Ground-Motion Model Considering the Effects of Wave Propagation Direction and Topography in Pohang, South Korea

We develop a model to predict the amplification of ground motion for 5% damped pseudospectral accelerations for periods ranging from 0.01 to 0.5 s while considering the effects of varying topography. We use 487 ground motions recorded at densely deployed 118 temporary stations and one regular seismic station in Pohang, South Korea. The proposed model depends on the magnitude of detected motions and the distance from the epicenter. In addition to the relative elevation, we newly introduce the azimuth angle from the station to the epicenter relative to slope aspect as an important topography parameter, which we denote as α. We observe that ground motions are deamplified when the relative elevation is lower than −18 m, and the angle α is smaller than 90° (the slope faces the epicenter). When relative elevation is higher than 14 m, ground motions are amplified for α<90° and deamplified for α>90° (the slope is facing away from the epicenter). The ground motions are not affected by the angle α when the relative elevation ranges from −18 to 14 m. Finally, we propose a predictive model as a function of earthquake magnitude, epicentral distance, relative elevation, and α.