This article describes briefly the main assessments on the approaches used by engineers in quantifying the seismic effect on an underground structure, both referring to deterministic either probabilistic methods. However, the main purpose is that of proposing a new simplified approach to evaluate through numerical simulations the ovaling effect on the cross sections of tunnels. This method could be applicable not only to obtain closed form solutions for circular shapes, but also to acquire the stresses acting on the lining of tunnels characterized by complex geometries and non homogeneous ground conditions. Therefore, this study has the goal to propose a method that could be as more consistent as possible with the common procedures nowadays adopted to evaluate the effect of seismic motion on tunnels in a way that can be reliable for structures subjected to ground motion caused by a seismic event. Of course, the method cannot be apply to those conditions where a fault zone is close to the structure or they cross each other. After a short presentation of the theoretical approach followed, the paper deals with the case of Istanbul Metro line Kadikoy-Kartal and the T74R railway tunnel along the line from Dharam to Qazigund in Kashmir region of India.