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To assess whether continental extension and seismic hazard are spatially-localized on single faults or spread over wide regions containing multiple active faults, we investigated temporal and spatial slip-rate variability over many millennia using in-situ 36 Cl cosmogenic exposure dating for active normal faults near Athens, Greece. We study a ~ NNE-SSW transect, sub-parallel to the extensional strain direction, constrained by two permanent GPS stations located at each end of the transect and arranged normal to the fault strikes. We sampled 3 of the 7 seven normal faults that exist between the GPS sites for 36 Cl analyses. Results from Bayesian inference of the measured 36 Cl data implies that some faults slip relatively-rapidly for a few millennia accompanied by relative quiescence on faults across strike, defining out-of-phase fault activity. Assuming that the decadal strain-rate derived from GPS applies over many millennia, slip on a single fault can accommodate ~ 30–75% of the regional strain-rate for a few millennia. Our results imply that only a fraction of the total number of Holocene active faults slip over timescales of a few millennia, so continental deformation and seismic hazard are localized on specific faults and over a length-scale shorter than the spacing of the present GPS network over this time-scale. Thus, (1) the identification of clustered fault activity is vital for probabilistic seismic hazard assessments, and (2) a combination of dense geodetic observations and palaeoseismology is needed to identify the precise location and width of actively deforming zones over specific time periods.

We studied the kinematic behaviour of active landslides at several localities in the area of Panachaikon Mountain, Achaia (Peloponnese, Greece) using Sentinel (C-band) InSAR time series analysis. We processed LiCSAR interferograms using the SBAS tool, and we obtained average displacement maps for the period 2016–2021. We found that the maximum displacement rate of each landslide is located at about the center of it. The average E-W velocity of the Krini landslide is ~3 cm/year (toward the east) and 0.6 cm/year downward. The line-of-sight (LOS) velocity of the landslide (descending orbit) compares well to a co-located GNSS station within (±) 3 mm/yr. Our results also suggest a correlation between rainfall and landslide motion. For the Krini landslide, a cross-correlation analysis of our data suggests that the mean time lag was 13.5 days between the maximum seasonal rainfall and the change in the LOS displacement rate. We also found that the amount of total seasonal rainfall controls the increase in the displacement rate, as 40–550% changes in the displacement rate of the Krini landslide were detected, following to a seasonal maximum of rainfall values at the nearby meteorological station of Kato Vlassia. According to our results, it seems that large part of this mountainous region of Achaia suffers from slope instability that is manifested in various degrees of ground displacement greatly affecting its morphological features and inhabited areas.

We investigated the post-seismic period of the March 2021 Damasi-Tyrnavos (Thessaly, Greece) normal fault earthquakes by applying the multi-temporal interferometric Small Baseline Subset method. We processed 68 ascending Sentinel-1 acquisitions between 2020/03/15 and 2022/09/12. Our results identified three areas on the hanging wall of the ruptured faults showing non-linear deformation trends (systematic motion away from the satellite), and another area, on the footwall (systematic motion towards the satellite), interpreted as due to a post-seismic effect. Inversion of the InSAR data indicated the occurrence of afterslip co-planar to the sequence’s two largest fault planes (M 6.3 and M 6.0, respectively). Most of the afterslip, with a peak of about 0.2 m, occurred on the fault corresponding to the 4 March 2021 event, at a depth of 7.5 km, while the fault corresponding to the M 6.3 event only showed very shallow adjustments and minor features at the border of the coseismic pattern. The transient uplift affected the footwall of the 3 March 2021 event and may indicate that the rupture nearly reached the surface towards the SW of the epicenter. The afterslip showed a fast phase lasting between March and August 2021 (5 months) and a second phase from March 2022 up to September 2022. A correlation between afterslip and relocated hypocenters indicates that most of the afterslip was aseismic. The moment release of the afterslip (fast phase) is about 7% that of the mainshocks.

