Selecting and Scaling Strong Ground Motion Records Based on Conditional Mean Spectra. Case Study for Iasi City in Romania

Abstract

The Conditional Mean Spectrum (CMS) represents one of the versatile tools for selecting and scaling the strong ground motion records for a particular site. The procedure to obtain the Conditional Mean Spectrum (CMS) presented in Baker (2011) is applied for Iasi City in N-E Romania, the second largest Romanian city in terms of seismic risk. The major seismic hazard for most of Romanian territory is dominated by the Vrancea intermediate-depth seismic source. The ground motion prediction model, proposed in Vacareanu et al. (2015) for intermediate-depth earthquakes, is used for the computation of Uniform Hazard Spectrum (UHS) and the Conditional Mean Spectrum (CMS) at a vibration period of T = 1.0 s in Iasi City. The spectral period of 1.0 s is considered to be representative for the new stock of residential and office RC buildings in Romania. Disaggregation of seismic hazard is performed in order to determine mean causal values of magnitude, source-to-site-distance and epsilon. Empirical correlations between epsilon values at different vibration periods are calculated using a set of strong ground motions recorded during ten intermediate-depth Vrancea earthquakes. Moreover, based on the empirical values of the correlation coefficients, corresponding predictive relations are developed specifically for strong ground motions generated by Vrancea intermediate-depth earthquakes. Record selection and scaling based on the criteria proposed by Baker and Cornell (2006) and Baker (2011) is performed for Iasi City using a database consisting of strong ground motions recorded during Vrancea intermediate-depth earthquakes with moment magnitude larger than 6.0.