Three days before the earthquake in Skopje there was a compression of the Earth’s crust

Abstract

In this paper are analysed daily changes of all distances between four MAKPOS GNSS referent stations (Skopje, Tetovo, Kumanovo and Veles). In that way are defined the deformations of the Earth’s crust in wide area of Skopje from 20th of August 2016 till 20th of September 2016. It was noticed that three days before the earthquake from 11th of September 2016, there was decreasing of the site distances between MAKPOS GNSS stations in Skopje surrounding, practically there was compression of the Earth’s crust around Skopje. On 11th of September 2016 there were several smaller earthquakes, all of them were with epicentres nearby Skopje. The most powerful earthquake was with magnitude 5.2 degrees per Richter and its hypocentre was at a depth of 4 km. We decide to analyse in more detail whether was any decreasing of the site distances between MAKPOS GNSS stations before 20th of August 2016 and for that was analysed time period from the beginning of 2016 till 30th October same year. We found that prior to all earthquakes, even those smaller before and after the main earthquake there was always decreasing of the site distances between GNSS referent stations and that the earthquake appeared two to nine days after the compression. With analyse of the earthquake in Kraljevo (Serbia) from 2010, also we get that tree days before earthquake there was decreasing of the site distances between GNSS referent stations. With analyse of the earthquake in Drežnica (Croatia) from 2013 was obtained such a result. Drežnica earthquake was on reversal fault, and Kraljevo and Skopje earthquakes were on normal faults.