The tectonic setting of western Peloponnese and central Ionian Islands, Greece, is characterized by the subduction of the oceanic African plate beneath the Aegean micro-plate. The transition from subduction to continental collision in northwestern Greece is accommodated by the right-lateral Cephalonia transform fault. In this work, we exploit the recordings of a temporary seismic network composed of 15 stations operating from July 2016 until May 2017 to investigate the complex deformation of this region. Our local network fills in a major observational gap in one of the most tectonically active regions of the Hellenic arc. We detected and located more than 1200 local earthquakes and constrained five 1D optimum local velocity models. The relocated seismicity (including the aftershock sequence that followed the October 2018 Mw 6.7 earthquake offshore Zakynthos) and associated focal mechanisms constrained for the major earthquakes point out a complex crustal deformation. We propose a clockwise rotation of the Ionian Akarnania Block accommodated by major marginal strike-slip fault zones that appear segmented along their strike. Additionally, left-lateral motion is observed on the Kyllini-Cephalonia fault along a north-west direction. Finally, the seismicity recorded in north Cephalonia (offshore Myrtos and Fiskardo) suggests that the Cephalonia transform fault is a large deformation zone where secondary WNW-striking sinistral strike-slip faults occur.

{This research provides new constraints on the intermediate depth upper-mantle structure of the Hellenic lithosphere using a three-step Rayleigh-wave tomography. Broadband waveforms of about 1000 teleseismic events, recorded by ∼200 permanent broadband stations between 2010 and 2018 were acquired and processed. Through a multichannel cross-correlation technique, the fundamental mode Rayleigh-wave phase-velocity dispersion curves in the period range 30 to 90 s were derived. The phase-velocities were inverted and a 3-D shear velocity model was obtained down to the depth of 140 km. The applied method has provided 3-D constraints on large-scale characteristics of the lithosphere and the upper mantle of the Hellenic region. Highlighted resolved features include the continental and oceanic subducting slabs in the region, the result of convergence between Adria and Africa plates with the Aegean. The boundary between the oceanic and continental subduction is suggested to exist along a trench-perpendicular line that connects NW Peloponnese with N. Euboea, bridging the Hellenic Trench with the North Aegean Trough. No clear evidence for trench-perpendicular vertical slab tearing was resolved along the western part of Hellenic Subduction Zone; however, subcrustal seismicity observed along the inferred continental-oceanic subduction boundary indicates that such an implication should not be excluded. The 3-D shear velocity model supports an N-S vertical slab tear beneath SW Anatolia that justifies deepening, increase of dip and change of dip direction of the Wadati-Benioff Zone. Low velocities found at depths \< 50 km beneath the island and the back-arc, interrelated with recent/remnant volcanism in the Aegean and W. Anatolia, are explained by convection from a shallow asthenosphere.}

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.

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.

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 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.

Ten years after the occurrence of the Andravida earthquake (2008) several aspects were investigated, including its connection to neighboring spatiotemporal clusters in the following years. On 8 June 2008 at 12:25 GMT a large earthquake (Mw=6.4) occurred NE of Andravida (Greece) in an area characterized by relatively low seismicity. Nevertheless, it is worth noting that this major event was successfully predicted by a previous study, taking into account decelerating accelerating seismicity. Data recorded by the Unified Hellenic Seismological Network (HUSN)were analyzed to study the aftershock sequence and local velocity structure. The modeling of teleseismic P, SV and SH waves provided well-constrained focal mechanism solutions of the mainshock and its major aftershocks with magnitude M > 3.4. The constrained fault plane solutions represent dextral strike slip type faulting. The spatial distribution of the aftershocks, as well as the calculation of the slip distribution and Local Earthquake Tomography (LET), provided evidence that the rupture plane is the one with NE-SW direction. Surface breaks were observed inseveral sites but in most cases their direction was perpendicular to the rupture plane and can be characterized as secondary effects. The source process was characterized by unilateral rupture propagation towards the city of Patras, to the NE, where a seismic sequence was initiated after the Mw=3.9 event of the 27th December 2012 along the ENE-WSW Agia Triada normal fault.

The Gulf of Corinth (Central Greece) is among the most active tectonic rifts worldwide. This is evidenced by the high level of seismicity, the intense E-W trending normal faulting and the high extension rate in a N-S direction. Destructive earthquakes, such as the Heliki event in 373 BC, have occurred since the antiquity. Intense seismicity has also occurred during the instrumental era, with the most recent strong event being the Ms=6.2 1995 Aigion earthquake. In this work, we present the RASMON and CORSSA accelerometric arrays installed across the Gulf of Corinth by the National and Kapodistrian University of Athens (NKUA) and collaborative institutes in the frame of EU and national projects. Accelerometers were first installed in 1991 and through continuous upgrades and maintenance remain in operation to date, having recorded several thousands of high-quality acceleration time-series of local and regional earthquakes. Nowadays, the accelerometric network comprises eleven (11) three-component instruments (RASMON) and a 15-component vertical array (CORSSA) operating in trigger mode. Six stations located on the southern shore of the Gulf are online via a MOXA serial-to-TCP/IP converter. Recently, NKUA has undertaken an upgrade task of the arrays in the frame of the HELPOS project, the national analog to the EU-wide EPOS project. Upgrade includes conversion of the serial Etna/K2 Kinemetrics instruments into SeedLink servers using Raspberry PIs. Therefore, via Earthworm software, tunneling to NKUA and NTP timing will be plausible. To this aim, tests are currently implemented yielding promising perspective.

On July 20, 2017 22:31 UTC, a strong Mw = 6.6 earthquake occurred at shallow depth between Kos (Greece) and Bodrum (Turkey).We derive a co-seismic fault model from joint inversion of geodetic data (GNSS and InSAR).We assume that the earthquake can be modelled by the slip on a rectangular fault buried in an elastic and homogenous half-space. The GNSS observations constrain well most of the model parameters but do not permit to discriminate between south- and north-dipping planes. The interferograms, produced from C-band ESA Sentinel 1 syntheticaperture radar data, give a clear preference to the north-dipping plane. The orientation of the GNSS vectors and the absence of InSAR fringes onshore Kos constrain the fault’s length. We also mapped surface motion away from thesatellite along the Turkish coast (from Bodrum towards east) which reached about 20 cm onshore islet Karaada. The best-fit model was obtained with a 37 deg. north-dipping normal fault, in agreement with the published moment tensor solutions. The slip vector is dominantly normal in a ESE-WNW direction with a component of left-lateral motion (5 deg.). The surface projection of the seismic fault outcrops in the Gökova ridge area, a well-developed bathymetric feature inside the western Gulf of Gökova (SE Aegean Sea). The seismic fault plane extends 14 km along strike by12.5 km wide. Our geodetic model is in agreement with relocated seismicity distribution (about 1160 events) from regional networks, which indicates an aftershock occurrence towards both ends of the rupture.

A seismic risk model on a building block scale is presented for the earthquake prone city of Aigion (W. Corinth Gulf) by combining deterministic seismic hazard with Risk-UE LM1 structural vulnerability, assessed per building, taking into account site conditions approximated by Horizontal-to-Vertical-Spectral-Ratios (HVSR) from ambient noise. The stochastic finite-fault method has been applied to simulate strong ground motion from two close earthquake scenarios, capable of occurring within the seismotectonic frame of the area: (a) a repetition of the 1995, June 15 (Mw=6.4) devastating earthquake and (b) a repetition of the 1861, December 26 earthquake of Mw=6.7 on the East Heliki Fault (EHF). The applied methodology provided comparable pattern with the real damage distribution of the 1995 earthquake, highlighting outlooks toward earthquake preparedness and riskmitigation purposes.

