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The Church of Panaghia Krena is a very important Byzantine monument situated in the island of Chios, well-known due to the high aesthetic value of the ceramic tile decoration on its facades and of its frescoes. The church suffered severe damage especially due to the 1881 devastating Chios earthquake and different interventions were implemented soon after (1884), consisting mainly of the reconstruction of collapsed areas and the addition of ties. Nevertheless, deterioration of old damages and appearance of new ones was observed. Thus, a restoration program was carried out between 2000 and 2007. This paper presents the basic characteristics of all types of historic materials examined, the main results of the in situ and laboratory experimental program carried out for the selection of the raw materials, and the design of optimum compositions of mortars and grouts to be used for the restoration works. The importance of in situ pilot applications is underlined, as well as of the production of site-specific aggregates for the repointing mortars by crushing a local rock, in order to succeed the adequate reddish color to match with the original mortars and bricks still preserved and achieve an aesthetic harmony with the color hue and texture of the original materials. [ABSTRACT FROM AUTHOR]

This study employs advanced synthetic aperture radar (SAR) techniques, specifically the small baseline subset (SBAS) method, to analyze ground deformation dynamics on Aegina, a volcanic island within the Hellenic Volcanic Arc. Using Sentinel-1 satellite data spanning January 2016 to May 2023, this research reveals different deformation behaviors. The towns of Aegina and Saint Marina portray regions of stability, contrasting with central areas exhibiting subsidence rates of up to 1 cm/year. The absence of deformation consistent with volcanic activity on Aegina Island aligns with geological records and limited seismic activity, attributing the observed subsidence processes to settlement phenomena from past volcanic events and regional geothermal activity. These findings reinforce the need for continuous monitoring of the volcanic islands located in the Hellenic Volcanic Arc, providing important insights for local risk management, and contributing to our broader understanding of geodynamic and volcanic processes. [ABSTRACT FROM AUTHOR]

Until the Mw 6.6 Luding earthquake ruptured the Moxi section of the Xianshuihe fault (XSHF) on 5 September 2022, the region had not experienced an Mw >6 earthquake since instrumental records began. We used Global Positioning System (GPS) and Sentinel-1 interferometric synthetic aperture radar (InSAR) observations to image the coseismic deformation and constrain the location and geometry of the seismogenic fault using a Bayesian method We then present a distributed slip model of the 2022 Mw6.6 Luding earthquake, a left-lateral strike-slip earthquake that occurred on the Moxi section of the Xianshuihe fault in the southwest Sichuan basin, China. Two tracks (T26 and T135) of the InSAR data captured a part of the coseismic surface deformation with the line-of-sight displacements range from ∼−0.16 m to ~0.14 m in the ascending track and from ~−0.12 m to ~0.10 m in the descending track. The inverted best-fitting fault model shows a pure sinistral strike-slip motion on a west-dipping fault plane with a strike of 164.3°. We adopt a variational Bayesian approach and account for the uncertainties in the fault geometry to retrieve the distributed slip model. The inverted result shows that the maximum slip of ~1.82 m occurred at a depth of 5.3 km, with the major slip concentrated within depths ranging from 0.9–11 km. The InSAR-determined moment is 1.3 × 1019 Nm, with a shear modulus of 30 GPa, equivalent to Mw 6.7. The published coseismic slip models of the 2022 Luding earthquake show apparent differences despite the use of similar geodetic or seismic observations. These variations underscore the uncertainty associated with routinely performed source inversions and their interpretations for the underlying fault model. [ABSTRACT FROM AUTHOR]

Instrumental earthquake monitoring in Greece started in 1899–1906 with the first five seismic stations of the National Observatory of Athens, Institute of Geodynamics (NOA). Subsequent upgrades and expansions led to today's Unified National Seismic Network, which includes almost all permanent seismic stations in Greece and provides waveform and parametric data. We examine the detection capabilities of the Greek seismic networks using phase, location and magnitude data from the International Seismological Centre (ISC) and the various National Institutes. We apply two methods to measure the network performance. In one, we form a grid, and find the 50 per cent probability detection threshold for each station-grid cell pair for different times. In the other, we find the probability-based magnitude of completeness grid for every three months from 1970 to 2014. Both methods show that in 1990 the detection threshold improved significantly in the north part of Greece. A much greater improvement took place in 2010 throughout Greece, yielding a completeness magnitude of |$M_p\, \sim$| 1. [ABSTRACT FROM AUTHOR]

