Abstract
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.