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SeisRICHerCRO: Mapping the local site effects from the analysis of ambient noise measurements in earthquake-prone (with significant cultural heritage buildings) areas in Croatia

The most seismically active regions in Croatia are the coastal region and the north-western part of Croatia, regions that have numerous cultural heritage sites. Therefore, it is important to estimate seismic risk for cultural heritage sites and to develop procedures for seismic risk assessment. These are the goals of the research project Seismic Risk Assessment of Cultural Heritage Buildings in Croatia (SeisRICHerCRO) funded by the Croatian Science Foundation. The targeted locations of the project are Trakošćan Castle, the Cathedral of St. Jacob in Šibenik and the old city centre of Dubrovnik. The project has many objectives: investigation of seismicity according to the compiled earthquake catalogue, determination of local site characteristics, numerical analysis of local seismic site response, determination of dynamic characteristics of selected buildings, seismic hazard assessment, seismic vulnerability and risk assessment and finally coordination and administration. Microtremor measurements were carried out at all three targeted locations: Trakošćan Castle (approx. 0.1 km2, 36 measurements), in the proximity of the Cathedral of St. Jacob in Šibenik (approx. 0.15 km2, 108 measurements) and in the old city centre of Dubrovnik (approx. 0.2 km2, 115 measurements). Based on individual microtremor measurements, maps of fundamental site frequencies were derived. Following the empirical relationship between resonance site frequency, bedrock depth and Vs30 for Croatia, maps of average shear wave velocity in the upper 30 m (Vs30) and bedrock depth (H800- depth of the bedrock formation identified by shear wave velocity VS ≥ 800 m/s) were also derived. Presented maps can help to distinguish potentially dangerous seismic zones in the all three targeted locations: a) soil-structure (building) resonance at fundamental site frequencies, b) Vs30 is important for Eurocode 8 classification, and c) bedrock depths are important for numerical site response analysis for the estimation of site amplification. Comprehensive seismic microzonation maps incorporating seismic site amplification data provide input data for earthquake-resistant designs as well as the construction and reconstruction of important buildings and are also useful for urban planning that utilises spatial master plans.

local site effects, Croatia, SeisRICHerCRO, cultural heritage

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