The aim of this study is to establish a simple method for evaluating the extent of damage to geogrid reinforced soil walls (GRSWs) subjected to earthquakes. Centrifuge tilting and shaking table tests were conducted to investigate the seismic behaviour of GRSWs, with special focus on the eŠects of the tensile stiŠness of the geogrids, the pullout characteristics and the backˆll materials. As a result, it was found that GRSWs showed large shear deformation in the reinforced area after shaking, that such deformation was in‰uenced by the tensile stiŠness of the geogrids, the pullout resistance and the deformation modulus of the backˆll material, and thatˆnally slip lines appeared. However, the GRSWs maintained adequate seismic stability owing to the pullout resistance of the geogrids, even after the formation of slip lines. It is considered that such slip lines appeared due to the failure of the backˆll material. Since the maximum shear strain occurring in the backˆll can be roughly estimated from the inclination of the facing panels, using a simple plastic theory, it is possible to evaluate whether the backˆll has reached its peak state or not. The formation of slip lines observed in the centrifuge model tests could be well explained by this method. Finally, the method is proposed to estimate the failure sections in the GRSWs using a Two Wedge analysis.