Comprehensive assessment of ground motion amplification in stratified soils with different layer configurations and types

This study investigates the seismic response of thirty meter deep soil profiles with varying compositions and layering sequences, including homogeneous clay and sand profiles and partially layered profiles composed of 22.5 m of clay over 7.5 m of sand, 7.5 m of clay over 22.5 m of sand, 22.5 m of sand over 7.5 m of clay, 7.5 m of sand over 22.5 m of clay, and evenly layered profiles with 15 m of clay over 15 m of sand or 15 m of sand over 15 m of clay. Nonlinear one-dimensional ground response analyses were performed using RSSeismic software, applying seven strong ground motions scaled to peak ground acceleration levels of 0.10 g, 0.25 g, and 0.50 g. The results demonstrate that seismic amplification is strongly governed by the soil type located at the ground surface, impedance contrasts between adjacent layers, thickness distribution of soft and stiff materials, and nonlinear stiffness degradation under increasing shaking intensity. Profiles with clay at the surface consistently produce higher amplification and longer period response because of greater modulus degradation, whereas sand dominated surfaces generate stronger short period amplification with reduced nonlinear softening. In partially layered profiles the largest amplification, approximately 5.67, occurred when a thin clay layer overlies thick sand in Profile 06, while the lowest amplification, between about 1.36 and 1.88, occurred in profiles with thick sand at the surface such as Profile 04. Deamplification zones were also identified, varying across profiles and shaking levels. These observations highlight the critical importance of accurately characterizing soil stratigraphy for reliable site-specific seismic hazard assessment and earthquake resistant design.