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.

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 (S_a) 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 S_a 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.

The HOMEROS project advances multi-hazard assessment through the integrated use of seismological and geodetic infrastructures within an Open Science framework. This paper presents the seismological and GNSS-based geodetic networks, data products, and processing workflows that underpin hazard monitoring and analysis in tectonically active regions of Greece, with emphasis on the central Ionian Islands and the western Gulf of Corinth. Dense permanent seismic networks provide high-resolution waveform data enabling precise earthquake detection, relocation, and source characterization. Complementary GNSS infrastructures, such as the Hermes network and GL-NKUA cGNSS, deliver continuous observations processed using Precise Point Positioning and kinematic techniques to quantify crustal deformation displacements, and atmospheric parameters. Integrated quality control, standardized processing pipelines, and interoperability through EPOS, EIDA, and institutional repositories ensure compliance with FAIR data principles. The combined seismological and geodetic datasets support advanced applications, including high-accuracy earthquake catalogues, deformation monitoring, and physics-based ground motion simulations for seismic hazard assessment, demonstrated through seismic crises in the study areas. By harmonizing heterogeneous observations and products, HOMEROS enhances reproducibility, data reuse, and collaborative research, providing a robust testbed for multi-hazard assessment in Greece and a transferable model for the broader European and global research community.

Boeotia, located in Central Greece, experiences frequent seismic activity, mainly due to its proximity to the Gulf of Corinth. Significant earthquakes have occurred in the broader study area, such as the ones of Atalanti (M _w = 6.8, 6.9) in 1894, as well as the Alkyonides sequence in 1981 that included three M _w > 6.0 events. In late 2020, a M _w = 4.6 mainshock took place near Thiva, a populated town in Boeotia, followed by the 2021–2022 seismic sequence with three M _w > 4.0 earthquakes. The objective of this study is to perform a Probabilistic Seismic Hazard Assessment (PSHA) for Boeotia through the computation of the Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) using two truncation levels (ε = 0 and 3). Moreover, Uniform Hazard Spectra (UHS) are constructed in terms of Spectral acceleration (S _a ) for Thiva and Livadia, the capital of Boeotia. To achieve this, three seismotectonic models in the form of area sources are employed in the computational framework. Ground Motion Prediction Equations (GMPEs), using data of the area of Greece, are utilized to estimate PGA and PGV. For each area source, the percentages of normal and non-normal (reverse or strike-slip) fault plane solutions are computed in order to generate minor branches for each GMPE that takes into account the focal mechanism type. This approach introduces variability and reduces uncertainties in PSHA. Additionally, a sensitivity analysis was performed by keeping constant one logic tree, first the GMPE, then the source-model tree, while varying the other, to assess the consistency of individual GMPEs and source models. The findings reveal that western and eastern Boeotia have higher seismic hazard, attributed to the seismotectonics of the study area. Additionally, the seismic hazard level in Thiva is higher compared to Livadia.