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We investigate mainshock slip distribution and aftershock activity of the 8 January 2013 M = 5.7 Lemnos earthquake, north Aegean Sea. We analyse the seismic waveforms to better understand the spatio-temporal characteristics of earthquake rupture within the seismogenic layer of the crust. Peak slip values range from 50 to 64 cm and mean slip values range from 10 to 12 cm. The slip patches of the event extend over an area of dimensions 16 × 16 km. We also relocate aftershock catalog locations to image seismic fault dimensions and test earthquake transfer models. The relocated events allowed us to identify the active faults in this area of the north Aegean Sea by locating two, NE-SW linear patterns of aftershocks. The aftershock distribution of the mainshock event clearly reveals a NE-SW striking fault about 40 km offshore Lemnos Island that extends from 2 km up to a depth of 14 km. After the mainshock most of the seismic activity migrated to the east and to the north of the hypocenter due to (a) rupture directivity towards the NE and (b) Coulomb stress transfer. A stress inversion analysis based on 14 focal mechanisms of aftershocks showed that the maximum horizontal stress is compressional at N84°E. The static stress transfer analysis for all post-1943 major events in the North Aegean shows no evidence for triggering of the 2013 event. We suggest that the 2013 event occurred due to tectonic loading of the North Aegean crust. [ABSTRACT FROM AUTHOR]

In the period 2011 June–October, a tectonic swarm of nearly 1222 earthquakes occurred in the Messenia prefecture at the southwestern region of the Peloponnese Peninsula. The swarm happened in the Messenia's Upper Quaternary basin, 25 km NW of the city of Kalamata, and migrated from NNW towards SSE. The largest earthquakes occurred in 2011 August 14 (Mw = 4.8), September 14 (Mw = 4.6) and October 10 (Mw = 4.7), caused moderate structural damages mainly in old houses in four villages and produced particular unrest to the local population. We have investigated the monthly migration of the swarm using Differential Synthetic Aperture Radar Interferometry (DInSAR), presenting for the first time a very close look at the deformation evolution that may reveal an aseismic slip component of the total movement. The geodetically derived slip distribution for the first 4 months revealed that slip migrated laterally along strike (north to south) and vertically from a deep portion, at ∼2.8 km depth, to a shallow portion, at less than 0.5 km, of the fault plane, and concluded its migration towards the surface with a very shallow Mw 4.7 event of 2011 October 10 surprisingly detected by DInSAR. [ABSTRACT FROM AUTHOR]

Bathymetric and seismic data provide insights into the geomorphological configuration, seismic stratigraphy, structure, and evolution of the area between Santorini, Amorgos, Astypalea, and Anafi islands. Santorini-Amorgos Shear Zone (SASZ) is a NE-SW striking feature that includes seven basins, two shallow ridges, and hosts the volcanic centers of Santorini and Kolumbo. The SASZ initiated in the Early Pliocene as a single, W-E oriented basin. A major reorganization of the geodynamic regime led to (i) reorientation of the older faults and initiation of NE-SW striking ones, (ii) disruption of the single basin and localized subsidence and uplift, (iii) creation of four basins out of the former single one (Anafi, Amorgos South, Amorgos North, and Kinairos basins), (iv) rifting of the northern and southern margins and creation of Anydros, Astypalea North, and Astypalea South basins, and (v) uplift of the ridges. Dextral shearing and oblique rifting are accommodated by NE-SW striking, dextral oblique to strike-slip faults and by roughly W-E striking, normal, transfer faults. It is suggested here that enhanced shearing in NE-SW direction and oblique rifting may be the dominant deformation mechanism in the South Aegean since Early Quaternary associated with the interaction of North Anatolian Fault with the slab roll-back. [ABSTRACT FROM AUTHOR]

