Structural-geomorphological aspects of the Petrinja earthquake M6.2 (Croatia) - preliminary considerations

A strong earthquake of magnitude 6.2 with the epicentre near the town of Petrinja occurred on December 29th, 2020 in the fault zone of the right strike-slip Pokupsko Fault in Croatia. The aim of this study was to determine if there are geomorphological indicators of active tectonics in this area. General morphometric methods based on a digital elevation model with a resolution of 10 m were used. Geomorphological indicators of active tectonics were also determined based on topographic maps and hillshade relief. All the collected data were used to reconstruct the traces of the main morpholineaments on the surface and to determine the main morphostructures. It was found that the central part of the studied area, Hrastovička Gora, has morphological features possibly corresponding to a pop-up structure (positive flower) and that it consists of two separate morphostructures. They are separated from each other by an east-west oriented morpholineament, which is a possible segment of the Pokupsko Fault. Comparison of the collected results with the data on the location of the epicentres of the Petrinja series earthquakes of magnitude 4.0 and higher, which occurred in the period from December 28th, 2020 to March 3rd, 2021, indicates the possibility that these earthquakes were related to this restraining bending zone of the right horizontal Pokupsko Fault, which should be studied in more detail in the future.