We investigate the seismotectonics of Western Greece using data recorded by a local network of 15 short-period seismic stations. They were installed in July 2016 in order to densify the permanent Hellenic Unified Seismological Network (HUSN), which is sparse in this region. The study area covers the islands of Zakynthos and Cephalonia in addition to Western Peloponnese and Akarnania. The temporary network remained in operation until May 2017 and recorded roughly 4000 events that were analyzed using automatic P- and S-wave phase picking algorithms. The procedure yielded 1200 local earthquakes located using the Hypoinverse code and five 1D velocity models optimized by the Velest error minimization technique. The events were further relocated using the HypoDD package. We computed 100 focal mechanisms for magnitudes down to ML 2.3 using first motion polarities. The rose diagrams and stress axes imply transpressional tectonics. By combination of the focal mechanisms, historical earthquakes and the recorded patterns of (micro)seismic activity, seismogenic structures were detected and emphasized. The data allowed us to construct a conceptual and updated tectonic model of the Ionian Akarnania crustal Block (IAB) articulated around 4 major strike-slip structures : -The Cephalonia Transform Fault has been recognized as a large deformation zone that intersects with left-lateral NW-striking strike-slip faults and is the western margin of the IAB. -The Kyllini Cephalonia Fault highlighted by this study intersects with the Movri-Amiliada Fault Zone. These structures are proposed to be the south-western and south-eastern boundaries of the IAB. -The NW-striking sinistral Katouna-Stamna Fault zone and the Ambracian Gulf depict the north-eastern and north margin of the block. During the deployment we also recorded intense seismic activity southwest of the island of Zakynthos. These events most likely occurred on an activated structure of the upper plate that we link with the large 2018 Mw 6.7 megathrust earthquake that occurred 20 km towards the south.

On 2017 and 2018 four strong/moderate earthquakes occurred at shallow focal depths in the East Mediterranean. They share a common characteristic, which is that a large part of the induced ground deformation is offshore, thus a part of the deformation footprint is missing. Assuming that the deformation source of an earthquake can be modelled by the slip on a rectangular fault buried in an elastic and homogenous halfspace and through inversion on GNSS and multitrack InSAR (with different weight in each case) we modelled the deformation sources and calculated their fault parameters. Seismological data as well as the geological context exploited to assist the initialization of some parameters in the inversion andvalidate the results. This study demonstrate the efficiency and the contribution of the space geodesy to the seismology, even in such adverse conditions.

Earthquake scenarios were applied towards seismic risk assessment in the earthquake prone city of Aigion (W. Corinth Gulf), by combining deterministic seismic hazard and empirical structural vulnerability. Ground motions for three hazardous fault sources for Aigion were generated using a finite source stochastic simulation technique, taking into account the well-established seismotectonics of the area and site effects derived from ambient noise horizontal-to-vertical-spectral-ratios (HVSR). Validation of the parameters of the stochastic simulation and the estimated damage was performed with respect to real recordings and the damage database of a past seismic event in the area. Vulnerability was assessed empirically for an exposure model comprising 3200 buildings, compiled with on site and remoted techniques. The European Macroseismic Scale (EMS-98) was used to describe the ground motion severity in terms of macroseismic intensity and the taxonomy of the building stock into 7 structural types. Seismic risk was spatialized using GIS mapping tools on a building block scale in terms of EMS-98 damage grades and their maximum probability of occurrence. The obtained risk assessment models indicate that the northeastern and partly the southern part of Aigion are more susceptible to damage, in accordance with damage distribution from the most recent Mw6.4 disastrous earthquake for the city in 1995, the site amplification inferred from HVSR, and the assessed vulnerability of the constructions. Nevertheless, the current building stock demonstrates significantly enhanced seismic behaviour, due to rehabilitation after the 1995 earthquake. Despite unavoidable uncertainties, intrinsic to both the method and data, the herein seismic risk assessment appears realistic and consistent, thus allowing its exploitation towards loss estimation and mitigation scenarios.