Underwater volcanoes and their linear distribution on the flanks of mid-ocean ridges are common submarine topographic structures at intermediate- and fast-spreading systems, where sufficient melt supplies are often available. Such magma sources beneath the seafloor located within a few kilometers of the corresponding ridge-axis tend to concentrate toward the axis during the upwelling process and contribute to seafloor formation. As a result, seamounts on the flanks of the ridge axis are formed at a distance from the spreading axis and distributed asymmetrically about the axis. In this study, we examined three linearly aligned seamount chains on the flanks of the KR1 ridge, which is the easternmost and longest Australian-Antarctic Ridge (AAR) segment. The AAR is an intermediate-spreading rate system located between the Southeast Indian Ridge and Macquarie Triple Junction of the Australian-Antarctic-Pacific plates. By inspecting the high-resolution shipboard multi-beam bathymetric data newly acquired in the study area, we detected 20 individual seamounts. The volcanic lineament runs parallel to the spreading direction of the KR1 segment. The geomorphologic parameters of height, basal area, volume, and summit types of the identified seamounts were individually measured. We also investigated the spatial distribution of the seamounts along the KR1 segment, which exhibits large variations in axial morphology with depth along the ridge axis. Based on the geomorphology and spatial distribution, all the KR1 seamounts can be divided into two groups: the subset seamounts of volcanic chains distributed along the KR1 segment characterized by high elevation and large volume, and the small seamounts distributed mostly on the western KR1. The differences in the volumetric magnitude of volcanic eruptions on the seafloor and the distance from the given axis between these two groups indicate the presence of magma sources with different origins. [ABSTRACT FROM AUTHOR]

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth. [ABSTRACT FROM AUTHOR]

In this contribution, we present strain-rate results from 298 permanent European GNSS stations (part of EUREF Permanent Network), operating since 1996 until 2018. The stations positions are computed with several geodetic software packages (mainly Bernese, but also GAMIT and GIPSY) and the combined positions are done with Bernese. Then we used CATREF to estimate multi-year positions and velocity solution. The available dataset comprises the velocity field extracted from the C2010 EPN solution. We calculated the strain-rate field using the open-source software STRAINTOOL (https://github.com/DSOlab/StrainTool) which uses the algorithm VISR (Velocity Interpolation for Strain Rate; Shen et al., 2015). The following products were obtained: Emax-Emin, rotational rates, 2nd invariant, shear strain rates and orientations of horizontal shear, dilatational strain rates etc. The vertical velocity component is ignored in this stage and other sources of deformation (GIA, hydrological, anthropogenic et al.) are not considered in the preliminary interpretation. We compare the results derived from different model setups (variable grid-size, distance from cell-centre, smoothing parameter etc.) and discuss the similarities and differences. Overall, our first results reproduce the gross features of tectonic deformation in Southern Europe, such as NE-SW extension across the Apennines (Italy), NNW-SSE compression across the Alboran Sea (western Mediterranean) and N-S extension in mainland Greece. Large areas of central and Northern Europe show small strain rates (less than 10 ns/yr; 2nd invariant of the tensor). We acknowledge support of this research by the project "HELPOS - Hellenic Plate Observing System" (MIS 5002697) which is implemented under the Action "Reinforcement of the Research and Innovation Infrastructure", funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund). [ABSTRACT FROM AUTHOR]

A correction to the article "The Lemnos 8 January 2013 (Mw=5.7) earthquake: fault slip, aftershock properties and static stress transfer modeling in the north Aegean Sea" in the 2014 issue is presented.

To assess whether continental extension and seismic hazard are spatially-localized on single faults or spread over wide regions containing multiple active faults, we investigated temporal and spatial slip-rate variability over many millennia using in-situ 36 Cl cosmogenic exposure dating for active normal faults near Athens, Greece. We study a ~ NNE-SSW transect, sub-parallel to the extensional strain direction, constrained by two permanent GPS stations located at each end of the transect and arranged normal to the fault strikes. We sampled 3 of the 7 seven normal faults that exist between the GPS sites for 36 Cl analyses. Results from Bayesian inference of the measured 36 Cl data implies that some faults slip relatively-rapidly for a few millennia accompanied by relative quiescence on faults across strike, defining out-of-phase fault activity. Assuming that the decadal strain-rate derived from GPS applies over many millennia, slip on a single fault can accommodate ~ 30-75% of the regional strain-rate for a few millennia. Our results imply that only a fraction of the total number of Holocene active faults slip over timescales of a few millennia, so continental deformation and seismic hazard are localized on specific faults and over a length-scale shorter than the spacing of the present GPS network over this time-scale. Thus, (1) the identification of clustered fault activity is vital for probabilistic seismic hazard assessments, and (2) a combination of dense geodetic observations and palaeoseismology is needed to identify the precise location and width of actively deforming zones over specific time periods., (© 2021. The Author(s).)