Abstract
In Japan the way of determining seismic intensity by JMA (Japan Meteorological Agency) changed from perceptual to instrumental in 1996, immediately after the Kobe earthquake. This new instrumental seismic intensity is known as a useful measure to estimate the earthquake ground motion. We here examine the relations between seismic intensities and various quantities of earthquake observation records such as peak acceleration, peak velocity, spectral intensity, etc., focusing especially on the seismic intensity range equal to or higher than 4 on the JMA scale. The response spectral characteristics of two records with the same seismic intensity are compared. The peak values of the spectrum and predominant periods are found different and this evidence facilitates the necessity of introducing a combined seismic intensity, that is, of modifying from a single-valued one to a three-valued seismic intensity, especially at making clear the difference of damage to structures with shorter and longer natural periods.
