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On 2 December 2020 10:54 UTC a shallow earthquake of MW (NOA) = 4.6 occurred near the village of Kallithea (to the east of Thiva), central Greece, which, despite its modest size, was locally damaging. Using InSAR and GNSS data, we mapped a permanent change on the ground surface, i.e., a subsidence of 7 cm. Our geodetic inversion modelling indicates that the rupture occurred on a WNW–ESE striking, SSW-dipping normal fault, with a dip-angle of ~ 54°. The maximum slip value was 0.35 m, which was reached at a depth of about 1100 m. The analysis of broadband seismological data also provided kinematic source parameters such as moment magnitude MW = 4.6 (± 0.1), rupture area 6.3 km2 and mean slip 0.16 m, which agree with the values obtained from the geodetic model. The effects of the earthquake were disproportionate to its moderate magnitude, probably due to its unusually shallow depth (slip centroid at 1.1 km) and the high efficiency of the earthquake (radiation efficiency η = 0.62). The geodetic data inversion also indicates that within the uncertainty limits of the technique, three scenarios are possible (a) the earthquake responsible for the mapped surface deformation may have occurred on a ~ 2-km long, blind normal fault different from the well-known active Kallithea normal fault or (b) could have occurred along a secondary fault that branches off the Kallithea fault or (c) it may have occurred along the Kallithea fault itself, but with its geometrical configuration could not be modelled with available data. We have also concluded that with a high dip-angle Kallithea Fault forward model it is not possible to fit the geodetic data. The rupture initiated at a very shallow depth (1.1 km) and it could not propagate deeper possibly because of a structural barrier down-dip. The 2020 event near Kallithea highlighted the structural complexity in this region of the Asopos Rift valley as the reactivation of the WNW–ESE structures indicates their significant role in strain accommodation and that they still represent a seismic hazard for this region. [ABSTRACT FROM AUTHOR]

We present a kinematic slip model and a simulation of the ensuing tsunami for the 2020 M w 7.0 Néon Karlovásion (Samos, Eastern Aegean Sea) earthquake, generated from a joint inversion of high-rate GNSS, strong ground motion and InSAR data. From the inversion, we find that the source time function has a total duration of ∼20 s with three peaks at ∼4, 7.5 and 15 s corresponding to the development of three asperities. Most of the slip occurs at the west of the hypocentre and ends at the northwest downdip edge. The peak slip is ∼3.3 m, and the inverted rake angles indicate predominantly normal faulting motion. Compared with previous studies, these slip patterns have essentially similar asperity location, rupture dimension and anticorrelation with aftershocks. Consistent with our study, most published papers show the source duration of ∼20 s with three episodes of increased moment releases. For the ensuing tsunami, the eight available gauge records indicate that the tsunami waves last ∼18–30 hr depending on location, and the response period of tsunami is ∼10–35 min. The initial waves in the observed records and synthetic simulations show good agreement, which indirectly validates the performance of the inverted slip model. However, the synthetic waveforms struggle to generate long-duration tsunami behaviour in simulations. Our tests suggest that the resolution of the bathymetry may be a potential factor affecting the simulated tsunami duration and amplitude. It should be noted that the maximum wave height in the records may occur after the decay of synthetic wave amplitudes. This implies that the inability to model long-duration tsunamis could result in underestimation in future tsunami hazard assessments. [ABSTRACT FROM AUTHOR]

Remains of past sea levels such as tidal notches may provide valuable information for the investigation of relative sea-level changes (RSL) of eustatic/tectonic origin. In this review, we focus on case studies of coastal changes from the Corinth Gulf, where impacts of past earthquakes can be traced through various indicators. The southern coast has undergone a tectonic uplift during the Holocene, whereas the northern coast has undergone subsidence. The magnitude of RSL fall in the south Corinth Gulf is larger than RSL rise in the north. Exploiting previous measurements and datings, we created a geodatabase regarding the relative sea-level changes of the whole gulf, including geodetic data based on permanent GNSS observations. The combination of geomorphological (long-term) and geodetic (short-term) data is a key advance for this area, which is characterized by fast rates of N-S crustal extension and strong earthquakes. The joint dataset fits the tectonic model of an active half-graben where the hanging wall (northern coast) subsides and the footwall (southern coast) is uplifted. The highest uplift rates (3.5 mm/year) are near Aigion, which indicates an asymmetric localization of deformation inside this active rift. [ABSTRACT FROM AUTHOR]