The correlation of coseismic landslides with the seismic and morphological parameters has been investigated in detail by many researchers, mainly after the devastating 2008 M8.0 Wenchuan, China earthquake. One of the goals of such studies is to examine the spatial distribution of the earthquake-induced landslides in order to establish a pattern depending on the type of the seismic fault. This research focusses on the island of Lefkada, Ionian Sea, Greece, that is considered one of the most prone to earthquakes regions in Europe due to its proximity to the Cephalonia Transform fault. Landslide data from the two shallow strike-slip faulting earthquakes that occurred on 2003 and 2015 are statistically analyzed in order to evaluate the landslide magnitude and area of slope failures and their frequency-area size distributions. Furthermore, the spatial distribution of failures was investigated in detail regarding its correlation to topography (slope angle, aspect, local relief, elevation), geology, and the characteristics of fault rupture. We conclude that the landslide pattern is not controlled by a single parameter and that it results from a combination and interaction of seismic, morphological, and geological factors. In particular, the parameters of slope angle, geology, and fault rupture/asperities are the ones that are clearly related to the highest landslide densities.

The South East Aegean Sea is seismically active with crustal and intermediate-depth earthquakes of magnitude that can exceed the magnitude Mw = 7. On July 20, 2017, a shallow normal faulting Mw = 6.6 earthquake occurred in the Gulf of Gökova, 10 km away from the cities of Kos and Bodrum. A tsunami hit the coasts of Turkey and Kos Island with waves of up to 2 m that damaged several harbors. Based on the field surveys and the tide-gauge records of Bodrum, Syros and Kos harbors, we performed tsunami simulations to constrain the source and analyze the North v/s South-dipping solutions for the fault plane. Depending on the source model, the simulations show different height distributions which provide complementary constrains on the source parameters, helping the characterization of the fault plane. The comparison between our maximum wave heights models and the field data favor the North-dipping fault scenario. When using only the constraint of the Bodrum tide-gauge, our models lead to a source with a 0.7 m fault slip, incompatible with the slip inferred from geodesy. When using the constrain from neighboring coastal wave heights and run-up recovered during field surveys, the best fit is obtained with a 2 m fault slip scenario consistent with the geodetic models. There is a 0.25 m mean difference between observed and synthetic water heights that could be due to the unaccuracy of the bathymetry data.

Knowledge and visualization of the present-day relationship between earthquakes, active tectonics and crustal deformation is a key to understanding geodynamic processes, and is also essential for risk mitigation and the management of geo-reservoirs for energy and waste. The study of the complexity of the Greek tectonics has been the subject of intense efforts of our working group, employing multidisciplinary methodologies that include detailed geological mapping, geophysical and seismological data processing using innovative methods and geodetic data processing, involved in surveying at various scales. The data and results from these studies are merged with existing or updated datasets to compose the new Seismotectonic Atlas of Greece. The main objective of the Atlas is to harmonize and integrate the most recent seismological, geological, tectonic, geophysical and geodetic data in an interactive, online GIS environment. To demonstrate the wealth of information available in the end product, herein, we present thematic layers of important seismotectonic and geophysical content, which facilitates the comprehensive visualization and first order insight into seismic and other risks of the Greek territories. The future prospect of the Atlas is the incorporation of tools and algorithms for joint analysis and appraisal of these datasets, so as to enable rapid seismotectonic analysis and scenario-based seismic risk assessment.

