# Destructive M6.2 Petrinja Earthquake (Croatia) in 2020--Preliminary Multidisciplinary Research
## 7 Estimation of _PGA_ and Response Spectra of the M6.2 Petrinja 2020 Earthquake
Figure 12: USGS Shake Map analysis: (**a**) The peak ground acceleration map and (**b**) GMPE peak ground acceleration predictions (thick purple line) and observations (seismic stations—blue triangles, Did You Feel It DYFI—coloured circles) in consideration of local site effects [59]. Figure 13: Estimation of the distance scaling _PGA_ for rock (\(V_{S30}=800\) m/s) based on (**a**) available Croatian attenuation relations HMI02 and MHH102, (**b**) GMPEs from ASB14 that were derived for Pan-European sites and NGA14 (NGA West-2 GMPEs) from BSSA14 and CY14 (with weights of 0.5 for each), and (**c**) Random Vibration Theory models that were derived by Bora14 for the RESORCE-2012 database and RVT-Sk20 for the BSHAP database. Destructive earthquakes that occurred in the last three decades (Nepal, 2015; Christchurch, 2011; Chile, 2010; Sichuan, 2008; Kocaeli, 1999; Kobe, 1995; Northridge, 1994; Loma Prieta, 1989; Mexico City, 1985) proved that the effect of local soil conditions on the earthquake damage distribution was substantial compared to travel path effects and the effects that were induced by the proximity of earthquake sources. The site amplification factor can be estimated using predefined linear and nonlinear site amplification components that have been utilized in ground motion models (GMPEs) for shallow crustal and active tectonic regions (e.g., global NGA-West 1 and West 2 GMPEs, RESORCE models) as functions of the reference rock _PGA\({}_{rock}\)_ and site _V\({}_{S30}\)_. These models are included in the ASB14, BSSA14 and CY14 models. Bara14 did not include nonlinear amplification and neither did the Sk20 model; hence, their models showed only linear amplification with In(_V\({}_{S30}\)_) in their formulations. Based on the available _V\({}_{S30}\)_ map [69] that was derived on a topographic slope ([70], Figure 14), close and wider epicentral areas varied between two site categories, namely B (360-800 m/s) and C (180-360 m/s), based on the Eurocode 8 categories. Both Croatian attenuation relations, HMI01 and MHH102, only derive reference rock _PGA_ values. In Figure 15, we compare EC8-Type 1 (the importance factor is 1.0 for ordinary buildings) response spectra for 95, 475 and 1000 year return periods with ASB14 and NGA14 response spectra (5% of the critical damping) and with RVT response spectra from Bora14 and Sk20 for three site categories, namely C (300 m/s), B (500 m/s) and A (800 m/s), at close distances of 1 km, 5 km and 10 km from the epicentre. Figure 14: Available _V\({}_{S30}\)_ map that is based on topographic slope [69]. The red star represents the location of the M6.2 Petrinja 2020 earthquake (_M\({}_{w}\)_ 6.4 by USGS). The orange circle represents a 10 km distance from the epicentre. From the response spectra comparisons that are shown in Figure 15, for epicentral distances of close to 5 km, both GMPE spectra are within the 1000 yrp EC8 spectra for A, B and C sites, whereas at a distance of 10 km, the response spectra match the 475 yrp EC8 spectra only for A and B sites. For soft site category C, the GMPE spectra are between 1000 yrp and 475 yrp with a period lengthening (frequency shortening), thereby indicating soil nonlinearity, especially for the periods between 0.1-0.4 s. The RVT-based response spectra show significantly higher spectral accelerations in comparison to the GMPE and EC8 spectra in the mid-to-long period range with similar behaviour within 1000 yrp and 475 yrp. However, for site category C, the EC8 spectra heavily underestimate the RVT spectra. This is the effect of linear amplification (a function of only V530) in the RVT models compared to nonlinear amplification (a function of V530 and PGA\({}_{\text{rock}}\)) in the GMPE models. The PGA distance attenuation that is shown in Figure 13 for rock sites (800 m/s) can be compared with the spectral accelerations at the zero period within various sites (300 m/s, 500 m/s and 800 m/s).