**1. Introduction**

Today, large distances and compressions of terrain can be measured very precisely using satellites of the GNSS (global navigation satellite system). GNSS consists of GPS (American), GLONASS (Russian), GALILEO (European), and COMPAS (Chinese). GPS (global positioning system) satellites orbit the Earth at an altitude of 20,200 km from the Earth's surface in six orbital planes, so that the GPS receiver on Earth can always receive signals from at least four satellites.

Satellites send signals to Earth, which contain the time of the satellite's atomic clock at the moment the signal is sent from the satellite. The receiver on the Earth's surface records the arrival time of the antenna signal according to its electronic clock. The satellite distance is calculated based on the difference in the time of transmission and the reception of the signal. In a similar way, satellite coordinates are measured from stations on the Earth's surface whose coordinates have previously been established. To make the calculation easier, a positioning system on the Earth's surface was installed in Macedonia. For this purpose, a system of permanent reference stations called MAKPOS (English abbreviation for Macedonian positional system) was set up in North Macedonia to determine the position of points on the ground. Similar

terrestrial positioning systems have also been developed in Croatia (CROPOS), Slovenia (SIGNAL), Serbia (AGROS), Montenegro (MONTEPOS), and Bosnia and Herzegovina (BHPOS and RSPOS) [1, 2].

In order to measure compression in the Earth's crust, four reference stations near the epicenter of the earthquake are selected and measured by GNSS satellites 24 hours a day for several days before and after the earthquake. If almost all the distances are shortened in 1 day, compression has occurred in the Earth's crust, after which an earthquake occurs 3 or 2 days later. In 2016, an earthquake occurred in Skopje, 3 days after compression, while the aforementioned earthquakes in Kraljevo, Drežnica, and Zagreb occurred after 2 days of compression. This phenomenon can be used to predict earthquakes in the vicinity of the fault under compression.