The mining area in western China is ecologically sensitive. Coal mining can cause the formation of ground fissures, leading to geological disasters and further accelerating the process of land desertification. In this study, the working face of non-coal-pillar mining in the aeolian sand area was considered as the research object. The movement and deformation law of overlying strata were investigated through field measurements, theoretical analysis, and numerical simulation, and the mechanism governing the self-healing characteristics of ground fissures was revealed. The results demonstrated that the surface angular parameters were lower. This implies that the surface movement and the degree of deformation in non-coal-pillar mining in the aeolian sand area are significant, with a large mining influence range and rapid surface subsidence speed. After the mining of the working face, the resulting failure form of the overlying rock was asymmetric. Boundary ground fissures are typically located within the boundary of the working face, and no outward expansion is primarily observed. Dynamic ground fissures have "waviness" morphological characteristics and asymmetric "M" type development characteristics. A location model as well as a development cycle model of dynamic ground fissures were established for the first time, which can be used to predict the location and period of ground fissures. Based on the motion characteristics of hinged rock block structures, the mechanical mechanism of the self-healing phenomenon of dynamic ground fissures was revealed. A partition monitoring mode of working faces without coal pillar mining was proposed for the first time, which can reduce a lot of manpower and material resources. The coal mining subsidence basin is divided into a natural restoration area and an artificial restoration area. The combination of natural restoration and artificial guidance was used to control the ground fissures and reduce the associated costs. The research conclusions can provide a basis for mining damage evaluation and ecological environment protection in the aeolian sand area. [ABSTRACT FROM AUTHOR]

An effort is exerted to investigate the recurrence pattern of large earthquakes (Mw ≥ 6.0) in the Kefalonia Transform Fault Zone (KTFZ), Greece, by considering the incorporation of the 74-year (1948–2022) evolving stress field. Four earthquake occurrence models—the Poisson, Poisson with the incorporation of the static stress changes (Poisson + ΔCFF), Brownian passage time (BPT) and Brownian passage time with the incorporation of the static stress changes (BPT + ΔCFF)—have been applied to estimate the occurrence probabilities of nearly characteristic earthquakes for the seven fault segments of the study area. The mean recurrence time, Tr, is estimated using the physics-based seismic moment rate conservation method. The results show large variability depending upon fault parameters. Incorporating the state of stress into Tr results in both advanced and delayed recurrence patterns. The occurrence probability estimates for the next 10, 20 and 30 years indicate that the fault segment most likely to be ruptured is the Paliki North fault segment in all models. Overall, the occurrence probabilities, combined with the state of stress along the fault segments, emphasize the high seismic moment rate of the study area. The application of time-dependent models (BPT, BPT + ΔCFF) resulted in significant increases or decreases in the associated seismic hazard. [ABSTRACT FROM AUTHOR]

Satellite geodesy, an indispensable modern tool for determining upper-crust deformation, can be used to assess tectonically active structures and improve our understanding of the geotectonic evolution in tectonically active regions. A region fulfilling these criteria is the North Aegean, part of the Eastern Mediterranean. It is one of the most tectonically, and hence, seismically, active regions worldwide, which makes it ideal for applying a satellite geodesy investigation. Although many regional studies have been carried out across the entire Aegean region, there are three more focused case studies that provide better resolution for different parts of the North Aegean. The synthesis of these case studies can lead to an overall geodynamic assessment of the North Aegean. The North Aegean Sea case study is characterized by the North Aegean Trough (NAT), which is directly associated with the westward prolongation of the North Anatolian Fault (NAF). Both NE–SW normal and strike-slip faulting have been documented in this offshore region. Geodetic analysis considers geodetic data, derived from 32 permanent GPS/GNSS stations (recorded for the 2008–2014 time period). This results in the estimation of the Maximum (MaHE) and Minimum (MiHE) Horizontal Extension, Maximum Shear Strain (MSS) and Area Strain (AS) parameters, based on triangular methodology implementation; the same strain parameters have similarly been estimated for the Strymon and Thessalian basins, respectively. The Strymon basin (first case study) is located in the central part of the northern Greek mainland, and it is dominated by NW–SE (up to E–W) dip-slip normal faults; this area has been monitored by 16 permanent GPS/GNSS stations for seven consecutive years. Regarding the Thessalian basin case study, E–W, dip-slip and normal faults are noted at the basin boundaries and within the Thessalian plain. This region has also been monitored for seven consecutive years by 27 permanent GPS/GNSS stations. However, this case study is characterized by a strong seismic event (Mw6.3; 3 March 2021), and thus all strain parameters depicted the pre-seismic deformation. Analysis of these three different case studies confirmed the current tectonic setting of the North Aegean region, while revealing new aspects about the geodynamic evolution of the wider region, such as highlighting areas with significant tectonic activity and the crucial role of strike-slip faulting in the broader Aegean region. [ABSTRACT FROM AUTHOR]

