated aftershocks and regional stress changes, we highlight that intersections between the main and secondary faults control the slip extent and rupture termination in each earthquake and that static stress transfers induced by earlier event encourage the rupture reinitiation of the later event.