A deterministic seismic risk and monetary loss model is presented for the capital of Santorini volcanic Island, the town of Fira, on a building block scale. A local seismic source of M5.6 inferred from a recent volcano unrest in 2011–2012, detailed seismic vulnerability of 435 buildings and site conditions deduced from free-field ambient noise measurements were combined toward assessing the EMS-98 damage grade and its probability to occur. The seismic scenario yielded no damage or slight damage for 84{%} of the buildings, 16{%} of the constructions are expected to present moderate-to-heavy damage, while the economic loss amounts to 4 million euros. Although the model predicts low damage and direct economic loss, interaction with the touristic business activities might produce cascade side effects for the economy of the island and consequently Greece's GDP, an important part of which emanates from Santorini.

A major earthquake (Mwö=ö6.3) occurred on the 12th of June 2017 (12:28 GMT) offshore, south of the SE coast of Lesvos Island, at a depth of 13ökm, in an area characterized by normal faulting with an important strike-slip component in certain cases. Over 900 events of the sequence between 12 and 30 June 2017 were manually analyzed and located, employing an optimized local velocity model. Double-difference relocation revealed seven spatially separated groups of events, forming two linear branches, roughly aligned N130°E, compatible with the strike of known mapped faults along the southern coast of Lesvos Island. Spatiotemporal analysis indicated gradual migration of seismicity towards NW and SE from the margins of the main rupture, while a strong secondary sequence at a separate fault patch SE of the mainshock, oriented NW-SE, was triggered by the largest aftershock (Mwö=ö5.2) that occurred on 17 June. The focal mechanisms of the mainshock (φö=ö122°, δö=ö40° and λö=ö−83°) and of the major aftershocks were determined using regional moment tensor inversion. In most cases normal faulting was revealed with the fault plane oriented in a NW-SE direction, dipping SW, with the exception of the largest aftershock that was characterized by strike-slip faulting. Stress inversion revealed a complex stress field south of Lesvos, related both to normal, in an approximate E-W direction, and strike-slip faulting. All aftershocks outside the main rupture, where gradual seismicity migration was observed, are located within the positive lobes of static stress transfer determined by applying the Coulomb criterion for the mainshock. Stress loading on optimal faults under a strike-slip regime explains the occurrence of the largest aftershock and the seismicity that was triggered at the eastern patch of the rupture zone.

ABSTRACTWe exploit macroseismic observations and instrumental data aiming at explaining the effects of the 17th November 2015 Mw=6.5 earthquake, occurred beneath the southwestern peninsula of Lefkas Island (Ionian Sea) causing two casualties, major geo-environmental and slight-to-moderate structural effects. The spatial distribution of the structural damage of the local building stock is well correlated with the deformation pattern deduced from satellite geodesy, it appears though considerably low with respect to the ground deformation. Comparison with the previous strong earthquake on 14.8.2003 with Mw=6.2 occurred about 20 km to the north, shows that structural damage was significantly lower during the recent quake and also manifests good behaviour of the local buildings. This is partly explained by the characteristics of the ground motion and primarily explained by the unique concepts applied to the non-engineered buildings of Lefkas to resist ground motions.

This work describes the derivation of the tectonic stress from the inversion of focal mechanisms of double-couple earthquakes. The presented material is based, in large part, on several review papers, lecture notes and practices on the matter, developed by the authors during the last years.

A large amount of new and existing data was applied, aiming at delineating structural seismic risk in the earthquake prone modern city of Kalamata (SW Peloponnese) that was largely reconstructed after the devastating Mw=5.8 earthquake of September 13, 1986. Synthetic site-specifc ground motion parameters derived from the nearest known shallow hazardous seismogenic sources were combined with EMS-98 structural vulnerability estimates of the city’s building stock and four structural and economic loss models have been developed on a building-block scale. Assuming absence of non-linear, nearsource effects, the building stock of Kalamata is anticipated to present sufficient seismic behaviour, due to the large number of new and innovative constructions replacing the demolished ones after the 1986 earthquake.

Objectives: we present seismic and geodetic data analysis of the shallow, normal-faulting earthquake sequence offshore Lesvos (Aegean Sea, Greece) that was initiated by the June 12, 2017 M6.3 earthquake.Methods and Results: We use seismological data (relocated events and Moment Tensor solutions from NOA and KOERI catalogues) to identify the ESE-WNW striking seismic fault and to refine its geometry and kinematics using inversion techniques. Despite the large magnitude of the mainshock (M6.3), the surface deformation is not visible with InSAR because of the offshore occurrence of theearthquake. However, cm-size co-seismic horizontal offsets were recorded by the continuous GPS stations (of two private networks) operating at both Lesvos and Chios islands. In Sentinel co-seismic interferograms (C-band) we see no co-seismic displacements within ±0.3-0.5 fringe (±10mm). There are two local InSAR displacement patterns close to Plomari, possibly attributed to slope instabilities, which require further investigation. Lack of signal coherence was detected in the area of village Vrissa, that was heavily damaged by the earthquake.Conclusions: The spatial distribution of relocated events shows the activation of one fault with a total length of about 20 km, at depths 5-15 km. The fault-dip direction is not retrievable from GPS/InSAR but a south-dip is inferred from the aftershocks distribution and sea-bottom geomorphology. The absence of visible InSAR signal is consistent with the slip-model predictions, based on the GPS models.

During the last six years, our working group elaborated intense work on seismic risk assessment in several Greek cities, targeting site-specific models and allowing for tailor-made management actions in case of a crisis. In this paper we will present the main framework and the outcome of the applied methodologies on several case studies, indicating pros and cons, and highlighting future perspectives. Our approach includes: (a) Probabilistic and deterministic seismic hazard assessment based on comprehensiveTo this, new data concerning the location, geometry, and the seismic potential of faults, together with free-field ambient noise recordings have been collected through numerous field surveys; (b) Vulnerability assessment of elements at risk informed by newly created observed damage databases and in-situ observations; (c) Development of physical risk models including structural damage, and economic loss for several ground motion excitations scenarios. Future improvements that fall in with, and/or are beyond the current state-of-the-art, include: (a) and vulnerability assessment; (b) Socioeconomic impact analyses towards the mitigation of risk, enhancement of preparedness and resilience of the social and economic fabric, and (c) Applications for near real-time damage assessment by implementation of state-of-the-art opensourcesoftware (e.g. RASOR; OpenQuake

This study investigates fluid-driven seismicity in the Western Greece area. The region is characterized by the subduction of the Nubia (Africa) plate beneath the Aegean (Eurasia) plate (convergence rate of 40 mm/yr.) and is offset by the right-lateral active Cephalonia transform fault. The Ionian sedimentary basin is composed of thick Jurassic-Eocene carbonate and clastic sedimentary sequences underlain by Triassic evaporites that are thought to intrude through cataclastic zones generating diapiric structures. Due to the active tectonic and the abundance of fluids seeping in this region (with emphasis onshoreWestern Peloponnese) seismicity is often expressed as seismic swarms.To better constrain and investigate the evolution of (possible) fluid-driven seismic sequences we deployed from September 2016 to April 2017 a seismic network spanning 200 km from North to South and about 150 km from east to west. The network is composed of 14 temporary installations, while 9 permanent seismological stations are also considered in our analyses. We present results of accurate earthquake locations using a 1D velocity model developed using VELEST, highlighting regions where seismic activity is focused, and fault plane solutions derived from moment tensor inversion and first motion polarities. During the deployment we recorded several regional earthquakes (i.e. larger than M4.0) that allowed us to verify the effects of incoming seismic energy in this region.

The subject of this work is the investigation of the interaction between groundwater and seismic waves, resulting in liquefaction of the soil, a particularly dangerous phenomenon. Therefore, estimates of liquefaction potential can significantly contribute to the prevention of such effects and consequently to reduction of the seismic risk. The study area is Cephalonia Island, the most earthquake prone region of Europe. A dataset consisting of seismic ambient noise, accelerograms and datasheet from geotechnical boreholes, obtained after the 2014 earthquake crisis, has been analysed using a series of methodologies. Ambient noise analysis provided amplification functions, Vs30 models and synthetic time histories for numerous sites across the 2014 epicentral area. These were used for the seismic site characterization across the western part of the island and the estimation of the liquefaction potential in the coastal areas of Argostoli and Lixouri, where liquefaction phenomena were observed after the occurrence of the two strongest earthquakes in 2014. The results of the analyses are found to be compliant with the overall arrangement of the 2014 secondary earthquake effects, implying for strong site effects and interaction with the groundwater.