The current research aims to examine the long-term evolution of the western cliffs of Lefkada Island following the occurrence of the last two strong earthquakes, on 14 August 2003 and 17 November 2015, respectively. Medium resolution satellite data (Landsat) and very high-resolution data (Ikonos, Pleiades, and airphotos) were processed in Google Earth Engine and Erdas imagine software, respectively. The study area covers a 20 km-long region of the western cliffs of Lefkada Island, extending from Egremni beach to the South to Komilio beach to the North. Relief, vegetation, and inclination changes were detected in the ArcGis environment. The results were associated with in situ data provided through the installation of a sediment trap. The analysis of the results proved that seismicity is the main factor that formed the western coastline of Lefkada Island, affecting the integrity of the cliffs. Specifically, large earthquakes cause immediate vegetation and topographic (inclination changes, mass movements) modifications in the western cliffs of the island. Meanwhile, small earthquakes (magnitudes < 4.1) contribute to the cliff's evolution during the inter-seismic era. The intensity of these aforementioned changes was closely related to the seismic activity that occurred in the vicinity of the study area. In addition, it was found that precipitation and wind do not exert a similar influence on the cliff's evolution. [ABSTRACT FROM AUTHOR]

Probabilistic Seismic Hazard Assessment (PSHA) was carried out for the administrative region of Attica (Greece). Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) values were calculated for return periods of 475 and 950 years for five sub-areas covering the entire region. PGA hazard curves and Uniform Hazard Spectra (UHS) in terms of spectral acceleration (Sa) values were generated for Athens, Methana, and the capitals of each island of Attica (Salamina, Aegina, Poros, Hydra, Spetses, Kythira, and Antikythira). Area sources were adopted from the Euro-Mediterranean Seismic Hazard Model 2013 (ESHM13) and its update, ESHM20, taking into account both crustal and slab tectonic environments. Ground Motion Prediction Equations (GMPEs) proposed for the Greek territory were ranked for PGA and PGV. Each GMPE was reconstructed as a weighted model, accounting for normal and non-normal focal mechanisms for each area source. PGA, PGV, and Sa values were computed using a logic tree, integrating the seismotectonic models as major branches and sub-logic trees, comprised of multiple ranked GMPEs for each area source, as minor branches. The results showed higher seismic hazard values in sub-areas near the Gulf of Corinth and the slab interface, which could indicate a need to revise the active building code in Attica. [ABSTRACT FROM AUTHOR]

The Weihe Basin is a crucial part of the Fenwei Graben System and is a typical example of an extensional fault basin. Over time, the region has been developed around 212 ground fissures, with the majority of them being associated with heavy rainfall. These water-eroded ground fissures have caused serious damage to farmland, houses, and roads, with the Liangjiacun ground fissures, Meiyuancun ground fissures, and Dizhentai ground fissures being the most known. To understand the developmental characteristics and formation mechanisms of water-eroded ground fissures in the Weihe Basin, we utilized a variety of methods, including ground surveys, mapping, trenching, drilling, and geophysical exploration. These three ground fissures are distributed along corresponding fault zones, with their orientations being closely linked to local topographic changes. Additionally, the trenching profiles showed that all three typical ground fissure zones have distinct hidden holes above the paleosol. The formation of these ground fissures is closely associated with tectonic activity and heavy rainfall, with soil ruptures resulting from tectonic activity becoming the dominant channels for surface water infiltration. Furthermore, the erosion caused by heavy rainfall accelerates the rupture and expansion of ground fissures in the shallow subsurface. This paper is a valuable resource for disaster prevention and mitigation strategies aimed at mitigating the damage caused by ground fissures in the Weihe Basin. [ABSTRACT FROM AUTHOR]

