Geozonation of the Zagreb city area as an input for seismic risk assessment

The Zagreb city area is located in a geologically diverse and complex area: on the southern slopes of Medvednica Mountain, the alluvial plains of the Sava River, and on the northern slopes of the Vukomeričke gorice hilly area. The urbanisation of this relatively large area is an ongoing process, and nowadays, the city’s development is proceeding rapidly in unfavourable locations in terms of geohazards, meaning that areas with a possible seismic, flood, or landslide risk are becoming increasingly populated. To achieve sustainable development, geohazards and ground types need to be addressed and assessed for the whole area of Zagreb city as the input for seismic risk assessment. As one step in that direction, existing geological data were reviewed and analysed, and accordingly, geozonation of the Zagreb city area was carried out, differentiating four zones with six geological complexes. Based on the available geological data, we assessed the geohazard processes, ground types, and seismic risk for each differentiated zone and complex, and in that way, a smallscale regional zonation map was developed. Further detailed geo-research of the Zagreb city area is recommended as the city area is relatively large and heterogeneous in terms of geological settings, and detailed geo-data are needed to define local geo-conditions, geohazards, and ground types. With detailed geo-data, the presented geozonation of the Zagreb city area could be upscaled and directly applied in urban planning. The presented results were used as input for the seismic risk assessment for the research area, and the developed regional map is already being used by the local government.