The 2nd Geomagnetic Information Renewal Cycle started in 2017, pursuant to a request from the State Geodetic Administration and Ministry of Defence to ensure actual declination and its annual variation across the territory of Republic of Croatia. A test survey was performed at POKUpsko as part of the project in 2017. The PRM1 Primary Repeat Station had been destroyed, and the survey performed at a secondary location established in 2011, which subsequently became the primary location, known as PRM2. In this paper, the results of 2017 measurements reductions are presented, along with reductions in PRM1 and PRM2 measurements in 2011, and differences between the PRM1 and PRM2 locations, which are necessary to maintain the continuity of measurements at Pokupsko.

Over the years, Global Navigation Satellite Systems (GNSS) have been established in the geosciences as a tool that determines the positions of discrete points (stations) on the Earth’s surface, on global to local spatial scales in a very simple and economical manner. Coordinates obtained by space geodetic measurements ought to be processed, adjusted, and propagated in a given reference frame. As points on the Earth’s surface do not have a fixed position, but rather, are moving with associated velocities, it is inevitable to include those velocities in the coordinate transformation procedure. Station velocities can be obtained from kinematic models of tectonic plate motions. The development and realization of an all-in-one standalone desktop application is presented in this paper. The application unifies coordinate transformation between different realizations (reference frames) of the International Terrestrial Reference System (ITRS) and European Terrestrial Reference System 1989 (ETRS89) following European Reference Frame Technical Note (EUREF TN) recommendations with temporal shifts of discrete points on the Earth’s surface caused by plate tectonics by integrating no-net rotation (NNR) kinematic models of the Eurasian tectonic plate.

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The Adriatic microplate has always attracted scientific attention, and various studies on the geodynamics of this area have been performed over the years. With the development of global navigation satellite system (GNSS) technology in the last 30 years, most significant research in this field has used it as the primary source of data on geodynamic movements. However, apart from a few global positioning system (GPS) campaigns conducted in the 1990s, the measurements had a low spatiotemporal density. Therefore, the eastern side of the Adria region or the territory of the Republic of Croatia was usually omitted from the results presented in the various published papers. A study of this literature concluded that the territory of Croatia represents a kind of scientific gap and that denser measurement data from GPS/GNSS stations could be used to supplement the geodynamic picture of the area in question. Thus, GPS/GNSS measurements from 83 stations (geodynamic, reference, and POS’ GPS/GNSS) all over Croatia and neighboring countries for a period of almost 20 years (1994–2013) were collected and processed with Bernese software to obtain a unique database of relative velocities. From the geological perspective, the most important and latest insights on the recent geological structural setting, tectonic movements, most active faults, and relationships and movements of structures were taken into account. It was important to compare the geodetic and geological data, observe the present tectonic dynamics of the geological structural setting, and determine the causes of the obtained directions of movement. The research presented in this paper, based on a combination of geodetic and geological data, was conducted to broaden the current knowledge of the present tectonic dynamics of the geological structural setting of the eastern part of the Adriatic region.

<p>The status of the Croatian Geomagnetic Repeat Stations Network (CGRSN) and Croatian Geomagnetic Network for Field Mapping (CGNFM), completed in 2010, was described. Standard and new survey practices as well as reduction techniques were presented. The CGRSN data reduced in reference to the L'Aquila (AQU), Grocka (GCK) and Tihany (THY) observatories using weighted averages were given for the epoch 2008.5. Detailed pictures of Dalmatia's geomagnetic field of 2008.5 and the corresponding anomaly, obtained from the CGNFM data were shown.</p>

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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.

inTroduCTion"Consequences" of Croatia's existence as a part of former Austrian-Hungarian Monarchy (1901) are seen in geodetic aspect as well. Republic of Croatia has historically inherited horizontal (2D) coordinate reference system as colloquially called "HDKS" (cro. Hrvatski državni koordinatni sustav), "Hermannskögel", "HR1901" or "MGI1901". HDKS was realized by astro-geodetic measurements of Military Geodetic Institute (MGI) in 1 st order triangulation network, inhomogenously adjusted in 7 separate blocks ( Figure 1) by conditional measurements . Fundamental point (origin) (P 0 ) of HDKS was situated at Hermannskögel hill, near Vienna (H = 542 m). Coordinates of the origin (ϕ 0 = 48°16´15˝.29, λ 0 = 33°57´41˝.06 from Ferro) and the orientation to the nearby hill Hundesheimer Berg (A = 107°31´41˝.70) were determined by astro-geodetic measurements as well . HDKS represents local (non-geocentric) geodetic datum, defined by 5 parameters: 2 for surface definition (ellipsoid semi-major axis -a; flattening -f) and 3 position parameters (ϕ 0 , λ 0 , h 0 or vertical deflection components -ξ 0 , η 0 with geoid undulation -N 0 ) (Bašić, 2005a). Surface parameters define the mathematical approximation of Earth's shape -ellipsoid. For HDKS Bessel 1841 rotation ellipsoid was selected. Position parameters, defining the fundamental point (origin) are indexed with "0" (zero) because its initial values must be a priori known or arbitrarily selected. If arbitrary position parameters are selected, equality follows: ξ 0 = η 0 = N 0 = 0. This equality causes superposition of geodetic and astronomical coordinates (ϕ 0 = Φ 0 ; λ 0 = Λ 0 ) that is superposition of normal and vertical at P 0 . Equality N 0 = 0 causes the superposition of ellipsoidal and orthometric height (h 0 = H 0 ) that is coincidence of ellipsoid and geoid surfaces at P 0 . Above described procedure of absolute orientation of 1 st order triangulation network for local geodetic datum definition is the fundament of astro-geodetic measuring technique (Čubranić, 1972). Transformation to projection plane is ensured using Gauss-Krüger vertical cylindrical projection (adopted in 1924) (Borčić, 1976) with division of the territory of Republic of Croatia in two meridian zones (5 th and 6 th ). Looking from historical point of view to height component as indispensable part of compound coordinate reference system (CCRS), Republic of Croatia has inherited two reference height systems/datums, based on two levelling networks of highest order: Austrian Precise Levelling (cro. Austrijski precizni nivelman -APN) and 1 st High Accuracy Levelling (cro. I. nivelman visoke točnosti -INVT) ( Figure 2).APN was conducted in period from 1874 to 19016 including whole southern and southeastern part of former Austrian-Hungarian Monarchy, that is territories of today's Croatia, Slovenia and Bosnia and Herzegovina (Rožić, 2001). At the 2 nd Conference of Government Commissioners in 1867, APN was suggested to be a basis for height system realization. The holder and contractor was also MGI fr...