Probabilistic Seismic Hazard Analysis for Maximum Seismic Shear Stresses in Soils Using Improved Ground-Motion Parameters

Maximum seismic shear stresses (tau(max)) have been recognized as one of the important parameters in design practice. This study develops ground-motion parameters for tau(max) and implements these in probabilistic seismic hazard analysis to provide the tau(max) distribution of deep soil layers for design purposes. The application of improved ground-motion parameters for tau(max) is demonstrated at the Oakland International Airport, where a thick Young Bay Mud deposit exists under the artificial fill. Model biases in the predictive equations of seismic shear-stress reduction coefficients (r(d)) are evaluated by comparison with the site response analyses performed with a wide range of input ground motions. Based on these results, we introduce improved ground-motion parameters for tau(max) (I-tau) as a linear combination of spectral accelerations, implemented in probabilistic seismic hazard analysis to calculate seismic hazard curves. Conditional mean spectra are calculated, given I-tau at 10% in 50 years to illustrate the variations in frequency contents with depth compared with the uniform hazard spectra. Finally, tau(max) is calculated with depth by using hazard values of I-tau and compared with the peak-ground-acceleration-based and uniform-hazard-spectra-based calculations. Analysis results show that tau(max) will be underestimated for deep soil layers by peak-ground-acceleration-based calculation if the median value of r(d) is used in design practice. DOI: 10.1061/(ASCE)GT.1943-5606.0000740. (C) 2013 American Society of Civil Engineers.