The site response during a strong earthquake event may be proven crucial for earthquake hazard assessment and risk mitigation. Two moderate magnitude earthquakes that occurred in early 2014 in Cephalonia produced the largest ground motion values ever recorded in Greece, highly exceeding the provisions of the effective seismic code implying for local effects. This motivated the investigation of site response in the epicentral area presented herein.

Earthquake hazards comprise any natural phenomenon associated withearthquakes. Earthquakes are known as the shaking of the Earth’s surface,producing significant impacts on both physical and urban environments withsevere socioeconomic aspects. Most of the earthquakes are generated at theboundaries of the lithospheric plates, which float over the mantle’s asthenosphere, converging or diverging. Friction caused by the plates interaction builds up stresses that, when released, produce ground faulting that radiates through the lithosphere producing complex seismic waves, which, in turn, can affect the near built environment. Although earthquakes mainly control the morphology of the Earth’s surface,they would unlikely be considered of major significance in the absence of theireffects on the anthropogenic environment, primary and secondary. Primaryearthquake hazards at a site regard the ground shaking due to the passage of theseismic waves (dynamic deformation) and/or the ground displacements (staticdeformation) in the vicinity of the causative fault. Secondary earthquake hazardsare the after-earthquake effects caused by the primary ones and may often bemore catastrophic. Such hazards are ground failures, fire, landslides, rock andsnow avalanches, liquefaction, flooding, tsunamis and seiche that have beenfrequently reported to follow the occurrence of strong earthquakes. The measureof earthquake hazards at a site mainly depends on the size and type of the seismic rupture, its distance from the site and the geological structure between the source and the site’s surface that may impact the seismic energy. Given that earthquake prediction is still infeasible, the major task in seismologicalresearch is the understanding of earthquake phenomena and their consequences on  the natural and anthropogenic environment, with the purpose of mitigating themby providing valid and timely information, to be used for effective earthquakeplanning and decision-making processes. Primary and secondary effects arerelated with vulnerability, which is defined as a set of prevailing or consequentialphysical and sociopolitical conditions that affect a community’s ability to mitigate,prepare for, or respond to an earthquake hazard (ADCP, 2003). Earthquakehazards, structural vulnerabilities and exposed values, when combined, yield aregion’s exposure to seismic risk.

Abstract We present a kinematic slip model from the inversion of 1 Hz GPS, strong motion, and interferometric synthetic aperture radar (InSAR) data for the 2015 Mw6.5 Lefkada, Greece, earthquake. We will show that most of the slip during this event is updip of the hypocenter (10.7 km depth) with substantial slip (>0.5 m) between 5 km depth and the surface. The peak slip is  1.6 m, and the inverted rake angles show predominantly strike-slip motion. Slip concentrates mostly to the south of the hypocenter, and the source time function indicates a total duration of  17 s with peak moment rate at  6 s. We will show that a 65° dipping geometry is the most plausible due to a lack of polarity reversals in the InSAR data and good agreement with Coulomb stress modeling, aftershock locations, and regional moment tensors. We also note that there was an  20 cm peak-to-peak tsunami observed at one tide gauge station 300 km away from the earthquake. We will discuss tsunami modeling results and study the possible source of the amplitude discrepancy between the modeled and the observed data at far-field tide gauges.

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 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.

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.

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.

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.

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.

Nowadays, Early Warning Systems (EWSs) are of great importance for urban seismic risk and emergency management. In this work, we describe the development and combination of a series of approaches for constructing a database of earthquake spatial effects towards creating a EWS for the Lefkada old town, situated in one of the most seismically active areas of the Mediterranean region. The geospatial information presented regards the earthquake damage probability at the target site and it is derived from seismic scenarios developed by combining seismic sources, vulnerability of buildings and site effects.Vulnerability was assessed empirically for individual buildings through a field survey.Site effects were determined using dense ambient noise HVSR measurements atselected points in Lefkada old town and available data from geotechnical boreholes.1D viscoelastic soil models were determined for each point by inverting the HVSRcurves using a Monte Carlo approach. Peak ground acceleration was assessed at each point using the point-source stochastic simulation scheme, by applying the siteamplification deduced from the 1D viscoelastic models. Seismic risk scenarios weredeveloped assuming two seismic sources (a) the earthquake on August 14th 2003 with M6.2 at a distance of 13 km from Lefkada old town and (b) a future nearest maximum credible earthquake with M7 at the same distance.The discrete damage probability was resolved by formulating a beta distribution of an average damage grade related to the vulnerability and the simulated PGA through empirical equations. The obtained models are found to be comparable with co-seismic observations during the 2003 earthquake and hence they are likely appropriate for preparing future emergency plans for the target site. An adaptable Arc-GIS automated procedure to map earthquake damage scenarios is currently being developed by implementing the above mentioned methods.

This work presents the current state of seismic vulnerability in Greece, the most seismically active region in Europe and the corresponding impacts of austerity measures imposed to the nation during the last five years. The analysis of physical risks and socio-economic conditions shows a very dangerous situation, which has to be promptly confronted, in terms of a revised and prioritized National reinforcement effort regarding pre-seismic preparedness and post-seismic interventions. The latter certainly requires funding, however it has to be coupled with restorative measures for the existing socio-political status embracing authorities, communities and individuals.

The present work constitutes the first part of a multi-parametric research for the representation of damage scenarios in Lefkada old town. The study area lies in the most seismically active zone of Greece and has suffered several devastating earthquakes. Most of its old buildings were built by local practices incorporating elements of earthquake resistance and have been designated as particular earthquake resistant constructions by the European Council Cultural Heritage Unit. The most recent earthquake of {\$}{\$}{\backslash}hbox {\{}M{\}}{\_}{\backslash}mathrm{\{}w{\}}=6.2{\$}{\$}Mw=6.2that occurred on 14 August 2003, located about 10 km from the town, caused moderate damage to its buildings and substantial geotechnical failures. Investigations on the coseismic effects yielded extensive literature information, which initially motivated our investigations. This paper deals with the empirical vulnerability assessment of the buildings in Lefkada old town based on basic structural characteristics such as the type and material of the structural system, the period of construction, the number of storeys, etc. Those characteristics, primarily available from the most recent available census were further exploited by an in-situ survey, during which all 1,420 buildings in the old town were inspected. Following, each building was indexed with an EMS-98 vulnerability class. Expert decisions on the damage scale due to the 14 August 2003 event were reassessed and converted into damage grades of EMS-98. The full data set was also analysed in ArcGIS producing detailed maps of the 14 August 2003 earthquake damage distribution by structural typology and vulnerability class in Lefkada old town.

Damage scenarios were developed for the Lefkada old town (LOT). LOT is the historical center of the capital of Lefkas Island, part of the Ionian Islands, one of the most seismically prone areas within the Mediterranean region that suffered numerous devastating earthquakes in the past. The most recent strong earthquake with Mw = 6.2 occurred on 14 August 2003 at a distance of about 13 km from LOT. A peak ground acceleration (PGA) equal to 0.42 g was recorded in LOT, one of the highest values ever recorded in Greece. Nevertheless, the 2003 event produced limited damage to the buildings of LOT, comprising traditional construction practices of architectural significance and a high seismic behaviour. Towards the development of damage scenarios the following tasks were performed: (a) buildings inventory and vulnerability indices determination using EMS-98 along with behaviour modification scores, (b) subsoil response functions and 1D visco-elastic models calculation using microtremors and (c) stochastic PGA simulation using site amplification deduced from the subsoil response functions. Two scenarios were developed considering the sources of the 2003 M6.2 earthquake and a future M7 event, located at the same fault. The discrete damage probability was resolved by formulating a beta distribution of an average damage grade related to the vulnerability index and the simulated PGA through empirical equations. The deduced models are comparable with the observed 2003 damage distribution, hence they are likely useful for preparing future emergency plans. In the aftermath, although further investigation is needed to explain outliers, the implementation of the followed methodology into an automated procedure for near real time shake and damage maps generation in case of a seismic crisis is highly recommended. The work herein, with proper adaptations, is potentially fairly applicable for other towns and regions in Europe.