A massive dataset of over 1900 focal mechanisms of crustal earthquakes with M ≥ 3.5 in the Greek region was employed to resolve the contemporary stress-field using a damped least-squares inversion. The results are in good agreement with the strain-rate field of the Global Strain Rate Model, which was used as reference, both in terms of their principal axes orientations and expected faulting styles. Dual stress-states were identified using the Multiple Inverse Method in regions delineated by joining neighboring Area Sources of the European Seismic Hazard Model 2013 (ESHM13). North-western Greece is mostly affected by transpressional tectonics characterized by NE-SW contraction. Northern/central Greece and the Corinth Rift are dominated by E-W normal faulting, with secondary oblique-normal to strike-slip faulting at the western margin of the latter. North and central Aegean are mainly governed by transtensional regime, characterized by stable N-S extension. The stress-tensor was found to be compatible with the Fault Sources (FS) of ESHM13, in terms of orientation and expected faulting type. Differences were observed in regions of low strain-rate, such as the Southern Aegean, where left-lateral, E-W strike-slip instead of normal faulting was inferred. Discrepancies in areas with strong local heterogeneities were highlighted by anomalies in the stress-ratio, Φ, indicating transtensional regime in the pull-apart basins of Western Greece and transpressional tectonics in north-western Greece and south of Crete. The latter is characterized by stable N-S contraction, SW-NE sinistral strike-slip and E-W reverse faulting in the vicinity of the subduction zone. A low Φ, E-W oriented zone was identified along the active volcanic arc, where a remarkable 90° rotation occurs in the stress field. This rotation is related to the transition from E-W (in the north) to N-S (in the south) normal faulting in Peloponnese and Dodecanese Islands, as well as rearrangement from dextral to sinistral SW-NE strike-slip faulting in North and South Aegean, respectively.

On July 20, 2017 22:31 UTC, a strong Mwþinspace}=þinspace}6.6 earthquake occurred at shallow depth between Kos Island (Greece) and Bodrum (Turkey). We derive a co-seismic fault model from joint inversion of geodetic data (GNSS and InSAR) assuming that the earthquake can be modelled by the slip of a rectangular fault buried in an elastic and homogeneous half-space. The GNSS observations constrain well most of the model parameters but do not permit to discriminate between south- and north-dipping planes. However, the interferograms, produced from C-band ESA Sentinel 1 data, give a clear preference to the north-dipping plane. We also map surface motion away from the satellite along the Turkish coast (from Bodrum towards the east) which reached about 17 cm onshore islet Karaada. The best-fit model is obtained with a 37° north-dipping, N283°E striking normal fault, in agreement with the published moment tensor solutions. The resolved slip vector is dominantly normal with a slight component of left-lateral motion (15°). The surface projection of the seismic fault outcrops in the Gökova ridge area, a well-developed bathymetric feature inside the western Gulf of Gökova. Our geodetic model fits the pattern of the shallow, north-dipping aftershocks obtained from rigorous relocation of all available recordings in the region (about 1120 events; relocated mainshock is at 36.955°N, 27.448°E; depth at 9.2 kmþinspace}±þinspace}0.5 km). The relocated aftershocks also indicate clustering at both ends of the rupture and seismicity triggering mainly towards the east and the north, within 2 weeks following the mainshock. We also analysed regional GPS data (interseismic velocities) and obtained an extension rate of 3.2 mm/yr across the Gökova rift, along a direction N165°E.

On June 12, 2017, an Mw 6.3 earthquake struck Lesvos Island (Northeastern Aegean, Greece). Building damage was observed in its southeastern part with very heavy structural damage limited in the settlement of Vrissa. Taking into account that Vrissa is located further inland from the epicenter than other settlements with less damage, Vrissa looks like an earthquake impact paradox. For interpreting this paradox, a complete approach for damage assessment in an earthquake-affected area was applied during the first hours of the emergency response phase in order to provide crucial information to civil protection agencies. It comprises integration of building-by-building inspection, use of desktop and web GIS applications, UAV survey and digital post processing, extraction of data and information related to the buildings of the affected area, application of the European Macroseismic Scale 1998 and assignment of macroseismic intensities. Correlation of the all aforementioned data with the geological, geomorphological, geotechnical and seismological properties of the affected area along with its buildings characteristics was followed. This damage scene is attributed to the synergy of the near-field location of Vrissa, recent deposits, geotechnically unstable zones, proximity to active faults, rupture directivity phenomena and vulnerable buildings. The integration of UAV and web GIS applications during a rapid post-earthquake field macroseismic reconnaissance can potentially be considered as a methodological framework that can be applied for similar analysis in other areas affected not only by earthquakes but also by other extreme events that have the potential to cause destructive effects on the natural environment, humans and infrastructures.