# Effect of Characteristics of Ground Motion on Seismically Induced Sliding Surface of Slopes
## 4 Results
### Effect of Slope Angle and Soil Properties  
The results presented in the previous section are calculated for the baseline characterizations (Case 9). The effect of the input ground motion may depend on the slope characterization, the parameters of which include the slope angle and soil strength parameters. The results of all simulations performed in this study are summarized in Figure 9. The difference between the surfaces determined from the dynamic and pseudo-static analyses are quantified with the residual, which is defined in the previous section. It should be noted that a positive residual means that the failure surface determined from the dynamic analysis is wider and the mobilized mass is larger. The calculated residuals could serve as a quantitative index for evaluating the performance of the pseudo-static analysis to estimate the failure surface.  
Figure 7: Determination of critical failure surface for Case 11 and Ofunato motion scaled to PGA = 0.25 g.  
Figure 8: Effect of input motion on the slope failure surface for Case 09: (**a**) Whittier Narrows; (**b**) Northridge; (**c**) Ofunato; (**d**) Kobe.  
For the Whititier Narrows and Northridge motions, the effect of the intensity is negligible for slopes inclined at 25\({}^{\circ}\) and 35\({}^{\circ}\). The influence of the soil strength parameters is also not shown to be consistent. The range of residuals lies between 0 to 0.4. For the steepest slope with an inclination angle of 45\({}^{\circ}\), both motions show a decreasing trend with an increase in the intensity. The cause for this characteristic is the widening of the pseudo-static-based surface with an increase in the intensity, as presented in the previous section. For the Ofunato motion, the trend is consistent with two motions with shorter mean periods for the slope angled at 25\({}^{\circ}\). For the 35\({}^{\circ}\) slope angle, the residual increases with intensity for Case 8, for which the strength is the highest. It is considered that the stronger soil resists premature failure and produces wider sliding surface. For cases with lower strengths, the intensity is demonstrated to have marginal influence. For the slopes inclined at 45\({}^{\circ}\), fluctuations in the outputs are observed. In general, the residuals tend to increase with intensity, although the influence is marginal. For the Kobe motion, the influence of the ground motion intensity is most clearly observed. An increase in the intensity of the ground motion causes a widening of the sliding surface, and corresponding increase in the residual. Even for slopes inclined at 25\({}^{\circ}\) and 35\({}^{\circ}\), this pattern is well visible. The residuals are highest for the steepest slope. It should be noted that the trend of the residual with intensity is different for 45\({}^{\circ}\) slope. For the Whititer Narrows and Northridge motions, which have shorter mean periods, the residuals decrease with intensity. For the  
Figure 9: Residuals of failure surface: (**a–c**) Whititer Narrows (**d–f**) Northridge (**g–i**) Ofunato (**j–l**) Kobe.  
Ofunato and Kobe motions, for which the mean periods are longer, the residuals increase with intensity, producing an inverse trend.  
The comparisons highlight that for slopes with inclination angles less or equal to 35\({}^{\circ}\) subjected to motions with mean period shorter than 0.3 s, the residual between the sliding surfaces determined from a pseudo-static and dynamic analyses are not significant. However, for steep slopes and motions with a mean period of longer than 0.3 s, the residuals become non-negligible. For such cases, it is recommended to derive the failure surface directly from a dynamic analysis rather than a predefined surface calculated from a pseudo-static analysis.