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Synthetic earthquake ground motions at closely spaced distances with SYNACC

An abstract of the technical paper presented at:
San Francisco, California, USA
August 18–23, 2013

Prepared by:
Maria I Todorovska1, Mihailo D. Trifunac, Vincent W. Lee2 and Nebojsa Orbovic3

1Research Professor, Dept. of Civil Engineering, U. Southern California, Los Angeles, CA
2Professor, Dept. of Civil Engineering, U. Southern California, Los Angeles, CA
3Technical Specialist, CNSC, Ottawa, ON, Canada


This paper presents a brief review of the SYNACC method for synthesizing earthquake ground motion time histories on an array of points in space. SYNACC is a combination of an empirical and physical model-based method and involves unfolding in time a site-specific Fourier amplitude spectrum of ground acceleration obtained for a scenario earthquake by an empirical scaling model. The unfolding consists of representing the ground motion as a superposition of traveling surface Love and Rayleigh waves and of body P and S waves, which propagate with phase and group velocities consistent with the dispersion characteristic of the site geology, approximated by parallel layers. Because the coefficients of expansion are scaled so that the Fourier spectrum of the synthetic motion matches a site-specific empirical spectrum, the synthetic motions are consistent statistically with observations within the recording range of typical accelorographs (0.02–25 Hz). A uniform hazard Fourier spectrum or any specified Fourier spectrum can also be used as a target spectrum. The output consists of synthetic accelerations, velocities and displacements, and point strains, rotations and curvatures, all at a point or at an array of points. Such time histories are useful for the design of spatially extended structures, like pipelines, tunnels and nuclear islands.

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