## Analysis of the GPS Data  
Forty homogenously distributed IGS points and their four-year solution time series provided by the Jet Propulsion Laboratory (JPL) for the period 2012 through 2016 were used (Figure 1). For this, we referred to the National Aeronautics and Space Administration (NASA)-JPL official website ([[http://sideshow.jpl.nasa.gov/post/series](http://sideshow.jpl.nasa.gov/post/series)]([http://sideshow.jpl.nasa.gov/post/series](http://sideshow.jpl.nasa.gov/post/series))). Position time series for each IGS station concerning local topocentric coordinates north, east, and up (n, e, and u) and accompanying standard errors were downloaded.  
First, the JPL continuous time series constituting daily position estimates were decimated into monthly sampled GPS campaign time series by picking only one position estimate (i.e., day fifteen here) from each month of the year. In practice, this means that the field operator occupies the geodetic survey point with a GPS receiver every month in a year. This might be considered an ideal survey procedure, which is much denser than the one measurement per year. Obviously this would be much more cumbersome than the traditional field work in which the geodetic mark is visited for a couple of consecutive days each year [1]. Considering this we worked on an alternative survey procedure in which the sampling is made selecting one position estimate (i.e., derived from full 24 h) every  
Figure 1: Locations of the International GNSS Service (IGS) stations used in this study.  
four months. This is surely superior to the sampling; one measurement per year with 8-10 h of observation session.  
Secondly, we estimated the deformation rate from a four-year continuous JPL time series. [PERSON] and [PERSON] (1975) and [PERSON], [PERSON], [PERSON], [PERSON] (2015) assess the minimum span of continuous GPS time series for the appropriate determination of the deformation rate. They recommend a minimum span for deformation monitoring of between 2.5 and 4.5 years. Figure 2 shows GOLD continuous, monthly, and four-monthly decimated campaign time series.  
Furthermore, to take into account the antenna set up error, we added some biases to the coordinate components north, east, and up. As noted earlier on, we generated synthetic GPS campaigns using the data of IGS continuously operating stations where the antennas are usually on top of concrete pillars and their position does not change over time. However, campaign GPS measurements are usually collected by mounting the GPS antenna on top of a tripod while visiting the survey sites. This would create an error due to possible improper centering and incorrect measurement of the antenna height. Considering the antenna set up error would be randomly distributed over a long time period, it was generated synthetically as a random noise produced from a MATLAB routine. On the magnitude of the bias we referred to [PERSON] (2016) and [PERSON], [PERSON] (2017) who assesses the antenna set-up errors. The bias is noted to be 1-3 mm from the setup of tripod mounted GPS antennas using optical plummets. Therefore we generated white noise with the standard deviation of 3 mm. The best way to assess this would be taking campaign measurements near to (\(<\)10 m) continuous stations however we would not be able to produce our results globally.