Seismotectonic implications for the Peloponnese (SW Greece) region based on geodetic crustal deformation analysis

Peloponnese is a seismotectonically active region in Greece (Eastern Mediterranean) located just north of the Hellenic Subduction Zone, along which the Aegean and Nubian continental plates converge, and south of the Corinth Gulf, a rapidly extending rift. In addition to these highly tectonically active margins, the crust of the Peloponnese is undergoing deformation, which has locally generated significant earthquakes. In this paper, an upper crustal deformation analysis has been performed in order to comprehend i) how much and under which mechanism this region is deforming, ii) whether our results can explain the past seismicity, and iii) whether areas of low recorded seismic activity till recently are prone to a possible future increase of activity, a vital piece of information in terms of seismic hazard assessment. This analysis was based on primary geodetic raw data, collected by 32 permanent GPS/GNSS stations, which monitor the wider Peloponnese region. Considering these measurements, the geodetic strain parameters were estimated by implementing triangulation and interpolation methodologies, providing the qualitative and quantitative deformation properties of Peloponnese. The results show a wide-spread low deformation, mostly shear, with local highs in areas where seismic activity is evident; the 2008 Andravida earthquake is a typical example, as it is related to a right-lateral blind strike-slip fault. However, normal faulting with a dip-slip component also contributes to upper-crustal deformation in the study area, as demonstrated by seismic events such as the Sparta and Kalamata earthquakes. These results suggest that several seismically ‘quiet’ regions of Peloponnese (such as the eastern-northeastern part) show significant deformation, since the accumulated strain in these regions appears not to be released by smaller frequent events; therefore, they might have the potential of hosting moderate to strong earthquakes along localized zones of deformation in the future, indicated as areas with recorded higher strains.