Spectral Decay Characteristics Fmax and κ for Strong Ground Motion Prediction

Abstract eng:
Spectral decay characteristics of ground motions for inland crustal earthquakes in Japan are examined. It is very important to clear spectral decay characteristics in high frequency range for strong ground motion prediction. Total number of analyzed target earthquakes is 65 and those moment magnitudes (M w ) are from 3.6 to 6.9. Four large earthquakes (M w >5.9) are included in the target earthquakes. In this study, spectral decay characteristics in high frequency range are evaluated by two approaches. One is f max filter, the other is spectral decay parameter, κ (Kappa). In result, f max ’s of four large earthquakes are estimated to be 6.5Hz to 9.4Hz and f max filter shapes of four large earthquakes are almost same. Larger the earthquakes are, smaller f max ’s tend to be. Correction filter, P C (f), which is a filter to correct difference of spectral decay characteristics between large and small earthquakes are suggested. κ’s of four large earthquakes are estimated to be 0.0142 to 0.0277. There are positive correlation between s as power coefficient of high-frequency decay of f max filter and κ as spectral decay parameter and between f max for the f max filter and f E for parameter κ. f E is a frequency at which spectrum starts to decrease on log-linear scale. f E is a very important parameter for strong ground motion prediction, however f E has not been examined carefully enough in previous studies. It is confirmed that corrected high frequency characteristics using f max filter are almost same as that using spectral decay parameter, κ agree well each other. Both methods, f max filter and spectral decay parameter, κ, provided us almost the same high frequency spectral characteristics to predict strong ground motions, as long as the parameters, f max and s for the f max filter and κ and f E for the spectral decay parameter are empiricaly given.

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