Aftershock Patterns of the 2021 Mw 6.3 Northern Thessaly (greece) Earthquake

On March 3, 2021, a strong shallow earthquake of magnitude M-w 6.3 struck Northern Thessaly, an area that lies in one of the most active fault zones of mainland Greece. The mainshock generated numerous aftershocks, with some of large magnitude reaching up to M-w 6.0. In this work, we study the scaling properties and the physical mechanisms of aftershock occurrence during the pronounced aftershock sequence that followed the mainshock. The aftershock sequence obeys well-established scaling relationships, such as the Gutenberg-Richter scaling law for the frequency-magnitude distribution of aftershocks with a b-value of 0.90 +/- 0.03 and a composite model of three modified Omori regimes for the decay of the aftershocks production rate. The distribution of waiting times between the successive aftershocks also presents scaling and a bimodal distribution between two power-law regimes, signifying clustering effects at all time scales in the temporal occurrence of aftershocks. Application of principal component analysis to the spatial distribution of aftershocks indicates that the activated area reached its maximum during the first ten days after the mainshock and then remained constant. Aftershocks mainly propagated along fault strike on a NW-SE direction during the early phase of postseismic relaxation, driven by a combination of co-seismic stress changes and afterslip following the mainshock. Overall, the results presented herein provide important insights into the scaling parameters and the triggering mechanisms of the 2021 Northern Thessaly aftershock sequence, which are essential for better understanding and modeling the aftershock generation process.