Validation of Two Approaches for Expressing Spectral Decay Characteristics of Ground Motions in High Frequency Range - Fmax and Kappa Models -

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Spectral decay characteristics in high frequency range of observed ground motions during inland crustal earthquakes have been evaluated using two different approaches: f_max (Hanks, 1982) and kappa (Anderson and Hough, 1984) models. We analyzed 105 events (M_w 3.3-7.0) including seven large earthquakes (M_w 5.9-7.0). For large earthquakes, we estimated cut-off frequency f_max to range from 6.5 to 9.9 Hz and the power coefficient of spectral decay s from 0.78 to 1.60 in the f_max model, and kappa to range from 0.0142 to 0.0505 and f_E from 2 to 4.5 Hz in the kappa model in our previous study (Tsurugi et al., 2017). The f_E in the kappa model is a specific frequency at which a spectrum starts to decrease linearly with increasing frequency in log-linear space.

In this paper, we examined the validity of the two models in expressing high-frequency spectral decay characteristics by calculating the residual error between the observed Fourier amplitude spectra and two theoretical spectra, one from the omega-squared source model (Aki, 1967; Brune, 1970) and the f_max model, and the other from the kappa model. We calculated residual errors for each frequency and for each earthquake. As a result, we can say that both approaches using the f_max model and the kappa model are appropriate to evaluate spectral decay characteristics in high frequency range, if the parameters for the spectral decay characteristics (i.e., f_max and the power coefficient of spectral decay s in f_max model, or the parameter kappa and the specific frequency f_E in kappa model) are appropriately evaluated by observed spectra.

This study is a part of the regulatory-supported research project funded by the Secretariat of Nuclear Regulation Authority, Japan.

Reference

Aki (1967), JGR 72, 1217-1231.

Anderson and Hough (1984), BSSA 74, 1969-1993.

Brune (1970), JGR 75, 4997-5009.

Hanks (1982), BSSA 72, 1867-1879.

Tsurugi, Kagawa, and Irikura (2017), 16WCEE, No.1232.

Presenting Author: Masato Tsurugi

Authors