The Coherency Between Ground Motions Synthesized For Input Into The Analysis Of A Large Span Structure

In order to meet the requirement of non-consistent input for seismic analysis of a large span structure with multiple supports, the coherency of a synthesized ground motion field is validated in this paper. The result shows that the correlation between motions close to each other on a rock site is strong, the mean values of coherencies range from 0.7 to 0.8 and the maximum is up to 1.0. The coherency decreases with the distance between the motion points. The correlation between low frequency motions close to each other on a soft soil site is very strong, the mean of coherencies is larger than 0.8. The correlation of low frequency motions decreases also with the distance. The correlation between high frequency motions (> 5 Hz) is weak, the coherencies corresponding to various distances are all less than 0.5 and the mean is mostly less than 0.25. The result is consistent with the conclusion from the statistics of the observed data on some dense arrays like SMART-1 during the past earthquakes.