This work deals with the effects of the 17.11.2015 earthquake with Mw6.4 occurred onshore at the SW part of Lefkada Island. The earthquake produced a large co-seismic horizontal displacement u=40 cm towards a SSW direction (N210), recorded at a near-field, permanent GPS station of NOA (PONT). Extensive geo-environmental and limited structural impacts were caused. Seismic effects have been extensively investigated during several in-situ surveys conducted by our research group and a thorough damage databank was constructed. Comparisonwith damage due to the previous strong event with Mw=6.2 occurred on 14.8.2003, showed that the effects of the current quake were significantly lower.Geo-environmental effects were observed throughout the western flanks of the mountain massif of the mainland, related with slope failures, rock falls, rock mass slides, leading thus to significant damage of several vital infrastructures. The building stock of the island comprising both modern and traditional buildings exhibited notable seismic performance during this earthquake. Structural damage was concentrated in the epicentral area where macroseismic intensity was assessed VIII, based on registered damage and vulnerability. The analysis of 3D strong ground motion recordings at two permanent accelerometric stations on the island and of the GNSS 1 Hz three-component data at PONT indicate directional dynamic effects, parallel with the T- principal axis of the event’s stress field and the regional slope dip that may likely have triggered extensive landslides. Moreover, the ground motion pattern indicates a rupture complexity involving two discrete sources. Besides the exceptional behavior of the buildings across the island, the spectral content of the strong ground motion has been found to be discrete from the elastic response of the low-rise traditional constructions, thus favoring amenablestructural damage distribution.The damage databank compiled in this work has been employed into a holistic building-by-building GIS scheme applying a vector base-map of the buildings footprints in the epicentral area available by the analysis of optical satellite imagery, undertaken within the framework of the RASOR project (http://www.rasor-project.eu). Thereafter, the poly-thematic outcome of the present study may be considered a valuable tool for the scientific community toward studying the seismic risk of Lefkada.

We analyzed a large number of focal mechanisms and relocated earthquake hypocenters to investigate the geodynamics of western Greece, the most seismically active part of the Aegean plate-boundary zone. This region was seismically activated multiple times during the last decade, providing a large amount of enhanced quality new information that was obtained by the Hellenic Unified Seismological Network (HUSN). Relocated seismicity appears concentrated above 25 km depth, exhibiting spatial continuity along the convergence boundary andbeing clustered elsewhere. Earthquakes are confined within the accreted sediments escarpment of the down-going African plate against the un-deformed Pindos hinterland. The data arrangement shows that Pindos constitutes a seismic boundary along which large stress heterogeneities occur. Surprisingly, in Cephalonia no seismicity related with the offshore Cephalonia Transform Fault (CTF) is observed. Onshore, N-S crustal extension dominates, while in central and south Peloponnesus the stress field appears rotated by 90°. Shearing-stress obliquity by 30° is indicated along the major strike-slip faults, consistent with clockwise crustal rotation. Within the lower crust, the stress field appears constrained by plate kinematics and the distributed deformation, which guide the geodynamics of the area.Seismic velocity anomalies have been resolved by regional body-wave traveltime tomography applying an iterative tomographic inversion scheme using phase data from more than 5,000 seismic events recorded by the Hellenic Unified Seismological Network (HUSN), analyzed by the Seismological Laboratory of the Universityof Athens. Preliminary 3D tomographic models indicate the presence of gross structures related with Pindus hinterland, the Tethys subduction beneath the Aegean, and shear zones related with the CTF and the Andravida fault. A predominant NE-SW oriented low velocity zone in central Peloponnesus is related with the rotation of the extensional stress field and dextral strike-slip faulting.

A catalogue of relocated earthquake hypocenters and focal mechanisms was constructed and evaluated in order to examine the tectonics of the western Hellenic Arc. The major part of the analysed dataset includes seismic activity that was recorded during the last decade. This is due to the occurrence of several moderate to strong earthquakes in the area and to the integration of the Hellenic Unified Seismological Network (HUSN), which provided adequate coverage with high quality waveform records that were analyzed by the Seismological Laboratory ofthe University of Athens. Additionally, phase data available by local networks were employed. The concept of double differences was applied to achieve improved relative hypocentral locations. Relocated seismicity appears concentrated at depths above 25 km, exhibiting spatial continuity along the convergence boundary and being clustered elsewhere. Earthquakes are confined within the accreted sediments escarpment of the down-going African plate against the un-deformed Pindos hinterland.Stress tensor inversion of ~2000 relocated focal mechanisms reveals predominantly strike-slip faulting in NNE-SSW to NE-SW direction and normal faulting in E-W or N-S directions. The heterogeneity of the stress field appears to be unusually high, particularly in the region of the northernmost tip of the Hellenic subduction and in thevicinity of the Cephalonia-Lefkada transform fault zone, an area of high seismic risk that was activated recently, with the generation of two strong earthquakes of Mw=6.1 and 5.9 at the western part of the Cephalonia Island in January-February 2014 and an Mw=6.4 event that occurred onshore SW Lefkada Island in November 2015. The stress field distribution implies that Pindos constitutes a seismic boundary along which large heterogeneities occur. Onshore western Greece, N-S crustal extension dominates, while in central and south Peloponnesus the stress field appears rotated by 90°. Shearing-stress obliquity by 30° is indicated along the major strike-slip faults. At larger depths, within the lower crust, the stress field becomes more homogeneous, consistent with well-known large scale kinematics of the Aegean region.

