The Duration and Amplitude Characteristics of Earthquake Ground Motions with Emphasis on Local Site Effects

Among various indices of earthquake ground motions, the maximum amplitude value and frequency content have been regarded as the most important indices for earthquake engineering. These indices are strongly affected by local site conditions. Also the fact that the duration of earthquake ground motion differs from site to site even during the same earthquake has been noticed by many researchers. This paper dealt with the duration and its related parameters were adopted as representative parameter of the duration characteristics of earthquake ground motions. We investigated how they are influenced by the earthquake magnitude, hypocentral distance and the focal depth. The average and overall trends of the duration and its related parameters were presented. Also the correlation of the duration and its related parameters with the Japan Meteorological Agency (JMA) instrumental seismic intensity was shown. A simple statistical technique was performed by using the earthquake ground motion records obtained in the Sendai region, Japan. This paper discusses the variability for the duration and its related parameters with emphasis on the site-dependency and the event-dependency to reveal the duration and amplitude characteristics of earthquake ground motions. The difference of these ground motion parameters is not only site-dependent but also event-dependent. For the total power and rms amplitude, the difference at each site exceeds the variability at each event, and strong site-dependency was found. The variability for the total power, rms amplitude and peak ground acceleration (PGA) indicated essentially the same trends. On the other hand, it is quantitatively revealed that the event-dependency for the duration is greater than the site-dependency. Among various ground motion parameters, these parameters would be divided into two groups regarding the site-dependency and the event-dependency. One is the ground motion parameter based on “amplitude”, and the other based on “duration”. In addition, this paper suggested that the duration and amplitude characteristics of earthquake ground motions suffer a reciprocal effect due to the earthquake magnitude, hypocentral distance, the focal depth and the local site conditions. In view of the results, the duration is not less important than the maximum amplitude and frequency content in earthquake engineering. Furthermore, this paper provided meaningful information of input motion available to earthquake-resistant design.