Combined Space–Time Analysis of Geodetic and Geological Surveys for Evaluation of the Reliability of the Position of Points in the Geodynamic Network of the City of Zagreb

Abstract

This paper describes the long-standing interdisciplinary geodynamic research for the wider Zagreb area, the most seismically active area of the continental part of the Republic of Croatia, extending over an area of around 800 km2. As a result of the research, which is based on geodetic and geological field measurements, a unique interdisciplinary movement model of the surface layers of the Earth’s crust for the project area is created. The analysis of survey data has determined the continuous tectonic activity of the wider Zagreb area. In the past 18 years, a total of 10 GPS measurement campaigns have been conducted. For each campaign, the velocities of geodynamic network points were calculated, and the cumulative velocity rate was determined from all measurement campaigns for the entire period of observations using GAMIT/GLOBK software. Displacements at individual measuring points of the network, throughout research, vary widely and depend on its location within the local geologic structural framework and regional tectonic movements. These displacements in detail represent a measurable insight into the tectonic activity of the area of research. Therefore, in this paper, special attention is given to the analysis and explanation of these variations in the displacements of the individual geodynamic points, even indicating the questionable quality of location selection for some points. In this way, we seek to explain the causes and mechanisms of such displacements. The results presented in this paper represent the preseismic area condition and further can be used in coseismic 2020 earthquake displacement analysis.