SIGMA: a new tool for the simulation of spectrum-compatible earthquake ground motions

In earthquake engineering, the selection of input ground motion is crucial for applications in nonlinear dynamic analyses of structures and geotechnical systems. Ground motion simulation can be a valid alternative to natural ground motions, which can be scarce for certain combinations of earthquake scenarios and site conditions, especially for large, infrequent earthquakes. In addition, they can avoid using disproportionate scale factors to achieve spectrum compatibility, which may affect the consistency of the scaled records with the original seismological parameters. This work presents a methodology allowing generating a specific number of spectrum-compatible simulated ground motions given a few input parameters: magnitude, distance, VS30, depth and faulting style. A software tool implementing the simulation of ground motion records is also provided. The time series are simulated with an up-to-date non-stationary stochastic model calibrated using a ground motion predictive equation derived from the Italian strong motion database. The spectrum-compatible accelerograms are selected among hundreds of simulations using an innovative optimization technique based on a genetic algorithm, which finds the combination of records with the smallest deviation with respect to the target response spectrum (e.g. seismic code spectrum). An example of the procedure applied to specific earthquake scenarios is provided, including the probabilistic seismic hazard assessment for two case studies and a comparison with the natural ground motion records selection. This procedure allows for the simulation of a desired number of realistic ground motions, representing a valid alternative to natural ground motions to be used in nonlinear analyses in the time domain of civil structures.