We report cm-size dynamic displacements of continuous GPS stations onshore the island of Cephalonia, Ionian Sea, Greece, following the passage of seismic waves from two (2) shallow earthquakes on Jan 26, 2014 and Feb 3, 2014, respectively. First, we estimated the displacements from the high-rate GPS data collected at NOA station VLSM, near to the epicenters, by using state-of-art data processing strategies. The time series of displacements were analyzed both in time and frequency domains. From the dynamic analysis of 1Hz data it is shown that the second event was recorded at station VLSM with higher amplitudes on both horizontal components, despite its smaller (22 %) moment magnitude, possibly due to its shallower depth. The static field of deformation is characterized by cm-size permanent motion in opposing directions between stations KIPO (western Cephalonia) and VLSM (eastern Cephalonia), in agreement with the right-lateral kinematics of both ruptures. The 7.4 cm northward motion of station KIPO implies that the western peninsula of Cephalonia island (Paliki) belongs to a separate crustal block with respect to the rest of the island. The northward motion of KIPO also implies that the Cephalonia Transform Fault (CTF) did not rupture during the 2014 events, because KIPO is located at the hanging wall of CTF. It is possible that the amount of accumulated strain along CTF since 1983 (M=6.8) can be released by a seismic event of M6.5-6.7, at any time.

This study focuses on a series of small intraplate earthquakes that took place during May–August 2013 on the southwestern coast of the Corinth Rift (Central Greece), a few km southeast of Aigion city. The Corinth Rift is one of the most seismically active parts of the Mediterranean. We analyzed more than 1500 events with 0.4≤ML≤3.7, the major part of which was recorded by a dense local network. The seismicity is densely clustered in a volume of dimensions ∼4×2×6km3, aligned in a N110° direction and at depths ranging between 6 and 12km. Precisely relocated hypocenters and reliably constrained focal mechanisms indicate north dipping planar faults with an average dip of ∼60°. Stress inversion of focal mechanisms implies that the dominant local stress field is extensional in a N5° direction, in good agreement with geodetic observations. The swarm evolved in two phases, with a spatiotemporal migration of epicenters from the eastern toward the western part of the rupture zone, while slip distribution appears homogeneous over the eastern part and strongly inhomogeneous in the western part. These two phases also produced different results in scaling relations such as the Gutenberg–Richter law, the Modified Omori Formula and the Epidemic Type of Aftershock Sequence model. Similar results from other studies have been reported and correlated with a fluid driven mechanism, however further research is required to strengthen this hypothesis for the purposes of this study.

A significant earthquake sequence was initiated on 26 January 2014 at the western part of the Kefallinia Island. The study area is located in the Ionian Sea (W. Greece) at the northwestern end of the Hellenic Arc – Trench, in a region dominated by the Kefallinia - Lefkada transform fault, which exhibits dextral strike–slip motion at a rate of 2–3 cm year−1During the historical period, until 1900, 13 earthquakes with magnitude Μ≥6.0, have been reported in the Kefallinia region. The strongest event, of magnitude 7.4 and intensity X at Lixouri, occurred on 4 February 1867 (Papazachos and Papazachou, 2003; Stucchi et al., 2012). Major destructions were reported at the villages of the Paliki peninsula, while in Lixouri only two houses did not collapse. Ground ruptures were observed, as well as a tsunami of small height. Rock falls and liquefactions also occurred. In the Paliki peninsula 2612 houses collapsed, while only 4 in Argostoli, the capital and major town of the Kefallinia Island. Since 1900, 11 earthquakes with magnitude Μs≥6.0 occurred (Makropoulos et al., 2012) in the region. Five of them took place in 1953, four of which during August. The largest event had a magnitude equal to 7.3 and maximum intensity X+ in Argostoli. This earthquake was preceded by two strong events (Ms=6.1 and 6.8). The Ionian islands of Kefallinia, Zakynthos and Ithaca suffered very severe damages. Among the 33300 houses, 27659 collapsed. The highest intensities (IX-X) were observed, among other locations, at Argostoli, Lixouri and Valsamata. Thirty years later, on 17 January 1983, an event with magnitude Ms=7.0 occurred approximately 30 km SW of Lixouri, causing moderate damage. The most recent moderate event (Mw=5.6) occurred on 25 March 2007, 5 km NE of Mirtos Bay. (Kahle et al., 1996; Cocard et al., 1999). This region is situated between the Hellenic subduction zone to the south and the Apulia - Eurasian collision zone to the north. Focal mechanisms reveal right-lateral strike-slip motion (Anderson and Jackson, 1987; Jackson and McKenzie, 1988), coherent with geodetic data, according to which the slip motion has a NNE–SSW direction (Cocard et al., 1999; Jenny et al., 2004).On Sunday 26 January 2014 (13:55 GMT) a strong shallow earthquake of magnitude Mw=6.1 occurred in the study area. The epicenter is located about 2 km NE of Lixouri. It is worth noting that no significant earthquake sequence was recorded at the Paliki Penisula during the last decades. The main shock and the aftershock sequence were recorded by seismographs of the Hellenic Unified Seismological Network (HUSN), which involves the Seismological Laboratories of the Athens and  Patras Universities, the Department of Geophysics of the Thessaloniki University and the Geodynamic Institute of the National Observatory of Athens (GI-NOA).Ground motion of the 26-1-2014 mainshock (Mw=6.1) was recorded by three permanent accelerographs located in Argostoli, Lixouri and Vassilikiades (ITSAK-EPPO, GI-NOA) with the response spectra in Lixouri indicating high horizontal acceleration. Moreover, the vertical component exhibited high spectral acceleration at a lower period when compared to the horizontal ones. Similar pattern is observed for the next strong event, which occurred on February 3, 2014 (Mw=5.9). A temporary accelerograph installed complementary to the permanent stations by GI-NOA in Chavriata, south of Lixouri, recorded an effective acceleration of 1g for the latter event, surprisingly exceeding the Greek Seismic Code provisions (0.36 g), being the highest recorded in Greece.The aftershock sequence was intense, while five hours after the mainshock, an aftershock of magnitude Μw=5.2 occurred. This sequence continued for a week with more than 30 events having magnitude greater than 4.0, till the occurrence of a strong earthquake of magnitude Μw=5.9. Its epicenter was located at the northwestern part of the Paliki peninsula. The earthquake sequence consists of more than 2000 events, the focal depths of which range mainly between 4 and 18 km. The aftershocks spatial distribution indicates that the activated seismogenic area is about 30 km length, in a NNE direction, located onshore in Paliki peninsula. At least three clusters can be distinguished. It is bounded to the south by the Vardiani islet and to the north by Myrto’s bay.The source parameters determination of the two strongest events were determined using body-wave modeling and teleseismic recordings. Synthetic waves are calculated by the trial-and-error method to determine the focal mechanism, the focal depth, and the seismic moment for a single trapezoidal source time function (Papadimitriou et al., 2006). Focal mechanisms of the strongest aftershocks have also been determined using the moment tensor inversion method developed by the Seismological Laboratory of the University of Athens (Papadimitriou et al., 2012). The data used are digital waveforms, recorded in regional distances by stations of HUSN. The observed seismograms were band-pass filtered between 0.02 Hz to 0.08 Hz. Following, Green Functions were calculated using the method proposed by Bouchon (1981). The inversion method revealed strike-slip focal mechanisms, in agreement with the fault plane solutions of the two main shocks. The results point out a dextral strike-slip rupture, oriented in a NNE-SSW direction. Taking into account both the aftershock spatial distribution and the focal mechanisms, it is concluded that the activated area does not coincide with the regional catalogue seismicity that is attributed to the Kefallinia - Lefkada transform fault, located offshore. Hence, activation of a sub-parallel major fault can be considered, compatible with the active tectonics of the region, which is crucial for its seismic hazard.

