SEISMIC HAZARD DISAGGREGA-\TION OF ETA IN CONDITIONAL SPECTRA

Selection of appropriate ground motion is a key element within any seismic assessment of structures. Many methodologies have been developed in order to select and scale ground motion records for the purpose of response history analysis. UHS is one of those developments and has been widely used in performance based earthquake engineering. However, implementation of UHS is somewhat conservative when used as a proxy for ground motion selection processes, since it is very unlikely to nd a record which has a spectrum as high as the UHS. Spectral shape indicators, including Epsilon and Eta, have been recently proposed in order to take a wide range of spectra into account. Additionally, conditional mean spectra have been obtained by the mentioned indicators which can be used as the target design spectra, e.g; Conditional Mean Spectrum (CMS) and Eta-based Conditional Mean Spectrum (ECMS). The Eta indicator uses the conventional epsilon in combination with the peak ground velocity epsilon. As the peak ground velocity epsilon is not convenient in seismic hazard disaggregation, a simple formula was proposed by Mousavi et al. to approximate the target peak ground velocity epsilon based on the conventional epsilon. However, this simple formula needs to be investigated more precisely. Therefore, a comprehensive seismic hazard disaggregation is proposed, in this paper, to explicitly obtain the target peak ground velocity epsilon. An ideal site, with a single linear fault, was assumed in order to obtain the target peak ground velocity epsilon. The results show that the exact target peak ground velocity epsilon is meaningfully dierent from the simple formula in this issue, and the resulted conditional spectra are sensitive to this renement in the low period range when using the exact target peak ground velocity epsilon.