Study on a High-Cut Filter for Strong Ground Motion Prediction (Part3)

- Based on The Observed Records During Crustal Earthquakes in Japan -

Abstract

Spectral decay characteristics in high frequency range due to large and small inland crustal earthquakes that occurred in Japan are examined. The Butterworth type high-cut filter with cut-off frequency, f_max and its power coefficient of high-frequency decay is assumed in this study. Four parameters such as seismic moment M_o, corner frequency f_c, f_max, and its power coefficient s are estimated by comparing observed spectra at hard rock sites with theoretical spectra. The theoretical spectra are calculated, based on the omega squared source characteristics convolved with propagation-path effects and f_max filter shapes. In result, f_max's of six large earthquakes are estimated to be 7Hz to 10Hz and those of small earthquakes are estimated to be 9Hz to 20Hz. The power coefficients of the f_max filter, s, for earthquakes in Shizuoka and Kumamoto regions are larger than those for earthquakes in other regions. Therefore, a region dependency of spectral decay characteristic is suggested. Moreover, correction filter, P_C(f), a filter to correct the difference of spectral decay characteristics between large and small earthquakes, are suggested. Finally, effects of spectral decay characteristics from large earthquakes on strong ground motion prediction are examined. The results in this study contribute to strong ground motion prediction in high frequency range.