###### Abstract  
This paper discusses a new method for determining co-seismic displacement using the Global Navigation Satellite System (GNSS) for the precise detection of positional changes at permanent stations after an earthquake. Positioning by the Precise Point Positioning (PPP) method is undertaken using data from the GNSS satellites and one designated station. A time series is processed by an anharmonic analysis before and after an earthquake and these one-day solutions increase the accuracy of measurements. The co-seismic static displacement can be precisely detected from the analysed time series before and after the earthquake, which can be used for the verification of seismic models. Reliability of the estimation of the size of the co-seismic offset is given by the mean square error (RMSE) of the shift. In this study, RMSE was determined by two approaches, initially from variances within PPP processing, and secondly when no positional change from the GNSS before or after the earthquake was assumed. The variance of the data in the time series gives a more realistic estimate of RMSE. This dual approach can affect seismological interpretation due to the need for the interpreting geophysicists to determine which case of co-seismic displacement is more probable for any given locality. The second approach has been shown to provide a more realistic co-seismic displacement accuracy in this study. permanent GNSS stations; Precise Point Positioning processing; anharmonic analysis; co-seismic displacement 2021  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON] An Innovative Approach to Accuracy of Co-Seismic Surface Displacement Detection Using Satellite GNSS Technology  
2021  
11280  
methods using double integration of acceleration records. However, even contemporary attempts of this kind [4] are difficult due to low-frequency natural and instrumental noise. The advent of space-geodesy techniques at the end of 20 th century in the form of Global Navigation Satellite Systems (GNSS), has considerably improved the off-fault measurement of earthquake-related displacements (co-seismic dynamic and static displacement, and post-seismic displacement). A study of a 20-year database of co-seismic displacements in Greece has been discussed by [PERSON] et al. [5]. Further progress has been provided by the introduction of In-SAR methods [6] whose main advantage is a dense (periodically every 6-12 days) sampling of the motion on the Earth's surface over a large area [7,8]. In-SAR methods can also detect pre-seismic ground deformation, as demonstrated by [PERSON] [9]. It is our view that In-SAR methods will be used more frequently in the future. Other possibilities also may become apparent, especially in the field of earthquake prediction, when monitoring electromagnetic extra-low-frequency perturbations [10]. At this time, there is a very cooperative atmosphere in the field of seismology and space geodesy, especially within investigations of larger earthquakes (magnitude >-5), and in particular studies of slip evolution and distribution on faults. It is expected that future progress in this field will mainly be focussed on the continuous monitoring of known faults or broader areas. This will lead to better understanding of co-seismic processes, and post-seismic relaxation, or even a possible pre-seismic \"earthquake preparatory phase\". Seismic and geodetic measurements can contribute to a better understanding of the rheological properties of fault zones (and their laws of friction), which remain enigmatic, hampering earthquake predictions, which is discussed in more detail by [PERSON] et al. [11,12]. The aim of this study is to determine the co-seismic displacement from a time series of coordinates determined by the PPP GNSS method and a realistic estimate of the accuracy for this co-seismic displacement. This estimate of accuracy evaluates the statistical significance of the determined displacement.