## 1 Introduction  
To understand the seismic behaviour and estimate the seismic resistance of historic masonry towers, finite element analyses of the structures are usually performed [1; 2; 3; 4; 5]. The most common difficulties in numerical modelling of such buildings are uncertainties related to design techniques, material properties, boundary conditions, soil-structure interaction, connection with surrounding buildings, if any, etc. For this reason, in the last decade, numerical modelling of the historic masonry tower has been supported by experimental studies of the structural parameters [6; 7; 8; 9; 10; 11]. For this purpose, experimental modal analysis has proved to be indispensable, since the testing of the mechanical properties, i.e., the so-called static tests (e.g., flat-jack test or diagonal compression test) is known to be insufficient. As mentioned earlier, the experimental estimation of modal parameters (natural frequencies, damping, and mode shapes) plays a very important role in evaluating the seismic behaviour of existing buildings. This estimation can be performed through both forced and ambient vibration tests. Forced vibration testing (FVT), also known as experimental modal analysis (EMA), is a technique in which the modal parameters of the structure are determined based on measured vibrations of the structure that are excited by known external forces. In contrast, ambient vibration testing (AMT), or operational modal analysis (OMA), is a technique in which the modal parameters of the structure are determined based on the measured ambient vibrations when the structure is under operating conditions. In civil engineering, OMA is very attractive because the tests are inexpensive, fast, and do not interfere with the normal use of the structure [12]. Lately, it has become the main experimental method for the assessment of the dynamic behaviour of full-scale structures, and it is especially suitable for historic masonry buildings. On 29 December 2020, an earthquake of magnitude M\({}_{\rm w}\) 6.4 occurred in the central region of Croatia, near the town of Petrinja [13; 14]. The intensity of the earthquake was VIII-IX according to the EMS scale. This was the strongest earthquake that had occurred recently in the Croatian region. The maximum ground acceleration at the epicentre of the earthquake was 114% of g, and the maximum ground velocity was 0.813 m/s at a depth of 13.5 km in the hypocenter. It is reported that 50,000 buildings were damaged. One of the reasons for the large number of damaged buildings is certainly that the main earthquake, the day before, was preceded by an earthquake of magnitude M\({}_{\text{w}}\) 5.2. In the period between these two quakes, there were over a hundred weaker earthquakes in the region [13]. Numerous churches and sacral buildings were damaged or destroyed during this earthquake sequence. Usually, these are massive buildings with tall parts and large, awkward openings, making them exposed to large seismic loads. Therefore, the structures of such buildings are particularly vulnerable during an earthquake [13]. One such building is the bell tower of the Church of St. Anthony of Padua in Cuntic, Croatia, which was significantly damaged during this earthquake. In this seismic area, with the epicentre in Pokupsko, a strong earthquake of M\({}_{\text{w}}\) 5.8-6.0 occurred in 1909. Based on the analysis of this earthquake, the famous Croatian geophysicist [PERSON] discovered a discontinuity between the Earth's crust and the mantle (the Mohoroviciic discontinuity) [13]. The main objective of this research is the modal and structural identification of the bell tower in Cuntic, Croatia. The bell tower was damaged during the Petrinja earthquake in such a way that its functionality was compromised, so an evaluation of its seismic resistance is required. Recently, the application of the results of experimental determination of modal parameters with AMT for different buildings has gained importance [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34].