As part of the project ” Investigation of seismically vulnerable areas in Croatia and seismic ground motion assessment – CRONOS”, which was financed (duration until April 30, 2024) from the Norwegian financial mechanism 2014-2021 in the amount of 85% and co-financed with 15% by the Ministry of Regional Development and European Union funds, on September 11, 2024, 2 obsidian accelerographs (Kinemetrics) were installed in Trakošćan Castle and at the Faculty of Geotechnical Engineering in Varaždin. The installation was carried out by collaborators on the CRONOS project, Assoc. Ph.D. Davor Stanko and Bruno Mravlja and Tomislav Fiket from the Seismological Service of the Republic of Croatia, whereby data transfer to CRONOS servers was established.
Considering the attractiveness of the Trakošćan castle, the installation of the accelerograph was covered in the media by the Hrvatska radio televizija: https://magazin.hrt.hr/price-iz-hrvatske/uredaji-za-temeljito-istrazivanje-seizmicnosti-11758857
Through the CRONOS project, an attempt was made to facilitate the development and modernization of earthquake hazard assessment in Croatia, and to acquire knowledge and develop tools, such as updated maps and models, for the development of rules for reducing earthquake hazard. The developed methods are planned to be applied to various seismically active areas, and the collected data will continue to be collected. Sacred buildings and cultural heritage buildings, such as Trakošćan Castle, are particularly attractive. The accelerograph was installed in the heart of the castle, and in addition to the 4 already installed accelerometers (acquired by the Faculty of Geotechnics), it would enable high-quality monitoring of the dynamic behavior of the castle, which can be a good diagnostic tool in the event of an earthquake. Namely, in the event of damage, changes in the basic frequencies of the castle are possible, as was shown by measurements immediately after the Petrinjski earthquake.
With regard to the general geomechanical features that influence seismological measurements, in the narrower area of the Trakošćan locality we find only solid rocks, which include incompletely cemented sedimentary rocks (sandstones and conglomerates), which are categorized by geophysical measurements as category A according to the Eurocode 8 classification. On the other hand, in the area of the Geotechnical Faculty, there are quaternary alluvial deposits (sand and gravel saturated with water), which are categorized by geophysical measurements as category C according to the Eurocode 8 classification. The final benefit of installed accelerographs and the measurement of the acceleration of ground motion due to earthquakes on different types of soil (rock-alluvial deposits) is to determine changes in the characteristics of ground motion due to earthquakes, i.e. realistic amplification of surface ground motion, which ultimately has applications in earthquake-resistant construction or anti-earthquake reconstruction.
Prepared by Davor Stanko and Bruno Mravlja
