Characteristics of Rock Motions During Earthquakes

Rock motions during earthquakes are characterized in terms of the maximum amplitude of accelerations, the predominant period of the motions, and the duration of the motions. It is shown that these characteristics depend mainly on the magnitude of the earthquake and distance of the site from the zone of energy release. Available data relating the rock motion characteristics to the magnitude of the earthquake and the distance to the causative fault are presented and used to establish a general procedure for assessing the maximum acceleration, the predominant period, the duration of shaking and the time history of accelerations developed during any given earthquake. As an example, the rock motions at the E1 Centro site (for the 1940 E1 Centro earthquake) are estimated using the proposed procedure and incorporated in analyses of the response of the site. The computed surface motions are shown to be in good agreement with those recorded during the 1940 E1 Centro earthquake.