# Destructive M6.2 Petrinja Earthquake (Croatia) in 2020--Preliminary Multidisciplinary Research
## 8 Discussion
Additionally, this range of \(PGA_{site}\) can be compared to the value for the Ston-Slano 1996 M6 earthquake: It was recorded as a _PGA_site of 0.64 g at the acceleration station in the Ston saltern, where the total thickness of the sedimentary cover (intermediate to high plasticity clay in the first 15 m) over the bedrock was between 35-50 m. The observed amplification was between 3.8 and 5.0, as reported by [PERSON] et al. [74], for _PGA_rock estimates of between 0.128 and 0.170 g at an epicentral distance of 16 km. Therefore, the design value of _PGA_ of approximately 0.3 g was exceeded in the Petrinja epicentral area, as evidenced by the very heavy damage or collapse of simple unreinforced masonry (regular) buildings. Since there was no accelerograph close to the epicentral area to register the mainshock, estimated _PGA_rock/site values and corresponding spectra cannot be compared with the M6.2 Petrinja acceleration recordings, which would certainly show various types of nonlinear soil behaviour ranging from traditional high-frequency deamplification (period lengthening) to liquefaction [71]. [PERSON] and [PERSON] [75] showed that high plasticity clays are more flexible than less plastic soils, thereby substantially amplifying ground shaking, as was observed in Mexico City in 1985. Moreover, according to these authors, large amplifications could occur due to the linear strain characteristics of soft clay deposits around the world. Since this study is only preliminary, the sizes of local site amplifications and the induced nonlinearity must be examined with site response modelling from subsurface profiles that will be collected from various geotechnical site characterization investigations in the Petrinja area and in NW Croatia. We must investigate the relationship between the surface lithology in the upper 10 and 20 m and deeper geophysical profiles beyond 30 m depth to investigate site response issues that are related to near-source effects. At larger distances (>20 km) and with _PGA_ attenuation, the resulting _PGA_site was certainly affected by local site amplification, primarily by the Sava Basin and Hrvatsko Zagorje Basin. This assumption corresponds with the macroseismic intensity map that is shown in Figure 3 and with the reported damage in NW Croatia at larger distances (>50 km). Thus, future studies of site response modelling and GMPE testing in terms of estimated site amplifications and PGAs should be compared with recorded strong motions and their response spectra from accelerometric stations. This event, together with its two strong foreshocks and particularly after a new mobile accelerometric network, was installed to capture all aftershock data and produced an impressive amount of data that remain to be analysed. Empirical response spectra from strong motion data in the epicentre vicinity would certainly determine the selection of suitable GMPE candidates. The assignment of the vulnerability class (or selection of fragility function) has a strong influence on the damage prediction [76; 77]. A simple (most likely) assignment of the vulnerability class ignoring the subsoil conditions leads to lower damage grades for low intensities and higher damage grades for high intensities in comparison to more engineered approaches. Therefore, realistic and reliable risk scenarios for master plans need a broad database to allocate empirical vulnerability and/or analytical fragility functions for the damage assessment. In any case, the engineer-assigned (most probable) vulnerability or building type-specific fragility function has to consider the uncertainty in building response characteristics and the particularities of local construction practice. Thus, building response measurements from various representatives of similar building types help to provide input parameters for the calibration and verification of reliable structural models and derivation fragility functions considering local construction practice.