The synthesizing process using the three components of the seismic wave to calculate the normal stress increment and shear stress increment acting on the sliding surface. (a) Transfer of the horizontal (EW and NS) acceleration components (aEW (t) and aNS (t)) to slope direction in horizontal plane (aHR (t)); (b) Transfer of the horizontal acceleration component (aHR (t)) along the slope direction and the vertical acceleration component (UD) (aUD (t)) to normal stress component (aNR (t)) and shear stress component (aSH (t)) acting on the sliding surface; (c) Obtaining the initial normal stress and shear stress (0, 0), and the increments of normal stress and shear stress acting (∆(t), ∆(t)) on the sliding surface by multiplying acceleration and mass of the soil column. is the angle between slope direction and the horizontal shaking direction of the earthquake; is the slope angle;
is unit weight of the saturated soil layer, and
is unit weight of the soil over the groundwater table; H is the depth of sliding mass.