From regional- to local-scale seismic hazard assessment: examples from Southern Spain

An approach that relates results from a regional seismic hazard assessment study with local-scale site-effect characterizations in an area of low-to-moderate seismic activity such as Andalusia (southern Spain), is presented. Results of a previous probabilistic seismic hazard analysis of Andalusia on rock conditions are disaggregated to infer hazard controlling earthquakes for different target motions. A collection of controlling magnitude-distance pairs and the corresponding site-specific response spectra at main capital cities of the region are obtained. These spectra are first-order approximations to expected seismic actions required in local earthquake risk assessments. In addition, results of independent, local-scale studies developed in Almeria City (SE Andalusia) are used to derive an updated seismic zonation of the city. These include predominant soil period estimates and shear-wave velocity profiles at different locations. If a local seismic risk assessment study or an earthquake-resistant structural design is to be developed, it may be recommended the use of different seismic actions on sites characterized by distinct response to seismic shaking (as derived from the seismic zonation). The seismic action related to worst-case scenarios may be modeled through a hazard-consistent response spectrum, obtained by hazard disaggregation at the spectral acceleration with period matching the prevailing resonant period of the target site or structure.