On the Use of the High-Frequency Spectral Decay Parameter (κ0) to Constrain Large Strain Site Response Analysis

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications
Type: Oral
Date: 4/28/2020
Time: 04:45 PM
Room: 110 + 140
Description: 

The high-frequency spectral decay parameter (k_0­) is a seismological parameter that is used to model the exponential decay of the Fourier Amplitude Spectrum (FAS) of acceleration at high frequencies and it can be related to the attenuation (Q) and shear wave velocity (Vs) profiles at a site. Due to this relationship and the fact that k_0­ can be estimated from surface ground motion recordings, the parameter k₀ can play an important role in constraining site response analyses. This presentation will summarize recent efforts that use k_0­ to modify the results from equivalent-linear (EQL) site response analysis at large strains.

It is well-known that EQL analysis can overdamp high frequencies when large strains are induced in the soil, leading to unrealistic response spectra at high frequencies. The parameter k_0­ potentially can be used to modify the surface motion predicted by EQL analysis, if an appropriate large-strain target k_0­ can be determined. Recent research using small-strain and large-strain motions recorded at the same sites shows that k_0­ does not systematically increase with increasing shear strain, indicating that the small-strain k_0­ can be used as the target k₀ for large-strain motions. This approach of using the small-strain k₀ to modify the surface motion predicted by EQL analysis for high intensity/large strain motions is tested using several Kik-Net downhole array sites in Japan. Across a large range of frequencies and induced shear strain levels, the k₀ modification approach results in unbiased estimates of site amplification.

Presenting Author: Ellen Rathje

Authors