New Frequency Domain–Based Inverse Ground Response Analysis Framework for the Determination of Dynamic Soil Properties

Abstract

Dynamic soil properties curves (DSPCs) [that consist of modulus reduction (G/Gmax) and damping ratio (β) curves] are important input parameters for ground response analysis (GRA). However, due to the nonavailability of regional DSPCs, in most cases, regional GRA is carried out based on globally established DSPCs. It is noted that the issue of spatial variability in the previously established DSPCs has been raised in numerous studies. In addition, for most of the cases where GRA is based on previously established DSPC’s from other regions, whether their outcome for surface seismic hazard applies to the region under consideration is debatable. Although the determination of regional DSPCs based on laboratory tests can be carried out, this method is flawed due to sample disturbances and equipment compliance. Under these circumstances, inverse GRA performed on downhole seismic array records can be used to determine in situ DSPCs. However, existing inverse GRA frameworks have limitations, one of them being the estimation of DSPCs for combined layers that only exist between successive accelerometers and not for individual soil layers or type. In addition, although frameworks do exist to determine G/Gmax for a combined layer, to date there is no consistent approach that can be carried out to estimate β from inverse GRA in the frequency domain. This study proposes a new framework to estimate G/Gmax, β, and shear strain (γ) that follows frequency domain methodology. The proposed framework will be applied to records from a downhole array located in Lotung in the central part of Yilan County, Taiwan and IWTH27 from the Kiban Kyoshin network (KiK-net) array in Japan following which G/Gmax, β, and γ for the surficial layer will be determined. It is noted that the proposed methodology could be used to determine the DSPCs for recorded ground motions that exist at the top and bottom of a layer as well as for a surface layer that is underlain by rock with ground motions available at the surface and within the rock medium.