Earthquake damage of underground structure indicates that the seismic response of tunnels is affected by the earthquake source, propagation medium, and local tunnel-surrounding rock system. Current research on the seismic response of tunnels primarily focuses on local tunnel systems, posing a challenge in comprehensively assessing the impact of earthquakes on tunnel group. This study introduces a theoretical seismological approach for the seismic response analysis of tunnels and presents a novel methodology for assessing the response. The proposed approach uses a kinematic seismic source as the earthquake source, assuming the geological strata as a layered medium and a tunnel as a point within a semi-infinite space. The wavenumber-integral method was used to solve for the seismic wave field and strain. To reflect the followability of underground structure to the surrounding rock deformation, we improved it and derived an analytical formula for the strain. The 2022 Menyuan earthquake was considered as a case study; the seismic damage to tunnels along the Lan-Xin Railway was analyzed using the proposed approach. The results confirm that there is a strong correlation between tunnel damage and free-field strain induced by earthquakes. The theoretical influence range of earthquake on tunnel was investigated using the diameter deformation ratio of the tunnel as an indicator. For tunnels embedded in a grade III rock mass, the theoretical range was approximately 7.0 km on both sides of the fault. For tunnels embedded in a grade V rock mass, the theoretical range can reach up to 25.9 km. The results also revealed that tunnels on the hanging-wall side of the fault had a more significant impact than those on the foot-wall side, although their affected areas were smaller.