Remains of past sea levels such as tidal notches may provide valuable information for the investigation of relative sea-level changes (RSL) of eustatic/tectonic origin. In this review, we focus on case studies of coastal changes from the Corinth Gulf, where impacts of past earthquakes can be traced through various indicators. The southern coast has undergone a tectonic uplift during the Holocene, whereas the northern coast has undergone subsidence. The magnitude of RSL fall in the south Corinth Gulf is larger than RSL rise in the north. Exploiting previous measurements and datings, we created a geodatabase regarding the relative sea-level changes of the whole gulf, including geodetic data based on permanent GNSS observations. The combination of geomorphological (long-term) and geodetic (short-term) data is a key advance for this area, which is characterized by fast rates of N-S crustal extension and strong earthquakes. The joint dataset fits the tectonic model of an active half-graben where the hanging wall (northern coast) subsides and the footwall (southern coast) is uplifted. The highest uplift rates (3.5 mm/year) are near Aigion, which indicates an asymmetric localization of deformation inside this active rift.

We combine almost 10 years of continuous GNSS observations at four permanent stations with groundwater and rainfall data to investigate subsidence patterns in the region of Thessaly, central Greece. Thessaly is a key area for studying anthropogenic versus tectonic subsidence in Greece because it is (a) characterized by overexploitation of groundwater reservoirs since the 1980s and (b) has a Twentieth-century history of shallow, normal-slip earthquakes with M > 6. We infer that anthropogenic subsidence continues at southeast Thessaly (Karla reservoir region) up to autumn of 2017 because the vertical time-series data of station STEF (Stefanovikio) reach a cumulative value of 55 cm and show a “ramp-flat” pattern that correlates with neighboring borehole data. The geodetic data from other three examined regions (city of Larissa, city of Karditsa and Klokotos) indicate ground stability. The GNSS stations in Karditsa (KRDI) and Larissa (LARM) show correlation with groundwater-level fluctuations but no subsidence. Station KLOK (Klokotos) shows a small subsiding trend (− 0.38 mm/yr) with no correlation to either groundwater levels or to rainfall patterns; therefore, its seasonal periodicity may reflect geodynamic (plate) motions.

The triggering of slope failures can cause a significant impact on human settlements and infrastructure in cities, coasts, islands and mountains. Therefore, a reliable evaluation of the landslide hazard would help mitigate the effects of such landslides and decrease the relevant risk. The goal of this paper is to develop, for the first time on a regional scale (1:100,000), a landslide susceptibility map for the entire area of the Attica region in Greece. In order to achieve this, a database of slope failures triggered in the Attica Region from 1961 to 2020 was developed and a semi-quantitative heuristic methodology called Rock Engineering System (RES) was applied through an interaction matrix, where ten parameters, selected as controlling factors for the landslide occurrence, were statistically correlated with the spatial distribution of slope failures. The generated model was validated by using historical landslide data, field-verified slope failures and a methodology developed by the Oregon Department of Geology and Mineral Industries, showing a satisfactory correlation between the expected and existing landslide susceptibility level. Having compiled the landslide susceptibility map, studies focusing on landslide risk assessment can be realized in the Attica Region.

This is the first landslide inventory map in the island of Lefkada integrating satellite imagery and reports from field surveys. In particular, satellite imagery acquired before and after the 2003 earthquake were collected and interpreted with the results of the field survey that took place 1 week after this strong (Mw = 6.3) event. The developed inventory map indicates that the density of landslides decreases from west to east. Furthermore, the spatial distribution of landslides was statistically analyzed in relation to the geology and topography for investigating their influence to landsliding. This was accomplished by overlaying these causal factors as thematic layers with landslide distribution data. Afterwards, weight values of each factor were calculated using the landslide index method and a landslide susceptibility map was developed. The susceptibility map indicates that the highest susceptibility class accounts for 38 % of the total landslide activity, while the three highest classes that cover the 10 % of the surface area, accounting for almost the 85 % of the active landslides. Our model was validated by applying the approaches of success and prediction rate to the dataset of landslides that was previously divided into two groups based on temporal criteria, estimation and validation group. The outcome of the validation dataset was that the highest susceptibility class concentrates 18 % of the total landslide activity. However, taking into account the frequency of landslides within the three highest susceptibility classes, more than 85 %, the model is characterized as reliable for a regional assessment of earthquake-induced landslides hazard.