Rockfall analysis is a multiparametric procedure with many uncertainties and the outputs are largely dependent on some critical engineering geological parameters involved in the used simulation model. In this paper, three completely different limestone rock sequences, named Pantokratoras, Vigla, and Paxos limestones along the western coastal slopes of Lefkada island, in Greece, are examined regarding their rockfall susceptibility as expressed by produced kinetic energy, under aseismic and seismic conditions. A rockfall inventory was prepared through detailed field measurements after the extensive rockfalls which were caused by the strong earthquake of November 2015, while engineering geological surveys were systematically conducted on the limestone rock masses. Two case scenarios were adopted for the rockfall simulations: one without the horizontal initial velocity of the detached rock boulder and the other with an estimated value obtained from the peak ground velocity (PGV) of the main seismic shock. Two-dimensional rockfall simulations were performed in selected cross-sections for each rock mass, and spatial distribution maps of the intensity (kinetic energy) were generated. A comparison of the maps has shown a strong maximum variation in the intensity levels among the three rock masses mainly due to the differential size of the detached boulders because of the inherent engineering geological characteristics of the rock masses. The results show that the earthquake ground velocity generally leads to a fluctuating change in the intensity values due to the trajectory shape and increases the rockfall magnitude as the main triggering factor. [ABSTRACT FROM AUTHOR]

Lefkada and Corfu old towns are located in the western part of Greece, in the Ionian Sea. Their proximity to the Hellenic subduction zone (HSZ) is the reason for their intense seismicity. The main goal of this study was the estimation of the geotechnical characteristics of the subsurface, with the contribution of applied geophysical techniques. Therefore, seismic refraction tomography (SRT) and multichannel analysis of surface waves (MASW) were applied. A total of thirty-three (33) seismic and geoelectrical profiles were performed in both towns in order to evaluate the geotechnical characteristics of the subsurface formations. Additionally, subsurface resistivity distributions were investigated with the application of electrical resistivity tomography (ERT). Some important elastic moduli were calculated through the combination of estimated seismic wave velocities and laboratory density measurements. The horizontal distribution of seismic velocities and mechanical properties (σ, E, K, G) of Corfu town was illustrated in maps, for the depth of 5 m. The geophysical interpretation also revealed that Lefkada's subsurface consists of only one compact geological formation, with little or no variation of its geophysical-geotechnical characteristics. Beyond that, the ground type classifications for the two towns were determined according to the European Committee for Standardization Eurocode 8, based on VS30 values. [ABSTRACT FROM AUTHOR]

Underground mining activity in the karst mountain in southwestern China has induced several large-scale rocky landslides and has caused serious casualties. At present, there is a lack of systematic research on the formation mechanism of landslides in this area using multi-method fusion technology. First, the orthophoto images of the landslide area obtained by UAV photography were used to analyze the deformation characteristics of the landslide. Second, the failure characteristics of the strata overlying the goaf were analyzed by geophysical detection. Finally, the deformation response characteristics of the mountain under underground mining were analyzed by UDEC numerical simulation. The results revealed that during the underground mining, the failure process of the mountain occurred in four stages: fracture expansion, subsidence and collapse, shear sliding, and multi-level sliding. Gently dipping soft–hard alternant strata and a blocky rock mass structure formed the geological foundation of the landslides. Underground mining accelerated the fracturing of the overlying strata and the formation of a stepped penetrating sliding surface. Tensile movement of the structural planes of hard sandstone in the free face, and shear sliding of the weak mudstone layer, were the main causes of the landslides. The slope instability mode was tension-shear fracturing, shear sliding, back toppling, and compressive shear failure. In addition, the fracture propagation in the overlying strata and damaged geological structure revealed by the geophysical detection were consistent with the simulation results. This study provides ideas for the precise countermeasures of disaster prevention and mitigation for similar landslides in this area. [ABSTRACT FROM AUTHOR]

