The Effect of Vertical Ground Motion in Dynamic Analysis for Near Fault Area in Yogyakarta

Abstract

Indonesia is surrounded by three major tectonic plates which are Indian-Australian, Eurasian and Pacific tectonic plates. Consequently, Indonesia is prone to seismic hazard. Horizontal ground motion has taken a major role in conducting nonlinear time histories analysis or in assessing liquefaction potential. However, for site near fault area, vertical ground motion can be quite significant and cannot be neglected. This paper aims to evaluate the effect of vertical ground motion in the near fault area by conducting dynamic analysis using MIDAS GTS NX. UBC Sand model is employed to model liquifiable material. Standard penetration test, laboratory test and downhole seismic tests are conducted at the site in order to characterize the shear wave velocities and properties of the soil at the area and to determine the thickness of the liquifiable layer. For this paper, two dynamic analyses will be conducted. For first analysis, only horizontal ground motion is applied to the model while in the second analysis, both horizontal and vertical ground motion will be applied. Based on dynamic analysis result, the horizontal surface motion and horizontal surface response spectrum that is propagated using bi-directional time histories will have bigger acceleration if being compared by only using horizontal time histories.