A major study project in the field of earthquake geology was recently concluded, focused on the area affected by the 2020 Petrinja earthquake and the capital region Zagreb. The project saw collaboration between experts from the National Institute of Geophysics and Volcanology (INGV) and researchers from the Croatian Geological Survey (CGS-HGI) based in Zagreb, by virtue of the Memorandum of Understanding stipulated between the two entities in December 2021.
The study was an integral part of a large multidisciplinary project, which brought together geological, geomorphological, geophysical and paleoseismological expertise
The primary objective was to contribute to the characterization of the seismic behavior of the Petrinja fault and neighboring faults, as well as the evaluation of the possibility of iintegrate national studies on seismic hazard with data on active faults and coseismic effects on the physical environment.
The research developed along three main lines: the identification and mapping of the major potentially seismogenic active faults in the region, the study of the seismic history of the Petrinja fault and the revisiting of the liquefaction sites of 2020 for the characterization of the territory.
With the financial support ofItalian Embassy in Zagreb, committed to promoting the bilateral cooperation between Italy and Croatia in all sectors, including scientific and research work, the results of this collaboration have been presented in important national and international conferences and are being published in renowned scientific journals, as well as through a dedicated geographical portal.
Recently, the Faculty of Sciences of the University of Zagreb hosted a day of presentation of the research conducted by scientists from INGV and CGS-HGI, entitled: "Earthquake geology studies in central Croatia: active faults and seismogenic potential " . During this event, Italian and Croatian scientists illustrated to the academic and general public the activities and first results of two years of intense collaboration.
The results presented include the first maps of active faults in the Petrinja area, the first paleoseismological studies in Croatia and the database of liquefactions produced by the 2020 earthquake. Furthermore, a publication describing the project and the results obtained was distributed.
The collaboration of the group of European scientists will continue with the common goal of deepening the knowledge acquired on the seismogenic characteristics of the Petrinja region and extending research in the field of earthquake geology to adjacent areas.
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Photo - The paleoseismological excavation campaign for the identification and dating in the geological record of earthquakes that occurred in the past along the Petrinja fault was conducted as part of the collaboration of a group of European scientists between 2021-2023.
picture 1 - Example of a photomosaic of a paleoseismological trench wall. The yellow lines highlight the main stratigraphic contacts while the red lines highlight the faults that have strongly deformed the deposits and some of which were activated during the 2020 earthquake. The latter coincide on the surface with some fractures and a flexure zone.
Photo 2 - View of an open paleoseismological trench wall across the Petrinja fault. The wall is cleaned and made regular and leveled through a grid of 1mx1m boxes (red cords), so as to be able to record and study stratigraphy and tectonics and define events and dislocations. In this trench, an abandoned river channel (the base of which is highlighted by yellow flags) sitting on top of a gray clay appears repeatedly displaced across the fault zone (red-orange flags).
Picture 2 - One of the most obvious coseismic effects of the Petrigna earthquake on the natural environment was liquefaction. This phenomenon is commonly produced in alluvial and coastal plains where surface aquifers contained in sandy sediments become overpressured as seismic waves pass, causing water and sediment to escape to the surface and at the same time cause soil subsidence. In 2020, liquefaction was observed over an area of more than 2000 km2. The liquefaction sites were surveyed, cataloged and characterized by the group of European scientists and all data were reanalyzed and systematized in a geographic database during the INGV-HGI project. In the map, the orange dots represent the liquefaction points detected in detail while the yellow lines show the liquefaction bands observed remotely (drone or satellite images).