We propose a spatiotemporal point process model that enhances the classical Epidemic‐Type Aftershock Sequence (ETAS) model. This is achieved with the introduction of a renewal main‐shock arrival process and we call this extension the renewal ETAS (RETAS) model. This modification is similar in spirit to the renewal Hawkes (RHawkes) process but the conditional intensity process supports a spatial component. It empowers the main‐shock intensity to reset upon the arrival of main‐shocks. This allows for heavier clustering of main‐shocks than the classical spatiotemporal ETAS model. We introduce a likelihood evaluation algorithm for parameter estimation and provide a novel procedure to evaluate the fitted model's goodness‐of‐fit (GOF) based on a sequential application of the Rosenblatt transformation. A simulation algorithm for the RETAS model is outlined and used to validate the numerical performance of the likelihood evaluation algorithm and GOF test procedure. We illustrate the proposed model and methods on various earthquake catalogues around the world each with distinctly different seismic activity. These catalogues demonstrate the RETAS model's additional flexibility in comparison to the classical spatiotemporal ETAS model and emphasizes the potential for superior modelling and forecasting of seismicity. [ABSTRACT FROM AUTHOR]

The Gulf of Corinth (Central Greece) is one of the most rapidly extending rifts worldwide, with its western part being the most seismically active, hosting numerous strong (M ≥ 6.0) earthquakes that have caused significant damage. The main objective of this study was the evaluation of seismic hazard through a probabilistic and stochastic methodology. The implementation of three seismotectonic models in the form of area source zones via a logic tree framework revealed the expected level of peak ground acceleration and velocity for return periods of 475 and 950 years. Moreover, PGA values were obtained through the stochastic simulation of strong ground motion by adopting worst-case seismic scenarios of potential earthquake occurrences for known active faults in the area. Site-specific analysis of the most populated urban areas (Patras, Aigion, Nafpaktos) was performed by constructing uniform hazard spectra in terms of spectral acceleration. The relative contribution of each selected fault segment to the seismic hazard characterizing each site was evaluated through response spectra obtained for the adopted scenarios. Almost all parts of the study area were found to exceed the reference value proposed by the current Greek National Building Code; however, the three urban areas are covered by the Eurocode 8 regulations. [ABSTRACT FROM AUTHOR]

Forecasting the spatio-temporal occurrence of events is at the core of Operational Earthquake Forecasting, which is of great interest for risk management, particularly during ongoing seismic sequences. Epidemic type aftershock sequence (ETAS) models are powerful tools to estimate the occurrence of events during earthquake sequences. In this context, a robust seismicity forecasting framework based on Bayesian-inference has been adapted to the Patras and Aegio region in western Greece (one of the most seismically active parts of Mediterranean), and an incremental adaptive algorithm is introduced to train the priors for ETAS model parameters. The seismicity forecasting is capable of accounting for uncertainty in the model parameters as well as variations in the sequence of events that may happen during the forecasting interval. Six seismic sequences between 1995 and 2018 were selected with main shock moment magnitudes M w ≥ 6.0. The ETAS model was adapted for each seismic sequence. The number of forecasted events with M w ≥ 4.5 and their spatial distribution was retrospectively compared with the as-recorded earthquake catalogue, confirming a good agreement between the forecasts and observations. The results show that the adapted model can be used immediately after a severe main shock to statistically predict potentially damaging earthquakes during the ongoing seismic sequence. The seismicity forecasts were translated to short-term daily exceedance rates for different thresholds of peak ground acceleration. The results reveal that the seismic hazard increased by up to 33 times in the case of the damaging 1995 M w 6.5 earthquake in the city of Aegio. However, the results confirmed that in all six studied sequences, the increased seismic hazard decayed rapidly during the 2 d after the main shock, and remained relatively high in the following days (roughly ten times the long-term time-independent hazard). [ABSTRACT FROM AUTHOR]

