**6. Analysis of terrain deformations using daily distance changes in the MAKPOS network before and after the main earthquake, that is, from the 1st of January 2016 to the 30th of October 2016, around Skopje**

In order to investigate whether there was previous compression of the terrain before the main earthquake on September 11, 2016, we analyzed the daily changes in the distance between GNSS stations in the vicinity of Skopje since the beginning of the year (i.e., 7 months before the main earthquake).

#### **Figure 7.**

*We also examined the daily changes in longitude from the beginning of 2016 until the main earthquake. For January 2016, we got the daily length changes shown in Figure 7. We can see that there was one small earthquake in January, which was preceded by a small compression. We can see that the two lengths became longer at the beginning of the year. This is typical for such situations because at that time the distance between the plates was large. After the collision, their direction changes, and they become shorter. When it happens later it is usually a sign that the earthquake will be weak. The same thing happened several other months before the earthquake. Graphs for other months in which minor earthquakes occurred can be found in source [8].*

*The Possibility of Earthquake Forecasting, a Few Days before the Earthquake Using GNSS... DOI: http://dx.doi.org/10.5772/intechopen.108848*

Several minor earthquakes occurred in Macedonia in the vicinity of Skopje on September 11, 2016. The third and largest of them occurred at 15:10 (local time) and had a moderate magnitude of 5.2 on the Richter scale. The epicentre of the earthquake was located at latitude φ = 41.98° and longitude λ = 21.50°, and its hypocentre was at a depth of 4 km. It was felt in Kosovska Mitrovica, Niš, Vranje, and Belgrade.

A similar quadrilateral with diagonals was used in the analysis of earthquakes in Kraljevo [4], Drežnica [5], and Zagreb [7].

We also calculated daily changes in the distance between MAKPOS reference stations in the vicinity of Skopje for the months of February, March, April, May, June, July, August, September, and October of 2016. They are graphically shown in Figures 7–15 in our paper [8].
