The effects of low-velocity layer and basin topography in near-field ground motion amplification

Near-field ground motion amplification at sedimentary basins is widely observed and crucial to the earthquake hazard assessment. However, the effect of basin topography coupling with the low-velocity layer (LVL) in the ground motion amplification is yet to be fully understood. By constructing 3D basin models with surrounding mountain terrains and performing ground motion simulations, we compare the ground motion characteristics with different basin LVL depths and LVL velocities. The velocity contrast between LVL and bedrock controls the amplification magnitude. The maximum amplification area in the model changes from the central part to the periphery part of the basin with the velocity contrast decreasing and can be greatly influenced by the distance between the source and the basin. Amplification also spreads along the mountain edge circling the basin. Our work sheds light on the distribution of amplification within sedimentary basins surrounded by mountains, revealing that the velocity contrast between the LVL and bedrock plays a pivotal role in controlling the magnitude of amplification.