One of the most critical stages in fault-slip data stress analysis is separating the fault data into homogeneous subsets and selecting a suitable analysis method for each subset. A basic assumption in stress tensor computations is that fault activations occur simultaneously under a homogeneous stress regime. With that rationale, this work aims to attain improvements in the paleostress reconstruction from the polyphase deformed region of Voltri Massif in the Ligurian Alps by using already published heterogeneous fault-slip data inverted using best-fit stress inversion methods and in the absence of any tectonostratigraphic and overprinting criteria. The fault-slip data are re-examined and analyzed with a best-fit stress inversion method and the Tensor Ratio Method (TRM) in the absence of any tectonostratigraphic and overprinting criteria. This analysis defines crucial differences in the paleostress history of the Voltri Massif in the Ligurian Alps, and gives insight into the analysis and results of different stress inversion methodologies. Best-fit site stress tensors have substantial diversity in stress orientations and ratios, implying possible stress perturbations in the region. The reason for these diversities is that the Misfit Angle (MA) minimization criterion taken into account in the best-fit stress inversion methods allows for acceptable fault-slip data combinations, which under the additional geological compatibility criteria used by the TRM, are found to be incompatible. The TRM application on this already published and analyzed data defines similar site and bulk stress tensors with fewer diversities in stress orientations and ratios defined from fault-slip data whose orientations always satisfy the same additional geological compatibility criteria induced by the TRM, and not only from the MA minimization criterion. Thus, TRM seems to define stress tensors that are not as sensitive to the input of fault-slip data, compared to the best-fit stress tensors that appear to suffer from the 'overfitting' modeling error. Five distinct TRM bulk paleostress tensors provide a more constrained paleostress history for the Voltri Massif and the Ligurian Alps, which after the restoration of the ~50° CCW rotation, comprise: (a) a transpression–strike-slip stress regime (T1) with NNE-SSW contraction in Late Eocene, (b) an Oligocene NW-SE extensional regime (T2), which fits with the NW-SE extension documented for the broader area north of Corsica due to a significant change in subduction dynamics, (c) a transient, local, or ephemeral NE-SW transtension (T3) which might be considered a local mutual permutation of the T2 stresses, and (d) a Miocene transpression with a contraction that progressively shifted from ENE-WSW (T4) to NNE-SSW (T5), reflecting the stress reorganization in the Ligurian Alps due to a decrease in the retreating rate of the northern Apennines slab. Therefore, paleostress reconstruction can be fairly described by enhanced Andersonian bulk stress tensors, and requires additional geological compatibility criteria than the criteria and sophisticated tools used by the best-fit stress inversion methods for separating the fault-slip data to different faulting events. [ABSTRACT FROM AUTHOR]

Nearly 20 years ago, the observation that major earthquakes are generally preceded by an increase in the seismicity rate on a timescale from months to decades was embedded in the "Every Earthquake a Precursor According to Scale" (EEPAS) model. EEPAS has since been successfully applied to regional real-world and synthetic earthquake catalogues to forecast future earthquake occurrence rates with time horizons up to a few decades. When combined with aftershock models, its forecasting performance is improved for short time horizons. As a result, EEPAS has been included as the medium-term component in public earthquake forecasts in New Zealand. EEPAS has been modified to advance its forecasting performance despite data limitations. One modification is to compensate for missing precursory earthquakes. Precursory earthquakes can be missing because of the time-lag between the end of a catalogue and the time at which a forecast applies or the limited lead time from the start of the catalogue to a target earthquake. An observed space-time trade-off in precursory seismicity, which affects the EEPAS scaling parameters for area and time, also can be used to improve forecasting performance. Systematic analysis of EEPAS performance on synthetic catalogues suggests that regional variations in EEPAS parameters can be explained by regional variations in the long-term earthquake rate. Integration of all these developments is needed to meet the challenge of producing a global EEPAS model. [ABSTRACT FROM AUTHOR]

Strong crustal earthquakes in Greece are typically followed by aftershocks, the properties of which are important factors in seismic hazard assessment. In order to examine the properties of earthquake sequences, we prepared an earthquake catalog comprising aftershock sequences with mainshocks of Mw ≥ 5.5 from 1995 to 2021. Regional aftershock parameters were estimated to highlight variations in aftershock decay and productivity among regions with similar seismotectonic characteristics. A statistically based method of estimating aftershock duration and a metric of relative aftershock productivity to examine the variations among the different cases were employed. From the detailed analysis of the selected seismic sequences, we attempt to unravel the physical mechanisms behind deviations in aftershock duration and productivity and resolve the relative contribution of background seismicity, the Omori–Utsu law parameters and the mainshock faulting properties. From our analysis, the duration of aftershock sequences depends upon the rupture process of the mainshock, independently of its magnitude. The same applies to aftershock productivity, however, other tectonic setting (e.g., seismic coupling) or source-related (e.g., focal depth, stress drop) parameters also contribute. The estimated regional parameters of the aftershock rate models could be utilized as initial ones to forecast the aftershock occurrence rates at the early stage following a mainshock. [ABSTRACT FROM AUTHOR]

