Coherency Function Model of Seismic Ground Motion Based on Accelerograms Recorded by Zigong Seismograph Array

Zigong Seismograph Array (ZGSA), located in Sichuan province of China, was installed in 2007 and included 8 irregularly-spaced seismograph stations. The array successfully recorded strong motions during the 2008 Wenchuan earthquake (Ms 8.0). Because the separation distances between every two stations are less than 400 meters, these data offer some interesting insights into spatial variations of seismic ground motions that suits for engineering scale. In this study, authors firstly calculated the coherency functions of accelerations at different directions recorded by ZGSA through application of digital signal processing technology. Then, the variation mechanisms of the coherency functions at various directions, along with the separation distance and frequency changes, were analyzed. The results showed that when the circular frequency was less than 3Π, the coherency function was more than 0.8. However, the degressive trend of the coherency function became significant with the separation distance elongation when frequency gradually increased. Consequently, based on the recordings, a piecewise fitting model was put forward to simulate the spatial variation of seismic ground motion under the conditions of large-earthquake and far-field. The spatial coherency model proposed in this paper has applicable value in simulation study of ground motion field.