The GNSS velocity field of central Greece and the Peloponnese

SUMMARY We present a comprehensive dataset of 920 coordinates and 509 velocities for geodetic points in central Greece and the Peloponnese, an area characterised by intense tectonic deformation. The points, with observation periods within the 1990–2024 range, are organised into three categories: permanent stations, triangulation pillars, and markers. The latter two categories are subdivided according to whether or not they feature self-centring. Most of the triangulation pillars belong to the Greek national network originally surveyed in the 1960s–70s. The GNSS data were processed using the GIPSY 6.4 software. To assess the secular velocities, we corrected for co-seismic and post-seismic displacements using earthquake parameters constrained by the time series of the permanent stations. Self-centring systems improve precision, reducing the average horizontal coordinate residual variability from 6.15 to 4.45 mm. The velocity uncertainties stabilise below 0.15 mm yr−1 when the time series exceed twenty years. Points with self-centring achieve 0.2 mm yr−1 accuracy after twelve years of data, compared to twenty years for those without self-centring. After twenty-five years, campaign points observed eight to ten times match the precision of permanent stations. The velocities at the campaign points further validate the HELVEL model previously developed using permanent stations only. We calculate a seven-parameter transformation from the original coordinates of 424 triangulation pillars to their GNSS-based ITRF2020 coordinates at epoch 2020.0. The lowest mean scatter after the transformation is 0.134 m when 1965 is used as the mean epoch for the triangulation data. We then apply this transformation to all 9,729 pillars of the study area. At the 424 resurveyed pillars, the GNSS ellipsoidal heights agree with the sum of the levelled heights and the official HG2023 geoid heights to within 0.184 m root-mean-square. Our dataset is entirely referenced to ITRF2020 at epoch 2020.0, which enables interoperability with previous and future geodetic studies. Dense campaign point arrays are critical for resolving the strain distribution at the scale of individual active faults, beyond the reach of arrays of permanent stations alone.