This work describes the outcome of two field surveys in Lefkada Island, after the 17.11.2015 earthquake of Mw6.4 at its southwestern peninsula. Geo-environmental effects were observed throughout the western flanks of the mountain massif, parallel to the activated fault. Structural damage was mainly observed in the epicentral area where macroseismic intensity was assessed as VIII, based on registered damage and assumed vulnerability per building typology. Both modern and traditional buildings exhibited notable seismic performance. The distribution of the damage per building category present in the affected area is presented, based on site surveys and post-seismic usability characterization by the local Earthquake Rehabilitation Organization. The survey highlights the frequent presence of the so-called “pontelo” dual system at both ground floor and two-story stone masonry buildings at the western mountain villages. This structural type, unique within the Greek territory, revealed significant seismic performance and the need of engineering restoration measures is underlined.

This region of western Greece has been frequently activated during the last decade, providing a large amount of enhanced quality new seismic information that was recorded by the Hellenic Unified Seismological Network (HUSN). In this work, the results of earthquake relocation, stress inversion and seismic traveltime tomography are presented, towards investigating the geodynamics of the study area. Inversion of ~2300 focal mechanisms indicates obliquity by 30 ̊ between shearing and the maximum horizontal stress along the major strike-slip faults, consistent with clockwise crustal rotation. Within the lower crust, the stress field appears to be constrained by larger scale deformation. Seismic velocity anomalies have been resolved by regional body-wave traveltime tomography, applying an iterative tomographic inversion scheme using phase data from more than 5000 seismic events. Preliminary 3D tomographic models indicate the presence of gross structures related with the western Hellenic Trench, the Cephalonia Transform Fault (CTF), the Aitoloakarnania shear zone, the Corinth Gulf and the Messinia graben. Dipping towards the east and segmentation of CTF between Cephalonia and Lefkas is evidenced by the resolved anomalies while a predominant NE-SW oriented low velocity zone observed in central Peloponnesus, related with dextral strike-slip faulting, marks a 90° rotation of the extensional stress direction that is found to occur at both sides.

We analyzed a large number of focal mechanisms and relocated earthquake hypocenters to investigate the geodynamics of western Greece, the most seismically active part of the Aegean plate-boundary zone. This region was seismically activated multiple times during the last decade, providing a large amount of enhanced quality new information that was obtained by the Hellenic Unified Seismological Network (HUSN). Relocated seismicity using a double-difference method appears to be concentrated above ∼35 km depth, exhibiting spatial continuity along the convergence boundary and being clustered elsewhere. Earthquakes are confined within the accreted sediments escarpment of the down-going African plate against the un-deformed Eurasian hinterland. The data arrangement shows that Pindos constitutes a seismic boundary along which large stress heterogeneities occur. In Cephalonia no seismicity is found to be related with the offshore Cephalonia Transform Fault (CTF). Onshore, NS crustal extension dominates, while in central and south Peloponnesus the stress field appears rotated by 90°. Shearing-stress obliquity by 30° is indicated along the major strike-slip faults, consistent with clockwise crustal rotation. Within the lower crust, the stress field appears affected by plate kinematics and distributed deformation of the lower crust and upper mantle, which guide the regional geodynamics.

Damage scenarios are necessary tools for stakeholders, in order to prepare protection strategies and a total emergency post-earthquake plan. To this aim, four seismic hazard models were developed for the city of Kalamata, according to stochastic simulation of the ground motion, using site amplification functions derived from ambient noise HVSR measurements. The structural vulnerability of the city was assessed following an empirical macroseismic model, developed for the European urban environment (EMS-98). The impact of the vulnerability due to the seismic hazard potential is also investigated by means of synthetic response spectral ratios at 108 sites of the city. The expected damage grade per building block, is calculated by combining vulnerability with the respective seismic intensities, derived for the four seismic sources. The importance of the followed methodology for implementing microzonation studies is emphasized, since the expected influence of the ground motion amplification due to local soil conditions has been approximated in detail. Moreover, new fragility curves for the main structural types in Kalamata are proposed for each seismic scenario.

Strong motion data recorded during the 15-year operation of the CORinth Gulf Soft Soil Array (CORSSA) in the highly seismic region of Aegion have been homogenized and organized in a MySQL database. In the present work we describe the contents of the database and the web portal through which these data are publicly accessible. CORSSA comprises one surface and four downhole 3-D broadband accelerometric stations. It was installed in 2002, in the framework of European project CORSEIS, aiming at gathering data for studying site effects, liquefaction, and non-linear behaviour of soils, as well as earthquake source properties. To date, the array has recorded 549 local and regional events with magnitudes ranging from 1.1 to 6.5. Although the vast majority of the recorded events caused weak ground motion at the CORSSA site, the scientific value of the data set pertains to the sparsity of this kind of infrastructure in most parts of the world.