## 5 Discussion  
The historical seismicity of the region of Thessaly is related to the North Transform Fault (NTF), approximately 50 km southeast of the double earthquake. Therefore, knowledge regarding a dynamic error in this area is minimal. Thessaly, Central Greece, is a region of active crustal extension but low strain [67]. This was confirmed both empirically and by the study in [68]. Although the Thessaly region has a well-known history of large earthquakes, the studied region showed only weak seismicity over the last 15 years, which the Hellenic Unified Seismological Network covers. A subcrustal presence suggests that the upper crust deformation was probably caused by large-scale tectonics and plate dynamics. On 3-4 March, two similar magnitudes (M\({}_{\rm w}\) = 6.3 and 6.2, respectively) occurred in the broader area of the Thessaly area. A few hours later, two earthquakes with similar magnitudes (M\({}_{\rm w}\) = 5.3 and 5.2, respectively) were observed in the same region. A rich seismic sequence followed these earthquakes. More specifically, in the first month alone, 2062 earthquakes took place. We used the Hellenic Unified Seismological Network (HUSN) (Figure 2) to study the two 2021 earthquakes in the Elassona in Thessaly, Central Greece. We accurately calculated the epicenter of these two events and computed the moment tensor of the mainshock and other more significant magnitude aftershocks. Two datasets were used for inversion: one using regional stations and the other including only stations close to the mainshock's epicenter. These analyses show that the observed inversion indicates the activation of a normal type faulting and shallow depth for both events. The first-motion body-wave polarities provide information only regarding the onset of the rupture, whereas the inversion of surface waveforms includes information regarding the earthquake centroid (point of highest slip release). Especially for more significant earthquakes, these two points do not necessarily coincide spatially. According to the study in [67], resolving moment tensors, especially strike-slip mechanisms, is challenging when the source depth is much shallower than the wavelength considered during inversion. On the contrary, this is not always the case for moderate events due to the extensive period component's poor quality. Analysis of moderate events is crucial for seismogenic volumes, where many such earthquakes occur, allowing the calculation of their source parameters. Thus, the seismotectonic characteristics of the study area can be determined. Knowing the source parameters for moderate earthquakes is very important for seismically active regions, mainly when no significant events occur. In general, it allows analytical studies to reveal a specific area's tectonics and seismogenic characteristics. In the present work, the applied waveform inversion methodology was calculated using data at regional distances, the source parameters for the most decisive events, and 33 moderate earthquakes with magnitudes of M\({}_{\rm w}\) > 4.0. Finally, the results for the moment tensor solutions of the analyzed aftershocks are shown in Appendix A. Almost all aftershocks of the sequence occurred north of the surface rupture. Interestingly, the aftershocks were concentrated along the edges of the presumptive rupture plane. This effect is visible on the map view as a gap of aftershocks north of the central part of the surface rupture. The seismicity gap is visible at the shallow depth of the first mainshock on the east-west depth section. Considering only the aftershocks that occurred in March 2021, they spread in the east-west direction. From the different depths for the first mainshock and the east-west extent of the aftershock distribution, we estimated the size of the rupture plane and recorded and visualized its spreading. Figure 11 represents the relation time versus the event's magnitude in the study area. It was observed that most aftershocks occurred within the first three months in the first 75 days.