<p>Underground railway tunnels are essential for urban transportation, yet they are significantly vulnerable to seismic forces, particularly in weak rock conditions. Ensuring their resilience and structural integrity during and after earthquakes is critical for operational safety and continuity. This study investigates the seismic behaviour of railway tunnels embedded in weak rock masses using a computational approach employing a novel viscoelastoplastic rheological model. The model simulates the dynamic response of the surrounding weak rock under earthquake loading, with lateral seismic forces determined via a pseudo-static method. A case study is conducted using field measurements from the Jinpingyan Tunnel, a high-speed railway tunnel situated in a seismically active region with weak rock. Parametric studies evaluate the influence of key factors, including rock mass density, primary wave (dispersion) velocity, and tunnel geometry. The study highlights the depth-dependent nature of seismic response and indicates that the tunnel geometric properties substantially impact stress distribution and deformation. This research presents a straightforward, rapid, and practical approach for evaluating the seismic vulnerability of tunnels in weak rock, offering valuable insights for optimising tunnel design and material selection to enhance the seismic resilience of underground railway systems in earthquake-prone areas.</p>