On May 21st , 2013, a large series of small earthquakes initiated a cluster formation, few km to the southeast of the city of Aigion, on the southwestern coast of the Gulf of Corinth in Central Greece. Over the next ten days more than 250 shocks with M<3.4 had been reported and on May 31st a M=3.7 earthquake was strongly felt and was accompanied by more than 100 smaller shocks within a 24 hour period. On July 13th-14th another outburst was reported with the occurrence of four M=3.0-3.5 events, followed by more than 250 earthquakes for the next three days. Thereafter, the activity diminished and terminated in the beginning of August. This unexpected phenomenon alarmed the local citizens because the seismic history of the area involves the occurrence of the great earthquake of 373 B.C, which extinguished the ancient city of Heliki, as described in great detail by Aristotelis in 330 B.C. The recent seismic history of the region has indicated that the Gulf of Corinth produces significantly high strain rates and it is ranked as the 'fastest’ continental rifts in the world and the most seismically active part of the Mediterranean. After the most recent catastrophic earthquake in 1995 with Ms=6.2 to the north of Aigion city, several seismological and geophysical networks have investigated the area and these have provided valuable scientific information concerning the regional seismotectonic regime. Shortly after the initiation of the May 21st, 2013 activity in Aigion, a local network of 10 portable seismographic stations was installed in the area, by the Institute of Geodynamics of the National Observatory of Athens and the Seismological Laboratory of the National Kapodistrian University of Athens. This network has been transmitting real-time data to the Hellenic Unified Seismological Network and recorded about 1000 events significantly improving the detectability of local earthquakes and the associated seismic hazard evaluation. In this study we investigate the dynamics and spatio-temporal characteristics of the sequence.For this purpose we performed relocation of the whole sequence using catalogue and waveform data and an optimized velocity structure, which improved the initial hypocentral solutions by the order of amagnitude. A large number of focal mechanisms was computed using P-wave first motion polarities of the local recordings, implying for shallow E-W normal faulting, compatible with regional tectonics. Furthermore, we employed a scheme involving the temporal frequency-magnitude and stress field distribution aiming to interpret the causative and triggering mechanism of the activity.

Lefkada Island is situated off the west coast of the Greek mainland and belongs to the complexof the Ionian Islands, one of the most seismically prone areas within the SE Mediterranean region,dominated by the right lateral Cephalonia Transform Fault Zone. As it is reported from historical andinstrumental catalogues the study area has suffered numerous devastating local earthquakes withM>6.0. The most recent strong earthquake occurred on 14 August 2003, having M=6.2, at a distanceof only 10 km from the town of Lefkas where a peak ground acceleration of 0.42g was recorded, beingone of the largest observed in Greece during the last decades. Although the earthquake producedlimited damage to the building stock, it likely induced damages of geotechnical character, associatedwith extensive liquefaction mainly in the waterfront of the town. Coseismic failure observationsprovided an expansive database which tempted us and triggered a multitasking project toward lossassessment in the Lefkada Old Town (LOT), comprising traditional construction practices ofarchitectural significance and high seismic behaviour as a rule.The project employs several modules which were performed successively during the last years:(A) Macroscopic analysis of the buildings stock in LOT by conducting a comprehensive in-situinventory of the buildings; (B) Vulnerability classification of the building stock using EMS98; (C)Ground Motion Parameters (GMP) determination for regional hazard assessment; (D) Site effectsresulting from a detailed ambient noise study conducted in LOT; (E) Analysis of availablegeotechnical information and in-situ measurements of the local soil properties; (F) Employment ofdamage distributions during the recent 2003 earthquake; (G) Development of an ARC-GIS platform toinclude and allow the process of the massive data collected.In this paper we present a first attempt to synthesize the above modules in order to investigatesoil-structure interactions in LOT, assuming a linear response for both. By using various seismicsources whose characteristics are inferred by the active tectonics and the probabilistic hazardassessment of the study area, strong ground motion has been simulated both stochastically anddeterministically for hard bedrock conditions. GMPs were constrained beneath the foundations of thebuildings by convolving the simulated ground motion with the soil transfer functions deduced frommicrotremors. According to this, for each scenario a damage potential has been assigned at eachbuilding. The obtained patterns were proven to be fairly comparable with the damage distribution dueto the 2003 event, hence constituting a provocative motivation for further investigation and otherapplications.

This work is part of a multi-parametric research towards representation of damage scenarios in theLefkada old town. The study area lies in the most seismically active zone of the Greek territory. Mostof its buildings were built with local practices and have been designated by the European CouncilCultural Heritage Unit as representative earthquake resistant constructions. The August 14th, 2003(Mw=6.2) local earthquake produced several damage in the old town of Lefkada, with aninhomogeneous spatial distribution. In this paper we investigate the correlation of the observeddamage pattern with soil characteristics using data collected during an ambient noise survey conductedin 2007. Those were analyzed following Nakamura's HVSR methodology and soil response wasapproximated by the dominant frequencies and quasi-amplification factors of the resulted HVSRcurves. The latter were further inverted using a Monte-Carlo approach and best-fitting site specificgeotechnical models were determined. The obtained results are reasonably consistent with boreholetest data and show a remarkably good correlation with the 2003 damage distribution.

On 10 April 2007, three moderate earthquakes with Mw=4.9–5.1 occurred in the vicinity of Trichonis Lake (W. Greece). A local network composed of 12 three-component digital seismographs was installed in the epicentral area and recorded more than 1600 events. The double-difference algorithm HYPODD, incorporating both catalog and waveform cross-correlation differential travel-time data, was applied for the successful relocation of 1490 earthquakes. The latter led to the distinction of a main NW-SE trending and NE-dipping zone, as well as of three neighboring faults; a conjugate NW-SE striking and SW-dipping marginal fault mapped along the northeastern flanks of the lake; a E-W trending and south-dipping low-angle normal fault, possibly related to the major Agrinio Fault Zone (AFZ), parallel to the northern bank of the lake; a NE-SW striking and NW-dipping normal fault, likely related to a segment of the active Evinos fault, located south of the lake. Calculation of the Coulomb stress induced by the combination of the 1975 Mw=6.0 event and the three largest events of 10 April 2007 on the inferred structures, reveals that most of the seismicity lies within the “stress-loaded” region, except for the westernmost activity, which probably belongs to the deep part of the AFZ. A total of 178 reliable focal mechanisms were determined by regional and local body-wave modeling (5 largest events) and P-wave first motion polarity data. The types of the obtained focal mechanisms are predominantly normal and strike-slip, however, numerous earthquakes were found to exhibit reverse faulting. Inversion of focal mechanism data showed that the prevailing principal horizontal component σ3 is quite homogeneous throughout the activated area with a roughly NW-SE trend, parallel to the strike of the Hellenides. On the contrary, the compressional field σ1 appears in two patterns: NE-SW trending onshore and NW-SE trending beneath the lake. This apparent rotation of σ1 by 90° reveals a complex system enclosed by the suggested NW-SE trending antithetic faults in depths between 7 and 9km. The calculated stress ratios beneath the lake imply that vertical forces are close to the overburden pressure. The overall inferred stress pattern is rather linked to topographic variations, locally imposing increase or decrease of the vertical forces. The presence of the water in the lake possibly plays an additional important role, penetrating through the bedrock, reducing the friction coefficient, while the pore pressure and, consequently, the effective stress increase. Thus, shearing along mature fractures is enhanced, likely yielding the observed diversity.

