QUALITATIVE EVALUATION OF F-VALUES OF LONG-PERIOD GROUND MOTIONS FOR DESIGN EARTHQUAKE MOTIONS

The goal in this study is to propose a method that evaluates a design earthquake ground motion by using a velocity spectrum (SV-spectrum) which represents the maximum response of a structure, an energy spectrum (VE-spectrum) which reflects the input energy into a structure, and an f-value (Akiyama,Kitamura,2006) as the ratio of an average SV-spectrum and an average VE-spectrum. The proposed method has the advantage of being able to adjust the input energy at each site easily by the VE-spectrum without changing the maximum response. In this paper, as the first-step in this study, we evaluated the characteristics of an f-value. First, we analyzed the values of an average SV-spectrum, an average VE-spectrum, and an f-value for every divided range of periods (0.1-1s, 1-2s, 2-3s, 3-10s) by using the observed ground motion records of the 2011 off the Pacific coast of Tohoku Earthquake and the 2003 Tokachi-Oki Earthquake. Next, we evaluated the relationship between the f-value and the fault distance, the magnitude of the earthquake, or the site characteristics. Finally, we have shown that the f-value tends to depend on the fault distance and the magnitude of the earthquake in the short-period range, and to vary with the site characteristics in the long-period range.