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.

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.

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.

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 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.

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.

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.

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.