In this paper, we present a detailed study of a shallow seismic swarm which took place in the area of Oichalia (SW Peloponnesus), between August and December 2011. The seismic crisis started on 14/8/2011 with an Mw=4.8 earthquake and was followed by more than 1600 events, several of which having magnitude over 4.0. The activity was recorded by local temporary and regional permanent seismic stations. Thousands of records were collected and routinely analyzed. P- and S-wave arrival times were manually picked and incorporated in the HYPOINVERSE algorithm together with a new optimum local velocity model. Hypocentral solutions were improved by applying a double-difference method. Focal mechanisms show that the activated fault zone is dominated by dip-slip normal faulting, trending NNW–SSE, with the average T-axes orientation being N70°E, consistent with regional tectonics. We have investigated towards stress triggering and fluid diffusion, by employing Coulomb stress transfer, spatio-temporal and Frequency–Magnitude Distribution (FMD) analyses. The negligible Coulomb stress transfer and seismicity rate changes that were calculated imply for a stress deficit in the broader study area, hence an external triggering mechanism is required to justify the observed pattern. The b-values increase towards the SSE, compatible with the similarly directed migration of seismicity, showed that the Oichalia swarm could possibly be adapted to an Epidemic Type Aftershock Sequence model (ETAS). Fluid diffusion is reflected in the spatio-temporal hypocenter migration. Clustering analysis, combined with the temporal distribution of b-values, has shown that the swarm evolved in three major phases, the first two being initiated by major events, which were probably triggered externally due to fluid injection that brought the seismogenic volume into a critical state, likely followed by afterslip. The last phase signified a relaxation period, with dispersed seismicity throughout the area and the b-values gently diminishing towards unity.

The seismic history of the centre of Athens may be revealed through the response of its classical andneo-classical columns to ambient noise and earthquake shaking. Detailed ambient vibration surveys in two casesare presented: a) the two choragic columns on the south slope of the Acropolis, above the Monument ofThrasyllos, constructed in the late classical-early Hellenistic era (3rd–1st century B.C.), with an original designand a high constructive quality (13 April – 10 May 2011) b) the statue of Apollo (mid-19th century), on the rightside of the Academy of Athens building prostyle, mounted on a column in the Ionian rhythm (5-13 March 2008).In the first (Acropolis) case, ambient noise measurements were performed with seven digital 3-componentseismographs at the top and the base of each column, as well as at three nearby reference sites. In addition,forced vibration tests at the top of each column were also conducted. In the second (Academy) case, fiveinstruments of the same type were installed at the base of the column, the base of the statue, with reference sitesat the two corners of the Academy building and the garden at the back side of the building. For both cases, the response spectra and amplitude ratios were computed, providing information on the soil-column interaction, as well as the characteristic frequencies of spectral ratios peaks.

The purpose of this paper is to assess the vulnerability to ground shaking of the building stock in the old town of Lefkada Island (Ionian Sea, W. Greece). The study area lies in the most seismically active zone of Greece region. Most of its buildings were built with local practices and have been designated by the European Council Cultural Heritage Unit as representative earthquake resistant constructions. Within the context of this research we conducted an in-situ survey, of all buildings in the old town. In addition, the 2001 buildings census catalogue elaborated by the National Statistical Service of Greece was employed, as well as the damage inspection data following the 2003 earthquake. The collected data, after a detailed processing, were projected as they would have been prior to the August, 14, 2003, Mw=6.2 Lefkada earthquake. Each building was indexed by an EMS-98 vulnerability class. All results were combined in an ArcGIS scheme in order to compute the lateral vulnerability distribution and to compare it with the 14/8/2003 earthquake effects.

Historical buildings are important structures and their preservation and restoration is a vital issue worldwide. A crucial step before interventions is the definition of potential hazards and the monument’s vulnerability estimation. The Kapnikarea chapel is one of the most important and popular Byzantine monuments in Athens and dates back to the 11th century. In 1994, construction of the Athens underground Metro system began, with the tunnels passing underneath Kapnikarea foundations. During excavations, sounds of the approaching underground activities (heavy drilling and hydraulic hammer equipment) were heard in the interior of the chapel, and several failures were observed inside the church. Additional reasons reduced the structure’s rigidity are deterioration in time and past severe earthquakes. Towards the restoration planning of the monument, the University of Athens together with the Hellenic Ministry of Culture and Tourism, assigned to our research group the task to investigate the fundamental frequencies of the monument and of its soil foundation in order to determine resonance phenomena capable of compromising building stability during an earthquake. For this purpose, we conducted a microtremor survey. Ambient noise measurements were taken for 87 points located both on the ground and the chapel. Using the HVSR technique we determined the response of the ground, the monument’s predominant frequency and the spatial variations of the peak frequencies on the monument. Based on the experimental observations we discuss the possibility that differentiations are due to the structural members’ particularity and/or health.

The highest deformation rate along the Africa/Eurasia convergence zone is welldocumented in the Aegean area, being >4 cm/yr. However, it is still under question whethercontinental deformation is distributed along major faults which extend through the wholelithosphere or over large areas. Furthermore, our knowledge concerning the implication oflithosphere-asthenosphere coupling in lithospheric plates driving forces is poor. Thesequestions can not easily be answered as most of the available information is mainly located ator close to the surface (geodesy, tectonics, seismicity). The high rates and type of surfacecontinental deformation within the Aegean constitute this region particularly interesting in thisperspective.This work is towards contributing to the better knowledge of the physical properties ofthe Aegean lithosphere by introducing experimental elastic and anelastic parameters inferredfrom long period Rayleigh wave. For this scope path-average phase velocities and attenuationcoefficients of fundamental Rayleigh wave crossing the Aegean were extracted over theperiod range 10-100 s. The wavetrains were recorded at the temporary broadband stationsinstalled some years ago in the Aegean region within the framework of a large scaleexperiment (SEISFAULTGREECE project).

This study presents results of ambient noise measurements carried out in 78locations in the town of Lefkada. The horizontal-to-vertical spectral ratios of ambient noise were used to approximate the fundamental resonance frequencies of the subsurface and their associated amplitudes. Summarizing the experiences of different authors with respect to ambient vibration processing, we selected transient free time windows for further analysis. Additionally, we calculated the site responses with respect to the reference site and compared the results with those obtained from the H/V technique. The fundamental frequency and the corresponding amplification factor were calculated for each site. Under the assumption that the H/V spectral ratios of ambient noise coincide with the amplification levels at the dominant frequency of the site response functions, the fundamental frequencies (f0) and amplification factors (A0) were compiled on ARC-INFO GIS software and corresponding maps were developed.

This paper presents a new shear velocity and attenuation model for the lower crust and litho-sphere of the Aegean region, obtained by inversion of broadband surface-wave phase veloci-ties and attenuation coefficients. We have two main motivations for conducting this study. First, knowledge of the regional structure of the Aegean lithosphere is fundamental for understanding the tectonic framework and mantle dynamics, posing constraints on possible models of deformation and evolution. Second, the exponential dependence of Q with temperature implies that attenuation tomography could explain better hot regions (high attenuation) than elastic tomography. Furthermore, elastic velocity is highly influenced by the constitution of the medium. In case of strong lateral Q variations, elastic parameters also vary. Hence, it is important to combine results of elastic and anelastic tomography. Apparently, the high rates of deformation in the Aegean constitute this region particularly interesting in this perspective.

Anelasticity of the Earth crucially affects the propagation of seismic waves especially, in the long period range. However, even though the elastic properties of the Aegean deep lithosphère and upper mantle have been thoroughly investigated, their quantitative anelastic properties that influence the long period wavefield are still largely unknown. This work is towards contributing to the better knowledge of the deep structure of the Aegean by introducing experimental anelastic parameters via the study of long period Rayleigh waves attenuation. For this scope, fundamental mode attenuation coefficients (γ%) have been obtained for different two-station great-circle paths across the Aegean. The data used were provided by a broadband array installed in the area for 6 months in 1997. More than 1100 seismograms were analyzed in the 10-100 s range to obtain 17 sets of path average γR(T) functions. The attenuation coefficients are in the range 2.5*10~3 — 0.15 x 10' km' and correlate sufficiently with both experimental measurements in active tectonic regions elsewhere and synthetics generated with the use of an attenuation reference model inferred from other sources. By applying a stochastic uncoupled causal inversion method an average joint Qß'1 and shear velocity model representative of the under study area was obtained. Furthermore, path average JR(T) functions were combined in a continuous regionalization tomographic scheme to obtain local yR(T) and tomograms were constructed in the range 10-60 s. The most prominent feature in the tomograms is a high attenuation region in the central and north Aegean. This region is located south of the North Anatolian Trough and correlates well with a low shear velocity zone inferred from surface wave phase velocities. Moreover, it is associated with observed intense extensional deformation rates, mantle olivine anisotropy, recent volcanism and high heat flow.