The three aftershock sequences that occurred in Al Hoceima, Morocco, in May 1994 (Mw 6.0), February 2004 (Mw 6.4) and January 2016 (Mw 6.3) were stochastically modeled to investigate their temporal and energetic behavior. A form of the restricted trigger model known as the restricted epidemic type aftershock sequence (RETAS) was used for the temporal analysis of the selected series. The best-determined fit models for each sequence differ based on the Akaike information criteria. The revealed discrepancies suggest that, although the activated fault systems are close (within 10 to 20 km), their stress regimes change and shift across each series. In addition, a stochastic model was presented to study the strain release following a specific strong earthquake. This model was constructed using a compound Poisson process and depicted the progression of the strain release during the aftershock sequence. The proposed model was then applied to the data. After the RETAS model was used to evaluate the behavior of the aftershock decay rate, the best-fit model was obtained and integrated into the strain-release stochastic analysis. By detecting the potential disparities between the observed data and model, the applied stochastic model of strain release allows for a more comprehensive examination. Furthermore, comparing the observed and expected cumulative energy release numbers revealed some variations at the start of all three sequences. This demonstrates that significant aftershock clusters occur more frequently shortly after the mainshock at the start of the sequence rather than if they are assumed to occur randomly. [ABSTRACT FROM AUTHOR]

Abstract—A detailed study has been carried out regarding temporal variations of seismicity in the region of Greece's eastern coast of the Aegean Sea, where, in the vicinity of Samos Island, a catastrophic earthquake with M = 6.7 occurred on October 30, 2020. Seismicity has been analyzed by use of the the parameter b of the Gutenberg-Richter law, the value of released seismic energy in the form logE2/3, and the indicator of seismic activity logN. The analysis results have shown that the studied earthquake was preceded by confidently distinguished anomalies of the seismic parameters, which lasted for about 15 years. Similar anomalies lasting about 4–6 years were observed before 5 strong earthquakes with magnitudes M ≥ 5.5 that have occurred in the same region over the past 50 years. It is shown that the amplitudes of temporal anomalies increase as the earthquake sampling approaches the depths of the strong event preparation sources. It is concluded that the dependence of the amplitude of temporal variations of the seismic parameters on depth can be used to estimate the depth of future strong event sources. Studies of temporal variations of seismicity in three independent seismically active regions, in the vicinity of Lesbos Island, Samos Island, and Kos Island, show that, in the period from 2010 to 2020, before the three strong earthquakes with magnitudes M ≥ 6.1 that occurred in these regions, there are observed precursors of the studied parameters. The spatio-temporal sequence of the occurrence of these events is explained in terms of the seismic gap formation concept in the vicinity of Samos Island. An assumption is made about detection of a deformation wave with the front propagating in the direction from NNW to SSE at a velocity of 40–50 km/year in the region of the eastern coast of the Aegean Sea during the period from 2005 to 2020. Considerations are put forward that in the next years (10–15), in this region in the area between Lesbos Island and Kos Island, the occurrence of strong earthquakes with М ≥ 6.1 is unlikely. At the same time, it is not excluded that in the next 2–3 years to the south of Kos Island, in the region of Rhodos Island, there might be a strong earthquake with M ≈ 6.0–6.5. [ABSTRACT FROM AUTHOR]

The Aegean–Hellenic arc is a deformed sector of a long heterogeneous orogenic system (Tethyan belt), constituted by an inner old metamorphic crystalline core flanked by younger chains of European and African affinity, running from the Anatolian to the Pelagonian zones. Due to the convergence between the Arabian promontory and the Eurasian continental domain, the Anatolian sector of that belt has undergone a westward extrusion, accommodated by oroclinal bending, at the expense of the surrounding low buoyancy domains. Since the late Miocene, when the Aegean Tethyan belt collided with the Adriatic continental promontory, the southward bowing of the Aegean–Hellenic sector accelerated, leading to the consumption of the Levantine and Ionian oceanic domains and to the formation of the Mediterranean Ridge accretionary complex. The peculiar distribution of extensional and compressional deformation in the Aegean zone has mainly been influenced by the different rheological behaviours of the mainly ductile inner core (Cyclades arc) and of the mainly brittle outer belt (Hellenic arc). The bowing of the inner belt developed without involving any major fragmentation, whereas the outer brittle belt underwent a major break in its most curved sector, which led to the separation of the eastern (Crete–Rhodes) and western (Peloponnesus) Hellenic sectors. After separation, these structures underwent different shortening patterns, respectively driven by the convergence between southwestern Anatolia and the Libyan continental promontory (Crete–Rhodes) and by the convergence between the Cycladic Arc and the Adriatic continental domain (Peloponnesus). A discussion is given about the compatibility of the observed deformation pattern with the main alternative geodynamic interpretations and with the Nubia–Eurasia relative motions so far proposed. [ABSTRACT FROM AUTHOR]

