Direction-Dependent Analysis of Parameters for Stochastic Synthesis of Vertical Ground Motion

Abstract eng:
For synthesis of tridimensional ground motions, the available deterministic approach is no longer efficient in high frequency range (say, >1 Hz) for computational limitation and limited knowledge on small-scale heterogeneity in the regional crust, while the widely adopted stochastic synthesis, up to now only working for undirectional horizontal record, needs to be developed further for vertical component. A research on the direction-dependence of key seismic parameters in the stochastic method, such as stress parameter, quality factor, radiation pattern, kappa factor and site amplification, is presented in this paper to evaluate the different effects of crustal inhomogeneity on vertical and horizontal components. The result indicates that the first two are just region-specific parameters of the crust medium property and status, whereas the other three are complicatedly and strongly direction-dependent. Then, we incorporate the direction-dependent pattern based on Pulido’s research for an accurate energy distribution of wave radiated from the source, and take the difference between vertical and horizontal kappa factor and site amplification into account. Vertical ground motions for the 1994 Northridge earthquake are synthesized with these improvements, and the comparisons with the observed motions show reasonable agreement in average, which is followed by further validation to demonstrate the accordance with the recently developed vertical ground motion predication equations.

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