During November 2004 – June 2005 a digital seismological network was deployed in the eastern part of central Greek mainland, in an area seismically active in the 20th century, particularly in the decade of fifties. The strongest earthquake (M=7.0) occurred in 1954, while the last strong one in 1980 (M=6.5). In total 18 Reftek digital loggers (both 72A–07 and R–130) were installed assembled with fifteen guralp CMG40T broadband and three Le_1Hz seismometers. The average spacing between stations was of the order of 20 km to ensure earthquake depth accuracy. Local earthquakes with P– and S– arrivals at four or more stations were located using HYPOINVERSE computer program. Data analysis using the Double Difference technique did not changeconsiderably the spatial distribution of the earthquake foci. The best–recorded earthquakes were used to define a reasonable crustal structure. Lateral variations of the crustal model taken into account, calculating time delays for each station. By this way, earthquakes inside the network or close to its boundaries were located with high accuracy in both the epicenter and focal depth. In addition, focal mechanisms of earthquakes with proper azimuthal coverage were computed. Seismicity covers most of the area and is distributed mainly in clusters along active structures. A magnitude M=3.9 earthquake, was the largest local one recorded by this network (5 December 2004, 17:58 UTC), close to the focal area of the 1980 strong earthquake. Several cross sectionsstriking normal to the trend of the clusters of the epicenters reveal the geometry of the active structures as well as the width of the seismogenic layer. Most of the focal mechanisms exhibit normal faulting and were used along with the microseismicity foci in the cross sections for the definition of the properties of the faults that activated during the experiment.

{The 3-D structure of the lithosphere beneath the Aegean Sea is investigated through surface wave dispersion analysis. Rayleigh and Love waves recorded by 12 broad-band stations installed for a duration of 6 months in the Aegean region are processed through array analysis and Wiener filtering. Data from three GEOFON stations in the area of Crete were also used. The resulting two-station phase velocities are used to determine lateral variations of Rayleigh wave phase velocities between periods of 20 and 100 s by a 2-D ray tomography method. The obtained phase velocities are inverted to calculate variation of S-wave velocity with depth using a combination of linearized inversion and a Monte Carlo based non-linear inversion.The absolute S-wave velocity is resolved to a depth of approximately 200 km. A high-velocity anomaly of 3 per cent is observed in the southern Aegean attributed to the Hellenic subduction. In the northern part of the Aegean, in the prolongation of the North Anatolian Fault which is influenced by strong extensional movements, we found low absolute S-wave velocities at 50–100 km depth. This supports a model of a distributed deformation of the upper mantle in the area. Separate Rayleigh and Love wave phase velocity inversions along common profiles reveal a strong Love–Rayleigh discrepancy in the northern Aegean down to at least 150 km depth, i.e. most probably including the top of the asthenosphere.}

Fundamental mode Rayleigh waves generated by 380 teleseismic events were analyzed over the period range 10-100 s, in order to study the structure of the lithosphere and upper mantle of the Aegean region. Using the two-station method, 255 reliable phase velocity dispersion curves were calculated over 35 profiles and further inverted to obtain a new model of S-wave velocity with depth. S-wave velocities are resolved to a depth of 180 km. Important features are defined, such as a not completely amphitheatric geometry for the western (≈25° dipping angle) and eastern segments (≈35° dipping angle) of the subducted slab. In north Aegean, high velocities associate with the North Aegean Trough, which westernmost tip correlates with a high velocity anomaly in eastern continental Greece. This zone of high velocity contrast is extended in depth, dips southwards with an angle ≈350 and intersects with the subducted slab at an area where the direction of major tectonic axes changes from ENE-WSW to NNW-SSE towards the continental massif. In Central and North Aegean, where back arc extension and crustal thinning occur, the predominant low velocities observed could be interpreted by upper mantle high thermal flow and partial melting.

On 7 September 1999 at 11:56 GMT a destructive earthquake (Mw = 6.0) occurred close to Athens (Greece). The rupture process is examined using data from the Cornet local permanent network, as well as teleseismic recordings. Data recorded by a temporary seismological network were analyzed to study the aftershock sequence. The mainshock was relocated at 38.105°N, 23.565°E, about 20 km northwest of Athens. Four foreshocks were also relocated close to the mainshock. The modeling of teleseismic P and SH waves provides a well-constrained focal mechanism of the mainshock (strike = 105°, dip = 55° and rake = -80°) at a depth of 8 km and a seismic moment M0 = 1.01025 dyn·cm. The obtained fault plane solution represents normal faulting indicating an almost north-south extension. More than 3500 aftershocks were located, 1813 of which present RMS < 0.1 s and ERH, ERZ < 1.0 km. Two main clusters were distinguished, while the depth distribution is concentrated between 2 and 11 km. Over 1000 fault plane solutions of aftershocks were constrained, the majority of which also correspond to N–S extension. No surface breaks were observed but the fault plane solution of the mainshock is in agreement with the tectonics of the area and with the focal mechanisms obtained by aftershocks. The hypocenter of the mainshock is located on the deep western edge of the fault plane. The relocated epicenter coincides with the fringe that represents the highest deformation observed on the differential interferometric image. The calculated source duration is 5 sec, while the estimated dimensions of the fault are 15 km length and 10 km width. The source process is characterized by unilateral eastward rupture propagation, towards the city of Athens. An evident stop phase observed in the recordings of the Cornet local stations is interpreted as a barrier caused by the Aegaleo Mountain.

A detailed analysis of the aftershock sequence of the September 7, 1999 Athens earthquake was performed in order to define the fault planes activated during this sequence and study the tectonic regime of the area. Calculated fault plane solutions were verified by the composite solutions and the application of the principal parameters method. The combined results indicate a uniform tectonic status in the western part of the aftershock area, with normal faulting of WNW-ESE trend and an average dip of 60Ί and a more complex one in the eastern part, where the azimuths of the activated fault planes vary and a transverse antithetic fault is also active. This variation could possibly imply a variation of the local stress field.

Seismic anisotropy, deduced from SKS splitting measured at 25 stations installed in the Aegean, does not show a homogeneous pattern. It is not restricted to the North Anatolian Fault but is distributed over a region several hundreds kilometers wide. Little anisotropy is observed in continental Greece or along the Hellenic arc; however, significant anisotropy is observed in the north Aegean Sea. Large values of delay times suggest that anisotropy is due to a long path within the upper mantle and to strong intrinsic anisotropy. Our results, both in fast polarization directions and in values of delay time, do not support the idea that anisotropy is associated with inherited tectonic fabric nor are they consistent with the present-day Aegean motion relative to an absolute frame. In contrast, the direction of fast polarization and the magnitude of delay times correlate well with the present-day strain rate observed at the surface deduced from both geodetic measurements and seismicity. This anisotropy is not horizontally restricted to major surface faults but is spread over a wide region.