Coastal areas constitute a very dynamic environment, balancing between numerous natural and anthropogenic processes liable to sometimes hazardous geomorphic phenomena. Especially in tectonically active coastal regions and areas of high economic value, slope failures can have significant impacts and therefore need careful and detailed examination. This work uses Unmanned Aerial System (UAS)-aided photogrammetry and Terrestrial Laser Scanning (TLS) in tectonically active segments of the coastal zone of the Ionian Islands in Greece, to explore how their capabilities can help to improve our understanding of the structural integrity of the slopes. Results show that the two approaches are able to extract large numbers of discontinuity facets, in a more practical, rapid and safe way than conventional methods of rock slope stability analysis extending to unreachable yet important parts of the slope. Through this holistic record of the structural condition of the slope the two applications allow the identification of segments that are more prone to instability and failure. In this way, they improve our understanding of the prioritization of interventions aiming to enhance the prevention of slope failures, mitigating the associated risk and improving local development in these high-value locations. [ABSTRACT FROM AUTHOR]

Underground coal mining inevitably causes ground fissures, especially permanent cracks that cannot be closed at the boundary of the working face. Studying the underground three-dimensional morphology of the permanent cracks allows one to accurately constrain the formation and development of the ground fissures. This information will contribute to reducing mine disasters and is also a prerequisites to avoid environmental pollution. We selected the Zhangjiamao coal mine (China), which is situated in a collapsible loess area, as a case study for deciphering the formation of permanent cracks. After injecting gypsum slurry into the mine, a three-dimensional model of the ground fissures is obtained by three-dimensional (3D) laser scanner technology that records the 3D underground morphology. Integrating the geological context of a collapsible loess area, the characteristics and main processes of the ground fissure development are constrained: (1) The width of the ground fissure decreases to 0 with increasing depth and is strongly affected by the soil composition. (2) Along the vertical extension direction, the ground fissures are generally inclined to the inner-side of the working face, but the direction remains uncertain at different depths. (3) The transverse propagation direction of the ground fissure becomes more complex with increasing depth. (4) Under the influence of soil texture and water, loose soil fills the bottom of the ground fissure, thus affecting the underground 3D morphology. [ABSTRACT FROM AUTHOR]

Marine terraces are geomorphic markers largely used to estimate past sea-level positions and surface deformation rates in studies focused on climate and tectonic processes worldwide. This paper aims to investigate the role of tectonic processes in the late Quaternary evolution of the coastal landscape of the broader Neapolis area by assessing long-term vertical deformation rates. To document and estimate coastal uplift, marine terraces are used in conjunction with Optically Stimulated Luminescence (OSL) dating and correlation to late Quaternary eustatic sea-level variations. The study area is located in SE Peloponnese in a tectonically active region. Geodynamic processes in the area are related to the active subduction of the African lithosphere beneath the Eurasian plate. A series of 10 well preserved uplifted marine terraces with inner edges ranging in elevation from 8 ± 2 m to 192 ± 2 m above m.s.l. have been documented, indicating a significant coastal uplift of the study area. Marine terraces have been identified and mapped using topographic maps (at a scale of 1:5000), aerial photographs, and a 2 m resolution Digital Elevation Model (DEM), supported by extensive field observations. OSL dating of selected samples from two of the terraces allowed us to correlate them with late Pleistocene Marine Isotope Stage (MIS) sea-level highstands and to estimate the long-term uplift rate. Based on the findings of the above approach, a long-term uplift rate of 0.36 ± 0.11 mm a−1 over the last 401 ± 10 ka has been suggested for the study area. The spatially uniform uplift of the broader Neapolis area is driven by the active subduction of the African lithosphere beneath the Eurasian plate since the study area is situated very close (~90 km) to the active margin of the Hellenic subduction zone. [ABSTRACT FROM AUTHOR]