A Semi-Empirical Analysis of Strong-Motion Peaks in Terms of Seismic Source, Propagation Path and Local Site Conditions
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The purpose of this report is to derive a new type of semi-empirical expression for scaling strong-motion peaks in terms of seismic source, propagation path and local site conditions. Peak acceleration, peak velocity and peak displacement are analyzed in a similar fashion because they are interrelated. However, emphasis is placed on the peak velocity which is a key ground motion parameter for lifeline earthquake engineering studies. With the help of seismic source theories, the semi-empirical model is derived using strong motions obtained in Japan. In the derivation, statistical considerations are used in the selection of the model itself and the model parameters. Earthquake magnitude M and hypocentral distance r are selected as independent variables and the dummy variables are introduced to identify the amplification factor due to individual local site conditions. The resulting semi-empirical expressions for the peak acceleration velocity and displacement are then compared with strong-motion data observed during three earthquakes in the U.S. and Mexico. This comparison suggests that the proposed semi-empirical model is superior to existing models for strong ground motion peaks. The amplification factors for acceleration, velocity and displacement peaks obtained empirically by the model are found to be period-dependent and related to local soil conditions. In addition, two methods for predicting the amplification factor at a new site are proposed. Finally, a simplified method for estimating maximum soil strain is presented with the aid of the proposed semi-empirical expression for the peak velocity.