Comparison of geodetic and seismic strain rates in Greece by using a uniform processing approach to campaign GPS measurements over the interval 1994-2000

In this study we rigorously combine 18 old campaign GPS data sets from Greece covering the period 1994-2000. Although the majority of these old datasets have been analyzed and reported previously, it has not been possible to combine them into a single velocity field and apply strain analysis. Here a uniform, final coordinate solution is given by reprocessing 43 global, long-running International GNSS Service (IGS) sites together with 280 local sites. The 221 daily SINEX files are then combined in a least squares approach and the geodetic horizontal velocity field in ITRF2000 and Europe-fixed reference frame is derived. Two methods are used to compute the geodetic strain rates: (i) discrete estimates within contiguous polygons, and (ii) a continuous curvature surface fitted to the velocity field. The seismic hazard potential can be determined by comparing the geodetic and seismic strain rates. The published 300 year earthquake catalogue best describes the major active tectonic features at the scale of geodetic strain determination. The geodetic strain appears larger than the seismic strain for the majority of the region, suggesting that accumulated strain has not yet been released by earthquakes. The geodetic field is consistent with the detailed constraints implied by the observed orientations of faulting as these are given in the 300-year catalogue. We have shown that with the GPS dataset used in this work and following this processing scheme reasonable results can be obtained comparable with more recent studies, CGPS data and by recent earthquake activity.