HIGH-CUT FILTER DUE TO MAINSHOCK AND AFTERSHOCKS OF THE 2005 FUKUOKA-KEN SEIHO OKI EARTHQUAKE USING KiK-net DATA

Abstract

Spectral decay characteristics in high frequency range due to mainshock and aftershocks of the 2005 Fukuoka-ken Seiho Oki Earthquake are examined. The Butterworth type high-cut filter with cut-off frequency f_max and its power coefficient is assumed in this study. The two parameters are estimated by fitting Fourier spectra of observed records at rock sites with the theoretical filter shape. In result, the cut-off frequency f_max of the mainshock is estimated as 6.5Hz. This value is almost same as that of the 1995 Hyogo-ken Nambu Earthquake. The cut off frequencies f_max of aftershocks are estimated in the range about 9Hz and 20Hz.