Seismic patterns in two-dimensional multilayer sediments using a hybrid boundary-finite element approach

This study proposes a hybrid boundary-finite element approach for calculating the seismic response of multilayered surface sediments with arbitrarily shaped topography. The system is subjected to oblique incident SH waves of varying frequencies. The method begins by introducing the hybrid formulation, which is then developed for multilayered problems by enforcing displacement and traction continuity at the interfaces. The free-field motion is incorporated into the solution by accounting for incident and reflected wave components. The developed method is implemented in a computer algorithm, and its accuracy is validated by solving several seismic problems with known solutions. Finally, a parametric study is conducted, analyzing both single-layer and two-layer sediment systems over a base soil layer. The sediments feature triangular, semi-square, and semi-circular geometries under incident SH waves, and the resulting seismic amplification patterns are presented. The results showed that the average dimensionless amplification across all frequencies and incident angles was 1.16 for the triangular shape, 1.18 for the semi-square, and 1.16 for the semi-circular shape in the single-layer case. For the two-layer case, these values increased to 1.47, 1.73, and 1.30, respectively. Furthermore, the single-layer triangular and semi-circular sediments demonstrated a greater capacity to absorb and trap wave energy, preventing it from propagating into the underlying layers.