1st Croatian Conference on Earthquake Engineering 1CroCEE 2021

CROPOS (Croatian Positioning System) is a Croatian permanent GNSS (Global Navigation Satellite System) network featuring 33 stations distributed over the national territory at an average distance of 70 km between stations. The system was established in 2008, in the meantime enlarged and improved, and eventually, in summer 2019 it was upgraded to support observations of the European Galileo satellite system (in addition to previously supported GPS and GLONASS systems). Within the project of CROPOS’s upgrade co-funded by the EU (European Union), all permanent GNSS stations were equipped with the newest Trimble Alloy receivers and Trimble Zephyr 3 Geodetic antennas, whereas the software of the control center (Trimble Pivot Platform) was upgraded to a newer version. One of the CROPOS’s stations (ZAGR) is located (more precisely its antenna) on the roof of the building where three faculties of the University of Zagreb (Geodesy, Civil Engineering, Architecture) are headquartered. For the first time, the effects of the M5.5 Zagreb earthquake, combined surface and building motion, have been identified and assessed by the GNSS method supported by E5, E5a, E5b, and E5AltBOC signals of Galileo satellites. By analysis of 1 Hz processing results, the effects of the earthquake being far above the noise level, have been discerned leading to the assessment of kinematic behaviour of the station caused by M5.5 earthquake. ZAGR station at the approx. 9 km distance from the estimated epicentre, have shown movements in the range of approx. 13 cm in direction N-S and approx. 6 cm in direction E-W, whereas some movements in the vertical direction were identified to be slightly above the noise level. Although the kinematic behaviour was pronounced, there haven't been revealed permanent displacements as a consequence of M5.5 earthquake. One second (1 Hz) resolution results have enabled a thorough analysis of the kinematic behaviour of ZAGR station and potential of the GNSS method.