Seismic Performance of Modal Transfer Stations on Soft Clays

In densely populated urban zones, seismic performance evaluation of strategic infrastructure during seismic events has become more challenging because the distance between surface and underground structures has been shortened to optimize the urban environment functionality. This is even more important in transit transfer stations, which usually comprise tunnels, bridges, and buildings, in which wave propagation interference is exacerbated. This paper explores the seismic interactions between on-ground and underground structures in soft-soil environments, focusing on a typical urban modal transfer station in Mexico City. The study is conducted through comprehensive parametric analyses using 3D numerical simulations in FLAC3D (v.6.0), considering both intraplate and interplate earthquakes, to assess the effect of differences in their frequency content, duration, and intensity. Multiple scenarios are considered in the numerical study, and the relative distances among the structures are varied to investigate both detrimental and beneficial interaction effects, and to identify the zone of influence where this interaction leads to ground motion variability. The study¿s findings established the key variables in the interaction between underground and on-ground structures, providing valuable insights into the seismic design and retrofitting of urban infrastructure in densely populated areas. © 2025 by the authors.