Non-isotropic and Isotropic Ground Motion Prediction Models

Ground motion models have a significant role in probabilistic seismic hazard analysis. In 2013, new event-specific isotropic and non-isotropic ground motion models were introduced by Raschke (J Seismol 17(4):1157-1182, 2013), where non-isotropic behavior is applied by unit isolines. In this study, explicit equations of two different unit-isolines-an eccentric circle and an ellipse with deviation-are presented. The behavior of non-isotropic ground motion models has been described through an ideal and simple example, and the non-uniformity effect of the data recorded in different directions has been highlighted in the results of a non-isotropic ground motion model. This example clearly shows that the non-isotropic ground motion model exhibits better performance in estimating the acceleration in different directions, reducing residual variance and uncertainty. Finally, analyzing the actual data suggests that in the range near the epicenter, the results of the non-isotropic ground motion model are close to the results of other ground motion models, and as the distance increases, the difference increases, and this difference reaches twice to triple the initial value; however, analyzing the residual analysis shows that in the far distances, the non-isotropic ground motion model is also in good agreement with the data recorded at stations.