Seismic Microzonation Of The Medellin Area Using A Probabilistic Approach

A seismic microzonation evaluation allows identifying the soil amplification effects at any location within an area of study. The results of this evaluation are expressed as soil amplification factors which are usually integrated into standard probabilistic hazard assessment models or into pre-defined building design methodologies. In this study, we use the Medellin case (the second largest city in Colombia) to implement a rigorous methodology to obtain soil spectral amplification factors that represent the dynamic response of any given zone in which it is expected a similar seismic response. These spectral amplification factors are applied to uniform hazard spectra at bedrock to obtain amplified spectra at ground level. In order to consider the main sources of uncertainty, statistical variations of the parameters that characterize the soil profile are evaluated using the available representative geotechnical information within each zone. Monte Carlo simulation techniques are used to generate a set of representative onedimensional simulation models considering all possible variations in the soil profile and assigned parameters. Each representative model is used to obtain the corresponding spectral amplification factors for the set of seismic records selected for the dynamic analysis. Spectral amplification factors are calculated for the range of expected soil vibration periods that are measured inside each zone. Simultaneously, a soil vibration period map is generated using all possible sources of information, mainly field measurements. The soil vibration period map is used to geographically assign the corresponding spectral amplification factor. In this study, the results are presented as a set of spectral amplification factors for various seismic intensities and ranges of the soil vibration period within each soil profile characterization.