Geodetic Model of the March 2021 Thessaly Seismic Sequence Inferred from Seismological and InSAR Data

Abstract

In this work, we propose a geodetic model for the March 2021 Thessaly seismic sequence (TSS). We used the interferometric synthetic aperture radar (InSAR) technique and exploited a dataset of Sentinel-1 images to successfully detect the surface deformation caused by three major events of the sequence and constrain their kinematics, further strengthened by seismic data analysis. Our geodetic inversions are consistent with the activation of distinct blind faults previously unknown in this region: three belonging to the NE-dipping normal fault associated with the Mw 6.3 and Mw 6.0 events, and one belonging to the SW-dipping normal fault associated with the Mw 5.6, the last TSS major event. We performed a Coulomb stress transfer analysis and a 1D pore pressure diffusivity modeling to investigate the space–time evolution of the sequence; our results indicate that the seismic sequence developed in a sort of domino effect. The combination of the lack of historical records of large earthquakes in this area and the absence of mapped surface features produced by past faulting make seismic hazard estimation difficult for this area: InSAR data analysis and modeling have proven to be an extremely useful tool in helping to constrain the rupture characteristics.

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

“…Compared with the intersecting fault segments proposed by De Novellis et al. (2021), two adjacent faults which do not cross each other and situate ∼2 km farther west are well constrained based on the coseismic observation (Figures 2b, S2 in Supporting Information ). Considering that the major slip on the secondary fault has reached the northern edge of the assumed rupture plane (Figure 3), we do a test for the secondary fault length with the purpose to explore the accurate boundaries between adjoining fault segments.…”

“…Although the techniques used by De Novellis et al. (2021) and Kassaras et al. (2022) for the relocated aftershocks differ, this aftershocks‐identified lineament structure is robust (Figure 3b).…”

“…Compared with that a single fault model of the Tyrnavos earthquake proposed by the previous published studies (Ganas et al., 2021; Papadopoulos et al., 2021; Tolomei et al., 2021) leaves a large unfitted residual, De Novellis et al. (2021) considered a two‐fault model to retrieve coseismic slip of the Tyrnavos event. However, the interferograms they used cover combined coseismic signals of both the Tyrnavos and Elassona earthquakes.…”

“…Large gray arrows indicate the regional extension direction. Black circles are relocated aftershocks between 3 March and 26 April 2021 (De Novellis et al., 2021). Dashed magenta line shows the aftershocks‐identified fault while thick blue line indicates the fault trace fitted by relocated aftershock in Figure 1e.…”

Editorial for the Special Issue: “Ground Deformation Patterns Detection by InSAR and GNSS Techniques”

“…Several studies included in this Special Issue focused on the co-seismic deformation related to moderate to large earthquakes. De Novellis et al [4] focused on the March 2021 Thessaly seismic sequence (Central Greece) highlighting the activation of unknown distinct blind fault segments in a sort of domino effect within the seismogenic crustal volume. Caporali et al [5] analyzed the seismic sequence of November 2019 in Albania and inferred a NE-dipping reverse seismogenic fault located at a depth of 8 ± 2 km.…”