Neotectonic setting and fault modelling of the nothern Thessaly 2021 earthquake sequence
The Northern Thessaly 2021 earthquake sequence changed the way we see hidden or blind faults. It occurred in Central Greece with three mainshocks of Mw6.3, Mw6.0 and Mw5.6 on 3, 4 and 12 March, respectively. Serious damages were recorded and one indirect death in the villages of the area. The import...
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| Κύριοι συγγραφείς: | , |
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| Άλλοι συγγραφείς: | |
| Γλώσσα: | English |
| Δημοσίευση: |
2023
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| Θέματα: | |
| Διαθέσιμο Online: | http://hdl.handle.net/11610/25499 |
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| Περίληψη: | The Northern Thessaly 2021 earthquake sequence changed the way we see hidden or blind faults. It occurred in Central Greece with three mainshocks of Mw6.3, Mw6.0 and Mw5.6 on 3, 4 and 12 March, respectively. Serious damages were recorded and one indirect death in the villages of the area. The importance of the sequence is due to the highlighting of several features of the broader area’s geological and tectonic environment.
This thesis is focused on the modelling of the Zarkos Fault Zone which is a hidden fault that was activated during the Northern Thessaly 2021 earthquake sequence. According to the InSAR images, it is situated in the mountainous area of Zarkos Mountains inside the Pelagonian nappe’s Triassic–Jurassic recrystallized carbonates and alternations of Paleozoic gneisses and schists that bear evidence of Alpine deformation. Surfaces of the Zarkos Fault Zone are associated with the Pliocene-Early Pleistocene NE-SW trending extension, while today’s active N-S extension has formed the E-W trending normal active faults of the broader area. At the hanging wall, it is maintained by the narrow graben-valley of Titarisios River that is filled with Neogene-Quartenary deposits.
According to our 3D modelling, the Zarkos Fault Zone comprises 4 synthetic fault surfaces of 33.5km total length and ~13km maximum depth, with an average dip of ~55o towards NE, while the dip of the major surface is at 50o. Our model results from the combination of the earthquake focuses or hypocentres of Kassaras et al. (2022) relocated catalogue and a detailed 2D mapping. For the mapping, we utilize the available InSAR images along with geological and geomorphological data.
The bidirectional propagation of the earthquake sequence begins with the two mainshocks on the major surface of the Zarkos Fault Zone, while three more synthetic surfaces are activated at its NW and SE tips. A projection of the hypocentres on the average rectangular best-fit plane is used for the detailed analysis of their spatiotemporal evolution and their correlation with our 3D model surfaces.
Examining our 3D model of the Zarkos Fault Zone and correlating it with previous models and suggestions indicates a general agreement, especially with those that are based on the same relocated catalogue, while it supports the theory of the activation of a hidden or blind low-angle fault. The main argument that remains is the dip direction of the surface associated with the 3rd mainshock occurrence on 12 March (Mw5.6), which is demonstrated as antithetic in other works.
Despite the complexity and short-timescale interactions between the multiple fault surfaces of the Zarkos Fault Zone, the Northern Thessaly 2021 earthquake sequence highlights the significant role of the structures inherited from previous deformational phases that are considered inactive. Fault growth is a continuous process resulting in fault zones that may be composed of surfaces originating from several stages of deformation and capable of giving strong earthquakes. A better understanding of these systems that may be blind, hidden or unmapped is crucial for future seismic hazard assessment studies. |
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