PGA vertical estimates for deep soils and deep geological sediments - A case study of Osijek (Croatia)

This paper analyzes vertical PGA strong-motion estimates for the city of Osijek. Osijek serves as a case-study area for low to medium seismicity regions with deep soil and deep geological sediments underneath the local soil. The new regional PGA attenuation equations for vertical ground motion are constructed for this purpose, as are the accompanying seismic micro-zoning maps. The vertical PGA values of different regional real strong motion are compared to the empirical PGA estimates. Finally, vertical to horizontal PGA estimation ratios are computed and examined. The results suggest that the vertical PGA design values for the examined area can be approximated as 0.61 of horizontal PGA values, which is a 37% higher ratio than the one given by Eurocode 8 for Type 2 spectra in 2004. When the recorded data from similar regions increases several-fold compared to what is now available, it will be possible to better calibrate the empirical scaling equations and to produce more credible vertical PGA estimates.