The main purpose of this research is to develop a real-time GPS monitoring system with the aid of a Kalman Filter for use in an active tectonic region near Istanbul, and its surrounding region. Currently, an ongoing project exists, funded by the World Bank, that monitors deformation in Istanbul and the Marmara Region. Istanbul is one of the largest cities in the world, and is under possible earthquake threat. In order to set up a powerful control system, a surveying and estimation method was designed and the necessary software, called RT-MODS2 (Real-Time Monitoring Of Dynamic Systems 2), was developed. The software reads real-time input data from GPS receivers and performs deformation analyses with the help of the Kalman Filter. Some studies of filtering and deformation analysis were performed in order to detect failures and outliers, and to increase the reliability of the deformation analysis.