We present a comprehensive analysis of geodetic data, including InSAR and GNSS, to assess the interseismic deformation of the Paliki peninsula in western Cephalonia, Greece. The region is prone to frequent earthquakes, due to its proximity to the Cephalonia Transform Fault (CTF), a 140 km long dextral strike-slip fault (striking NNE-SSW) that accommodates the relative motion between the Apulian and Aegean lithospheric plates. Our analysis covers the period from 2016 to 2022 and leverages LiCSBAS, an open-source package, for InSAR time series analysis with the N-SBAS method. The results of the InSAR analysis demonstrate deformation rates between 2 and 5 mm/yr in the line-of-sight (LOS) direction of the satellite. We constructed E -W velocity profiles that provided a velocity gradient terminating against the outcropping trace of the seismic fault of the 3 February 2014 earthquake (M6.1) near Atheras. This geodetic evidence indicates a ∼ 1 mm/yr minimum aseismic slip (fault creep) motion along the February 2014 seismic fault, during 2016–2022. Positive LOS values in both satellite imaging geometries show that the coastal town of Lixouri experiences uplift of 1 mm/yr. East-West velocity cross-sections across western Cephalonia including Gulf of Argostoli reveal several velocity discontinuities, possibly bounded by active faults and/or landslides. The E -W shortening rate between Lixouri and Argostoli areas amounts to 1.5 mm/yr corresponding to −187 ns/yr (nanostrain/yr) of tectonic strain. Our results suggest a complex deformation pattern on the Paliki peninsula with strain accumulation along strike-slip and reverse-slip faults. We also inverted GNSS velocities from Italy and Greece, across the Cephalonia segment of CTF (assuming elastic half-space) and obtained a locking depth of 13 km, and a slip rate of 17.3 ± 0.8 mm/yr. • We mapped a 1.5 mm/yr E -W shortening between Paliki and central Cephalonia. • The Paliki peninsula is uplifting with an average rate of 1 mm/yr. • We provide a slip rate of the Cephalonia Transform Fault of 17.3 ± 0.8 mm/yr. [ABSTRACT FROM AUTHOR]

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Here, we present the results of a kinematic slip model of the 2020 M w 6.7 Doğanyol-Sivrice, Turkey Earthquake, the most important event in the last 50 yr on the East Anatolian Fault Zone. Our slip model is constrained by two Sentinel-1 interferograms and by 5 three-component high-rate GNSS (Global Navigation Satellite System) recordings close to the earthquake source. We find that most of the slip occurs predominantly in three regions, two of them at between 2 and 10 km depth and a deeper slip region extending down to 20 km depth. We also relocate the first two weeks of aftershocks and find a distribution of events that agrees with these slip features. The HR-GNSS recordings suggest a predominantly unilateral rupture with the effects of a directivity pulse clearly seen in the waveforms and in the measure peak ground velocities. The slip model supports rupture propagation from northeast to southwest at a relatively slow speed of 2.2 km s−1 and a total source duration of ∼20 s. In the absence of near-source seismic stations, space geodetic data provide the best constraint on the spatial distribution of slip and on its time evolution. [ABSTRACT FROM AUTHOR]

On November 17, 2015 07:10:07 UTC a strong, shallow Mw6.5 earthquake, occurred on the island of Lefkada along a strike-slip fault with right-lateral sense of slip. The event triggered widespread environmental effects at the south and western part of the island while, the intensity and severity of these earthquake-induced deformations is substantially decreased towards the eastern part of the island. Relocation of seismicity and inversion of geophysical (GPS, InSAR) data indicate that the seismic fault runs parallel to the west coast of Lefkada, along the Aegean – Apulia plate boundary. The fault plane strikes N20 ± 5°E and dips to east with an angle of about 70 ± 5°. Coseismic deformation was measured in the order of tens of centimeters of horizontal motion by continuous GPS stations of NOANET (the NOA GPS network) and by InSAR (Sentinel 1 A image pairs). A coseismic uniform-slip model was produced from inversion of InSAR data and permanent GPS stations. The earthquake measured Mw = 6.5 using both the geodetic moment produced by the slip model, as well as the PGD relation of Melgar et al. (2015, GRL). In the field we observed no significant vertical motion of the shoreline or surface expression of faulting, this is consistent with the predictions of the model. The interferograms show a large decorrelation area that extends almost along all the western coast of Lefkada. This area correlates well with the mapped landslides. The 2003–2015 pattern of seismicity in the Ionian Sea region indicates the existence of a 15-km seismic gap offshore NW Cephalonia. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present an updated velocity field in central Greece based on cGPS data from 33 stations. [•] Clockwise rotation dominates, with the largest values across the central Gulf of Corinth and across the Sperchios rift. [•] Attica and Corinth belong to the same crustal block. [•] The boundary consists of the Kaparelli–Asopos valley faults. [•] We find extension across “rigid” North Peloponnese taken by normal faults in the greater Kalavryta region. [ABSTRACT FROM AUTHOR]

