3D physics-based seismic shaking scenarios for city of Zagreb, Capital of Croatia

In this work, we assess ground shaking in the wider Zagreb area by computing simulated seismograms at regional distances. For the purposes of the simulations, we assemble the 3D velocity and density model and test its performance. First, we compare the low-frequency simulations obtained using deterministic method for both new 3D model and a simple 1D model. We then continue the performance test by computing the full broadband seismo- grams. To do that, we apply the hybrid technique in which the low frequency (f<1 Hz) and high frequency (f=1–10 Hz) seismograms are obtained separately using deterministic and stochastic method, respectively, and then reconciled into a single time series. We apply this method to the MW=5.3 event and four smaller (3.0<MW<5.0) events that occurred in the studied region. We compare simulated data with the recorded seismograms and vali- date our results by calculating the goodness of fit score for peak ground velocity and shak- ing duration. Next, to improve the understanding of the strong ground motion in this area, we simulate seismic shaking scenarios for the 1880, MW = 6.2 earthquake. From computed low-frequency waveforms, we generate shakemaps and compare the ground-motion fea- tures of the two possible sources of this event, Kašina fault and North Medvednica fault. We conduct a preliminary study to determine which fault is a more probable source of the 1880 historic event by comparing the peak ground velocities and Arias intensity with the observed intensities.

Croatian Science Foundation under the Project No. IP-2020-02-3960
European Commission, H2020 Excel- lence Science [ChEESE (Grant No. 823844)]