# Study on the Influence of a Soft Soil Interlayer on Spatially Varying Ground Motions
## 5 Conclusions  
By using two numerical examples and based on previously established time-varying transfer function model incorporating the influence of soil non-linearity, the influence regularity of the properties of soft soil interlayer on the lagged spatial coherency between spatially varying earthquake ground motions was studied in the present paper, where the variation trend of lagged coherency loss with the shear wave velocity, thickness, and burial depth of soft soil interlayer was mainly focused on and relevant analyses were presented. The difference of spatial coherency characteristics between linear elastic soil and non-linear soil cases was generally evaluated, and the reason why the difference showed up is given. Some important conclusions are drawn:  
1. As the shear wave velocity of interlayer declines and as the buried depth and thickness increase, remarkable reduction of spatial coherency shows up;
2. The reduction of lagged spatial coherency caused by varying buried depth may be more inclined to concentrate in the lower frequency range;
3. The non-linear soil behavior can cause greater further reduction of lagged spatial coherency in comparison with linear soil behavior, especially in the higher frequency range;
4. The troughs of lagged spatial coherency curve tend to be located in the variation range of vibration frequency of time-varying spectral ratio.  
Due to the further reduction of spatial coherency resulted from the existence of soft interlayer and non-linear soil behavior, the cross correlation between spatially varying earthquake ground motions on sites j and k may be lower and thus greater randomness of simulated ground motions might appear. Therefore, the local seismic responses of large-scale structures might present larger differences, which may cause more severe damage to structures. The results of the present paper shed light on the influence regularity of local soft soil interlayer on the spatial coherency between spatially varying earthquake ground motions so as to facilitate the simulation of seismic motions on a site containing local soft soil interlayer and to thoroughly study the effect of local soft soil interlayer on the seismic response of extended structures. Besides, to some extent, this research provides reference for further study in this field.  
Conceptualization, E.Y.; Data curation, L.Y.; methodology, E.Y.; software, E.Y.; validation, W.L.; writing--original draft preparation, E.Y.; writing--review and editing, Z.Y.; visualization, W.L.; supervision, Y.M.; project administration, Z.Y.; funding acquisition, E.Y., Z.Y. and Y.M. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Grant numbers: 51908236, 52109148, 51978304, and 51778260), the China Postdoctoral Science foundation (Grant number: 2019M652649), the Foundation of Hubei Key Laboratory of Blasting Engineering (Grantnumber: BL2021-14), and the Scientific Research Operating Expenses of the Central Government (Grant number: CKSF2021461/YT).  
This study was financially supported by the National Natural Science Foundation of China (Nos. 51908236, 52109148, 51978304, and 51778260), the China Postdoctoral Science foundation (2019M652649), the Foundation of Hubei Key Laboratory of Blasting Engineering (No. BL2021-14), and the Scientific Research Operating Expenses of the Central Government (No. CKSF2021461/YT). The first author also wants to thank his girlfriend, [PERSON], for her care.  
The authors declare that they have no conflict of interest.