The impact of earthquakes, due to ground shaking, which affects the whole tunnel length from ovalingof the tunnel cross section, is investigated in this thesis. The influence of rock mass quality Q and thetunnel dimension is also studied. Finally, an approach to determine the new seismic support system usingexisting Q-system design chart and expected peak ground acceleration at the tunnel site is presented.The earthquake loading is modeled through quasi-static seismic loading in Phase2, a finite elementmodeling program by Rocscience, Inc. for design of underground structures and slopes. The quasi-staticassumption is valid in rocks, as due to their higher velocity, the wavelength of shear waves is > 20D,where D is tunnel diameter. At this scale, the dynamic interaction between the tunnel and the passingseismic waves is minimal and thus validates the quasi-static assumption. The seismic coefficient, aunitless vector dependent on the peak ground acceleration (PGA), serves as a representative parameterfor the expected critical earthquake.Four rock mass classes with Q = 1 - 40, to represent "very poor" to "very good" rock masses aremodeled by varying the deformation modulus and Mohr-Coulomb parameters, determined from empiricalrelations. The increase in support pressure (represented by axial force) is investigated as function ofrock mass quality Q and tunnel dimension.A model comprising of a 10 m diameter tunnel at 60 m depth surrounded by rock masses with Qranging from 1 - 40 is used to investigate the influence of rock mass quality Q. While the seismic loadingis unchanged, the magnitude of the axial force on the lining and the net increase due to seismic loading,referred to as seismic axial force, increases as the rock mass quality decreases.To check the influence of tunnel diameter, the diameter of a circular tunnel at 60 m depth and underfixed seismic loading is increased from 5 m to 20 m at 5 m interval. The magnitude of the axial force andthe seismic axial force increases with tunnel diameter for rock mass with Q = 1 ("very poor" rock mass).Conversely, the increase in magnitude of axial force and seismic axial force on the lining is relativelyinsignificant for rock mass with Q = 40 ("very good" rock mass).Inferred from the above findings, an approach to determine the seismic support pressure by using theconcept of Qseismic, first introduced by Barton (1984), is presented. During earthquakes, the requiredsupport pressure is expected to increase due to additional seismic load. However, this increase in supportpressure can be visualized as a decrease in rock mass quality Q around the tunnel and thus a new Q forseismic condition, called Qseismic = kQstatic, can be employed. The constant k mainly depends onthe seismic coefficient used to represent the PGA or intensity of the expected critical earthquake, androck mass quality. The relationship k = e Khwas determined for a 10 m diameter tunnel at 60 m depth for different rock masses. Kh is the horizontalseismic coefficient and the constant depends on the rock mass quality, i.e. 4.3 for Q = 1, 3.1 for Q =4 - 40, and 2.5 for elastic models. As Kh is increased from 0.05 to 0.70, k decreases from 0.81 to 0.06for very poor rock masses with Q = 1.The new seismic support system can be obtained using Qseismic from the existing Q-system tunneldesign chart. As a general trend, the increases in support pressure correspond to decrease in boltspacing and increase in the thickness of the fiber-reinforced shotcrete (Sfr). Unfortunately, the increasein thickness, which decreases the flexibility ratio, adversely affects the performance of the liner duringearthquakes and therefore other measures to increase the support pressure are recommended. Nonetheless,this approach results in a refined rule-of-thumb that incorporates rock mass quality Q and seismiccoefficient (= PGA) into the seismic design of tunnel support using Q-system.