<p>The dynamic response degree of underground structures is closely related to unfavorable geological structures (e.g., faults, large discontinuities, etc.), which are frequently the focus of seismic fortification of tunnel structures. Existing studies have paid attention to the effects of inactive or active faults on the seismic response of tunnels and analyzed their mechanical interaction mechanism. However, a more quantitative understanding of the dynamic behavior of tunnels crossing multiple faults from a probability perspective is still lacking. In the present work, a series of two-dimensional discrete element models (DEM) based on universal distinct element code (UDEC) is established to reveal the dynamic response of the deep-buried tunnels that traverse multiple faults (i.e., single fault, double-parallel faults, and cross-cutting faults). This study investigates the disparities in the internal force response of deep tunnels when subjected to harmonic loading. The analysis encompasses a quantitative discussion of the impact of fault dips and fault mechanical parameters on the seismic fragility curves of tunnels. The results obtained demonstrate that faults are responsible for the unsymmetrical distribution of internal forces of the tunnel lining, resulting in remarkable localized stress concentration. In special cases, faults with dips ranging from 45º to 75º for the cross-cutting fault model are particularly substantial. The number and spatial distribution of faults exert considerable effects on the seismic vulnerability of tunnels, exhibiting a nonlinear variation with the increment of fault dips. Furthermore, the influence of the internal friction angle of the fault on the seismic vulnerability of tunnels is more prominent than the shear stiffness and normal stiffness of faults. These findings could offer valuable insights for the future seismic design and construction endeavors of mountain tunnels crossing faults.</p>