On 18 January 2010, 15:56 UTC, a M = 5.1 (National Observatory of Athens; NOA) earthquake occurred near the town of Efpalion (western Gulf of Corinth, Greece), about 10 km to the east of Nafpaktos, along the north coast of the Gulf. Another strong event occurred on 22 January 2010, 00:46 UTC with M = 5.1 (NOA) approximately 3 km to the NE of the first event. We processed the seismological and geodetic data to examine fault plane geometry, dip direction, and earthquake interactions at the western tip of the Corinth rift. Our data include relocated epicenters of 1,760 events for the period January-June 2010 and daily global positioning system observations from the Efpalio station for the period 1 December 2009-1 March 2010. We suggest that the first event ruptured a blind, north-dipping fault, accommodating north-south extension of the Western Gulf of Corinth. The dip direction of the second event is rather unclear, although a south dip plane is weakly imaged in the post-22 January 2010 aftershock distribution. A Coulomb stress model based on homogeneous slip distribution of the first event showed static stress triggering of the second event of the order of 22-34 KPa that was transferred along the plane of failure. We also point out the existence of north dipping, high-angle faults at 10-15 km depths, which were reactivated because of Coulomb stress transfer, to the west and south of Efpalion. The January 2010 earthquakes ended a 15-year-old quiescence in that area of the Gulf. The crustal volume near Efpalion was also characterized by b values in the range 0.6-0.8 (1970-2010 period). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a joint analysis of seismological and Global Navigation Satellite System (GNSS) data of the seismic sequence that started on October 25, 2018 with a shallow M w = 6.7 earthquake offshore Zakynthos (Ionian Sea, Greece). The inversion of the GNSS data shows the activation of a N-S striking thrust/oblique-slip fault at the African-Aegean plate interface with a length of ∼26 km, and depth shallower than 15 km. The fault-plane geometry is well constrained by GNSS with a low-dip angle (23°), and dip-direction towards east. This is consistent with the distribution of the relocated aftershocks (1811 events). Our analysis indicates that the October 25, 2018 event ruptured the Hellenic megathrust. This event highlights the high degree of seismic coupling in the western region of the Hellenic Arc. It also highlights the "strong" nature of the subducting slab with the occurrence of "locked" patches under the Ionian seafloor that fail during large, reverse/oblique-slip earthquakes. The latest, shallow seismic events of the western Hellenic arc (1976 Zakynthos, 1997 Strofades, 2018 Zakynthos) point to a sequence of low-angle events along the plate interface with most of co-seismic deformation taken up by the upper (Aegean) plate. The GNSS data also point to a similar pattern between the co-seismic strain release and the long-term (interseismic) strain accumulation along the west Hellenic Arc. [ABSTRACT FROM AUTHOR]

We identify the source of the Mw = 6.4 earthquake that rocked north-central Albania on November 26, 2019 02:54 UTC. We use synthetic aperture radar interferograms tied to the time series of coordinates of two permanent Global Navigation Satellite System (GNSS) stations (DUR2 and TIR2). We model the source by inverting the displacement data. Assuming in our model a half-space elastic medium and uniform slip along a rectangular fault surface, we invert the 104 picked measurements on a couple of ascending and descending interferograms to calculate the parameters of the fault. All inversions made with different input parameters converge towards a stable and robust solution with root mean square (r.m.s.) residual of 5.4 mm, thus ~1/5 of a fringe. They reveal that the earthquake occurred deep in the crust on a low-angle fault (23°) dipping towards east with a centroid at 16.5 km depth. The best-fitting length and width of the fault are 22 and 13 km, and the reverse slip, 0.55 m. The seismic moment deduced from our model agrees with those of the published seismic moment tensors. This geometry is compatible with a blind thrust fault that may root on the main basal thrust, i.e., along the thrust front that separates Adria–Apulia from Eurasia. It is notable that there is a 123 ns yr−1 active shortening of the crust between the GNSS stations DUR2-TIR2 (equivalent to a shortening rate of 3.6 mm yr−1), and roughly in the east–west direction. Given this amount of strain the recurrence time of M6+ earthquakes along this fault should be of the order of 150 years. [ABSTRACT FROM AUTHOR]

The Kephalonia Transform Zone (KTZ) is a seismically active dextral transform fault decoupling the extensional deformed area of the Ionian Abyssal Plain and the compressional deformed area of the Mediterranean Ridge. We estimate a prominent steady state strain rate of 225 ± 20 nstrain/year across the KTZ from the mean velocities of permanent Global Navigation Satellite System (GNSS) stations in East Italy and West Greece, which confirms previous estimates. Based on the regional statistical seismicity and using the local Gutenberg–Richter relation we investigate the energetic balance between stress accumulated as a consequence of the continuous dextral shear deformation, and the average stress released by shallow seismicity. If the maximum expected magnitude is M w = 7.4, the estimated a and b parameters of the local Gutenberg–Richter relation and the geodetically determined shear-strain rate set an upper limit to the regional stress drop ∆ σ ≤ 0.4 MPa. We verify these values by analyzing a seismic sequence on the KTZ between January and February 2014, which culminated in the M w = 6.09 event of Jan. 26, and the M w = 6.14 event of Feb. 3. The estimated epicenters lie within a few kilometers from each other, on the western side of the Kephalonia Island, at a hypocentral depth ≤ 10 km. The measured coseismic displacements of GNSS stations in this area fit the expected surface dislocation, which can be predicted for an elastic half-space using the measured fault-plane solutions as input. If the hypocenters of the aftershocks are taken as indicator of optimal dextral shear-stress orientation, then a low regional deviatoric stress of 0.4 MPa, that is comparable with the maximum regional stress drop estimated above, is required for the Coulomb stress to match the pattern of the aftershocks of the 2014 sequence. As a consequence, we conclude that the regional deviatoric stress and the seismically released shear stress are in close balance in the KTZ seismic province. [ABSTRACT FROM AUTHOR]