Abstract
We investigate an earthquake sequence involving an Mw = 4.6 mainshock on 2 December 2020, followed by a seismic swarm in July–October 2021 near Thiva, Central Greece, to identify the activated structures and understand its triggering mechanisms. For this purpose, we employ double-difference relocation to construct a high-resolution earthquake catalogue and examine in detail the distribution of hypocenters and the spatiotemporal evolution of the sequence. Furthermore, we apply instrumental and imaging geodesy to map the local deformation and identify long-term trends or anomalies that could have contributed to stress loading. The 2021 seismic swarm was hosted on a system of conjugate normal faults, including the eastward extension of the Yliki fault, with the main activated structures trending WNW–ESE and dipping south. No pre- or coseismic deformation could be associated with the 2021 swarm, while Coulomb stress transfer due to the Mw = 4.6 mainshock of December 2020 was found to be insufficient to trigger its nucleation. However, the evolution of the swarm is related to stress triggering by its major events and facilitated by pore-fluid pressure diffusion. The re-evaluated seismic history of the area reveals its potential to generate destructive Mw = 6.0 earthquakes; therefore, the continued monitoring of its microseismicity is considered important.
Highlights
Greece is located at the southeastern margin of Europe, a region with rich localized seismotectonic phenomena, a result of the convergence between the Eurasian and African tectonic plates
Geological, and seismological surveys have revealed that the N–S to NE–SW extensional tectonic regime of Central Greece in the Quaternary is a result of the back-arc extension between the Hellenic arc and the transtensional tectonic regime of the North Aegean [3–5]
The pre- and coseismic deformation of the Thiva area was investigated based on MT-Interferometric Synthetic Aperture Radar (InSAR) results using interferometric data from the Sentinel-1 A and B satellites of the Copernicus program
Summary
Greece is located at the southeastern margin of Europe, a region with rich localized seismotectonic phenomena, a result of the convergence between the Eurasian and African tectonic plates. These processes are expressed through intense deformation and high seismicity along thrust, strike-slip, and normal faults [1,2]. Moment tensor inversion yielded a normal focal mechanism with strike N106◦ E, dip 31◦ , and rake −81◦ [36] The analysis of both geodetic and seismological data indicated an uncommonly shallow depth of approximately 2 km for the main event. The deformation study resulted from the joint analysis of local GNSS data and satellite aperture radar interferometry (InSAR) products
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