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.

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.

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

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.

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.

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.