{During the summer of 1993, a network of seismological stations was installed over a period of 7 weeks around the eastern Gulf of Corinth where a sequence of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal faulting with the active fault plane dipping at about 45° for both faults. The aftershocks of the 1981 earthquake sequence recorded by King et al. (1985) were processed again and show similar results. In contrast, the observations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 (Rigo et al.), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes (Hatzfeld et al. 1996; Bernard et al. 1997) show seismicity dipping at a very low angle (about 15°) northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30°. We suggest that the 8–12 km deep seismicity in the west is probably related to the seismic—aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal mechanisms between east and west of the Gulf could be related to the difference in the recent extension rate between the western Gulf of Corinth and the eastern Gulf of Corinth, which rotated the faults dipping originally at 45° (as in the east of the Gulf) to 30° (as in the west of the Gulf).}

We report here the results of a tomographic lithospheric study in the area of the Corinth and Evvia rifts (Greece), designed to constrain the mechanism of continental extension. Sixty seismological stations were deployed in the area for a period of 6 months, and 177 teleseismic events were recorded by more than five stations and gave more than 2000 travel time residuals (P and PKP phases), which were inverted to image the velocity structure down to 200 km depth. We use both a linear and a nonlinear method to invert the data set. The main result is a long-wavelength positive velocity anomaly located in the upper mantle, which is interpreted as the subducted African lithosphere. The subducted lithosphere is well defined from ∼7O km depth down to 200 km. From synthetic tests as well as from the amplitude of the anomaly (more than +7%) we conclude that the subduction continues below 200 km. In addition, a second positive velocity anomaly of about +4% from the surface down to 40 km depth, located north of the Gulf of Corinth, has been found. This is interpreted as the result of a crustal thinning of several kilometers (∼5 km), shifted to the north from the Gulf of Corinth and trending obliquily NW-SE. We suggest that this crustal thinning is mainly related to the Miocene widespread extension in the Aegean and that the Quaternary Corinth rift initiated where the crust was already thinned. The different styles of deformation of the eastern and western part of the rift are consistent with this interpretation. No clear velocity anomaly can be related to the Evvia rift.

We present the results of a multidisciplinary study of the Ms = 6.2, 1995, June 15, Aigion earthquake (Gulf of Corinth, Greece). In order to constrain the rupture geometry, we used all available data from seismology (local, regional and teleseismic records of the mainshock and of aftershocks), geodesy (GPS and SAR interferometry), and tectonics. Part of these data were obtained during a postseismic field study consisting of the surveying of 24 GPS points, the temporary installation of 20 digital seismometers, and a detailed field investigation for surface fault break. The Aigion fault was the only fault onland which showed detectable breaks (< 4 cm). We relocated the mainshock hypocenter at 10 km in depth, 38 ° 21.7 ′ N, 22 ° 12.0 ′ E, about 15 km NNE to the damaged city of Aigion. The modeling of teleseismic P and SH waves provides a seismic moment Mo = 3.4 1018 N.m, a well constrained focal mechanism (strike 277 °, dip 33 °, rake − 77°), at a centroidal depth of 7.2 km, consistent with the NEIC and the revised Harvard determinations. It thus involved almost pure normal faulting in agreement with the tectonics of the Gulf. The horizontal GPS displacements corrected for the opening of the gulf (1.5 cm/year) show a well-resolved 7 cm northward motion above the hypocenter, which eliminates the possibility of a steep, south-dipping fault plane. Fitting the S-wave polarization at SERG, 10 km from the epicenter, with a 33° northward dipping plane implies a hypocentral depth greater than 10 km. The north dipping fault plane provides a poor fit to the GPS data at the southern points when a homogeneous elastic half-space is considered: the best fit geodetic model is obtained for a fault shallower by 2 km, assuming the same dip. We show with a two-dimensional model that this depth difference is probably due to the distorting effect of the shallow, low-rigidity sediments of the gulf and of its edges. The best-fit fault model, with dimensions 9 km E–W and 15 km along dip, and a 0.87 m uniform slip, fits InSAR data covering the time of the earthquake. The fault is located about 10 km east-northeast to the Aigion fault, whose surface breaks thus appears as secondary features. The rupture lasted 4 to 5 s, propagating southward and upward on a fault probably outcropping offshore, near the southern edge of the gulf. In the shallowest 4 km, the slip – if any – has not exceeded about 30 cm. This geometry implies a large directivity effect in Aigion, in agreement with the accelerogram aig which shows a short duration (2 s) and a large amplitude (0.5 g) of the direct S acceleration. This unusual low-angle normal faulting may have been favoured by a low-friction, high pore pressure fault zone, or by a rotation of the stress directions due to the possible dip towards the south of the brittle-ductile transition zone. This fault cannot be responsible for the long term topography of the rift, which is controlled by larger normal faults with larger dip angles, implying either a seldom, or a more recently started activity of such low angle faults in the central part of the rift.

{The Kozani earthquake (Ms = 6.6) of 13 May 1995 is the strongest event of the decade in Greece and occurred in a region of low seismic activity. Using regional data and the strong-motion record at the Kozani station, we relocate the mainshock at 40.183° N and 21.660° E, beneath the Vourinos massif at a depth of 14.2 km. We also compute a focal mechanism by body-waveform modeling at teleseismic distance, which confirms a normal mechanism. The most likely plane strikes 240° ± 1° N and dips 40° ± 1° N with a centroid depth of 11 ± 1 km. Modeling of the strong-motion record at Kozani confirms that nucleation started at the eastern termination of the bottom of the fault.Six days after the mainshock, we installed a network of 40 portable seismological stations for one week around the epicentral region. Several thousand aftershocks were recorded, among which we locate 622 with a precision better than 1 km. We compute 181 focal mechanisms that mostly show normal faulting. The aftershock seismicity is restricted between 5 and 15 km depth and defines a plane dipping north at an angle of about 35°, consistent with the mainshock mechanism. Seismic activity with the same pattern of normal fault mechanisms is also seen on an antithetic fault connected to the main one at 12 km depth, which cuts the ground surface north of the Vourinos ophiolite massif in the Siatista valley. These results suggest two possibilities for the active fault plane; either it is the Deskati fault that is flat and dips with a constant angle, and therefore the surface breaks are secondary features, or, more likely, it is the Paleohori fault that is new, of listric shape, and located ahead of the Deskati fault, which was not active during the earthquake.}

{We present the results of a dense seismological experiment in the western part of the Gulf of Corinth (Psathopyrgos-Aigion area), one of the most active rifts in the Aegean region for which we have precise tectonic information. The network included 51 digital stations that operated during July and August 1991, covering a surface of 40 times 40 km2. Among the 5000 recorded events with ML ranging between 1.0 and 3.0, we precisely located 774 events. We obtained 148 well-constrained focal mechanisms using P-wave first motions. Of these, 60 also have mechanisms obtained by combining the P-wave first motions with the S-wave polarization directions. The observed seismicity is mainly located between 6 and 11 km depth. Most of the fault-plane solutions correspond to E-W-striking normal faulting, in agreement with the geological evidence. Most of the well-determined mechanisms indicate a nodal plane dipping 10–25° due north and a steep south-dipping plane. A similar asymmetry is also seen in the seismicity distribution and in the overall geological structure of the Corinth Rift. We discuss this evidence and the inference of a deep detachment zone, a structure where the major faults seen at the surface appear to root. A large part of the microseismic activity appears to cluster in regions near the junctions of the main faults with the proposed detachment zone. This feature of the microseismicity is interpreted in terms of stress transfer and stress concentration in regions of probable nucleation of future large earthquakes.}

During a 7-week microearthquake experiment conducted in Epirus, Akarnania, and the Ionian islands of western Greece, we located approximately 600 earthquakes with magnitudes between 2 and 4.2. No event was deeper than 40 km. The seismicity cannot be clearly associated with any single fault except the Lixourion right-lateral fault located west of the Ionian islands. Focal mechanisms of about 100 earthquakes show, for a narrow band of earthquakes located along the coast, ENE–WSW shortening consistent with the surface tectonics. Farther east, focal mechanisms show NNW–SSE extension beneath the foothills of the Pindus mountains, which is unrelated to surface faulting but is consistent with the presently subsiding basins. This strain pattern is seen far north and south of the Lixourion fault and is similar to the one observed in the Peloponnese. It suggests that a large-scale mechanism is responsible for the recent geodynamics of both the northwestern and southwestern Aegean