It was common opinion that earthquake effects on underground structures are not very important. This is because these structures have generally experienced a low level of damage in comparison to constructions above ground. Nevertheless, in the urban areas the serviceability of underground networks (like roadway, railway, water and gas pipelines) were severely interrupted and limited after strong earthquakes and the seismic response of these structures have been addressed by many authors in the last years. The objective of this research is directed towards numerically investigating the seismic behaviour of the Greater Cairo metro line No.4 passes under the River Nile in Egypt land and evaluate the additional forces due to increasing seismic loads on this horizontal twin tunnel. For this purpose, 2D nonlinear dynamic analyses of soil–structure system are carried out with the aid of finite element software, PLAXIS 2D. The evaluation is done by modal analysis, with a numerical model of the tunnel, based on the finite element method. Finally, this study can set new guidelines for the design phase of an underground structure and address the effects of earthquakes on tunnels to protect it from damage caused by ground shacking.