The Mw = 5.6 Kanallaki Earthquake of 21 March 2020 in West Epirus, Greece: Reverse Fault Model from InSAR Data and Seismotectonic Implications for Apulia-Eurasia Collision

Abstract

We identify the source of the Mw = 5.6 earthquake that hit west-central Epirus on 21 March 2020 00:49:52 UTC. We use Sentinel-1 synthetic aperture radar interferograms tied to one permanent Global Navigation Satellite System (GNSS) station (GARD). We model the source by inverting the INSAR displacement data. The inversion model suggests a shallow source on a low-angle fault (39°) dipping towards east with a centroid depth of 8.5 km. The seismic moment deduced from our model agrees with those of the published seismic moment tensors. This geometry is compatible with reverse-slip motion along the west-verging Margariti thrust fault that accommodates part of the convergence within the collision zone between Apulia and Eurasia. We also processed new GNSS data and estimate a total convergence rate between Apulia and Eurasia of 8.9 mm yr−1, of which the shortening of the crust between the Epirus coastal GNSS stations and station PAXO in the Ionian Sea (across the Ionian Thrust) is equivalent to ~50% of it or 4.6 mm yr−1. By back-slip modelling we found that a 60-km wide deformation zone takes up nearly most of the convergence between Apulia-Eurasia, trending N318°E. Its central axis runs along the southwest coast of Corfu, along the northeast coast of Paxoi, heading toward the northern extremity of the Lefkada island. The island of Paxoi appears kinematically as part of the Apulian plate.

The Arkalochori Mw = 5.9 Earthquake of 27 September 2021 Inside the Heraklion Basin: A Shallow, Blind Rupture Event Highlighting the Orthogonal Extension of Central Crete

“…To match the top of the modelled fault (1.2 km beneath the surface) with the scarp of the Avli fault, in the vicinity of the village of Nipiditos, requires a dip angle of ~55 • throughout the upper crust of central Crete, in agreement with the modelled fault plane (Figures 8 and 9) and cancelling the need for listric geometries updip the hypocentre as implied by [2,3]. It also requires a small (~1 km) shift in location of the relocated mainshock towards east, which is an offset feature that we have seen in several earthquake sequences in Greece (e.g., [53,76]) likely caused by heterogeneities in the crustal structure not captured by the 1-D velocity model. The Arkalochori earthquake along the Kastelli Fault Zone highlights the nearly arcparallel (E-W to WNW-ESE) extension of the Heraklion basin in central Crete as opposed to the neighbouring E-W Messara basin, to the south (Figure 2).…”

“…Certainly, GPS observations are useful or needed before and after earthquakes in the near field of earthquakes, for example to assess the secular deformations (see [23,52,76,79]) but when they are outperformed by InSAR for the assessment of the co-seismic displacement, the motivation for performing those measurements must be established. We believe there is a real value in the assessment of the secular deformations; therefore, the selection of the GPS points, their direct connection to the bedrock, their long-term stability and preservation over decades, if not centuries, should be central in the design of the benchmarks and their maintenance.…”

Ground Deformation Modelling of the 2020 Mw6.9 Samos Earthquake (Greece) Based on InSAR and GNSS Data

“…Several of the highly correlated data points in the unwrapped calibrated interferograms were down-sampled using an approach similar to [53] to facilitate the modelling. For each orbital trajectory, LOS displacement values from the calibrated interferograms were numerically extracted by manually picking selected pixels.…”

Coseismic Ground Displacement after the Mw6.2 Earthquake in NW Croatia Determined from Sentinel-1 and GNSS CORS Data

“…Many recent studies have focused to the usage of SAR technology in the estimation of ground deformation after large earthquakes: Reference [14] estimated the land displacement but without detecting the active major faults; Reference [15] highlighted the need to consider the coherence change analysis and identify the limitations of the SAR applications; others ( [16][17][18][19][20]) estimated earthquake's impact assessment based on the data derived from SAR. Furthermore, the SAR technique is now used for the study of earthquakes and has been applied around the World ( [21][22][23][24][25]) and in Europe ( [26][27][28]).…”