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| Coherence analysis for ground motions with variation of site depth |
| HONG Na1,2,CHEN Qingjun1,2 |
1.State Key Lab of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;
2.Research Institute of Structural Engineering and Disaster Prevention, Tongji University, Shanghai 200092, China |
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Abstract At present, the research on the coherency of seismic ground motions is almost limited to the coherency problem of ground motion in free field. In order to investigate the variability of seismic ground motions on depth and seek a model to simulate coherency of ground motions function varied with depth for different types of sites, 2679 pairs of ground motion records were collected from KiK-net of Japan in this paper. The random vibration theory and the digital signal processing techniques were used to study the coherency varied with depth. By fitting the calculated coherency function of horizontal components of ground motions, a coherency model with unified mathematical expression for different sites was proposed and the corresponding parameters were analyzed. The results show that there is no significant dependence between the estimated coherencies from different earthquake magnitudes or epicentral distance (less than 200 km); shear wave velocity(VS) plays an significant role on depth coherency and compared with Vs of shallow soil, the effect of Vs of deep soil on depth coherency is notable; the coherence function varied with depth for horizontal components has an exponential reduction tendency along with increasing depth and frequency, and frequency plays a more significant effect on the velocity of coherency function than depth. Coherency function is site dependent: the softer the site condition, the faster decay the coherencies with depth.
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Received: 11 May 2018
Published: 28 April 2019
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