Preliminary seismic microzonation map of the City of Zagreb (Croatia)

The aim of this study was to create a preliminary seismic microzonation map of the administrative area of the City of Zagreb (Croatia). Geophysical measurements collected in the southern and eastern part of Zagreb were used together with geophysical data available for the northern part of the city. Their analysis and comparison with the geological data enabled the distinction of eight areas with homogeneous seismic behavior – HSB zones. Northern and southwestern parts of the city, assigned to HSB zones 1 to 5, are characterized with shallow bedrock and mostly compacted Miocene and Pliocene sediments. Central and southeastern parts of Zagreb, assigned to HSB zones 6 to 8, are characterized with deep bedrock overlayed by thick unconsolidated Quaternary deposits. These materials show low average shear wave velocity in the upper 30 meters below the surface (Vs30), and their thickness enables amplification of seismic waves and the emergence of local site effects.