In a project on earthquake strong ground motion selection and scaling for the analysis of transportation structural and geotechnical systems at locations throughout California (or regions where seismic hazard is dominated by mid-to-large-magnitude crustal earthquakes at near-to-moderate distances) PEER-funded researchers, Jack Baker et al, developed a new selection algorithm that allows the user to select a set of ground motions whose response spectra match a target mean and variance. The research is outlined in PEER Report 2011/03 – New Ground Motion Selection Procedures and Selected Motions for the PEER Transportation Research Program by Jack W. Baker, Ting Lin, Shrey K. Shahi, and Nirmal Jayaram. The algorithm is based on the empirically verified observation that the set of logarithmic spectral accelerations at various periods is a random vector that follows a multivariate normal distribution (Jayaram and Baker 2008). This algorithm was used to generate five sample sets of standardized earthquake strong ground motion records from the PEER Next Generation Attenuation (NGA) Project ground motion library of 3,551 multi-component ground motions from 173 earthquakes ranging in magnitudes from 4.3 to 7.9, primarily from shallow crustal earthquakes in seismically active regions of the world. The following five suites of ground motions representing different magnitudes, soil conditions, distances from rupture, etc. are available for download from the PEER Ground Motion for Transportation pages:
Set #1a: Broad-band ground motions (M = 7, R = 10 km, soil site)
Set #1b: Broad-band ground motions (M = 6, R = 25 km, soil site)
Set #2: Broad-band ground motions (M = 7, R = 10 km, rock site)
Set #3: Pulse-like ground motions
Set #4: Site-specific ground motions for Oakland consists of ground motions selected to match the uniform hazard spectrum and associated causal events for a site in Oakland, California. Forty ground motions are provided to represent the ground motion hazard at each of three hazard levels (2%, 10% and 50% probabilities of exceedance in 50 years).
For situations where recorded strong ground motions for specified earthquake and site characteristics are limited in number, synthetic ground motions that can supplement or supplant recorded motions for analysis for a wide spectrum of earthquake and site characteristics can be developed stochastically. In another PEER-funded, transportation systems study, by identifying the parameters of the stochastic model for a large sample of recorded accelerograms drawn from the NGA library, predictive equations are developed that empirically relate the model parameters to a set of earthquake and site characteristics. Using these equations, for specified earthquake and site characteristics, sets of the model parameters are generated that are used in the stochastic model to generate an ensemble of synthetic ground motions. The resulting synthetic accelerations, as well as corresponding velocity and displacement time-histories, capture the main features of real earthquake ground motions, including the evolving intensity, duration, spectral content, natural variability, and peak values. Furthermore, the statistics of their resulting elastic response spectra, i.e., the median and logarithmic standard deviation, closely agree with values predicted by the NGA ground motion prediction equations. The research is documented in PEER 2010/02 – Stochastic Modeling and Simulation of Ground Motions for Performance-Based Earthquake Engineering by Sanaz Rezaeian and Armen Der Kiureghian.