Seismic activity can compromise the stability of tunnels and tunnel intersections within fractured rock masses. Therefore, it is crucial to assess the impact of tunnel shape and rock joint characteristics on their behavior during seismic events. This study investigates the effects of different tunnel shapes on rock mass behavior during seismic excitation. The results indicate that block detachment predominantly occurs in the vicinity of the tunnel's crown region, particularly at the intersection of two tunnels. The larger tunnel, referred to as the main tunnel, undergoes minimal deformation, less than 0.3 meters, when subjected to seismic excitation with an amplitude of 0.36g. Conversely, the smaller access tunnel exhibits substantial block displacement, exceeding 5 meters, primarily near the intersection of the two tunnels. This behavior is attributed to intersecting rock joints near the tunnel intersection, coupled with favorable joint dip angles, which facilitate block detachment and sliding during seismic activity. The detachment of blocks results in the formation of sharp, cone-shaped failure wedges, indicating potential failures even in tunnels with a horseshoe-shaped cross-section. Square-shaped tunnels display significant joint yielding and detachment of larger blocks exceeding 25m³ in volume, while horseshoe-shaped tunnels yield smaller blocks with volumes less than 10m³ due to their geometry. Analysis of cyclic shear stress-strain loops reveals nonlinear rock behavior, with greater nonlinearity observed in areas experiencing higher shear strain. Regions distant from potential failure surfaces exhibit steeper loops, indicative of higher stiffness and lower damping, while regions near potential failure surfaces display flat loops, suggesting reduced stiffness and higher damping characteristics.