Attenuation of ground-shaking with distance and across different geological units and tectonic regions is of great importance for reliable and accurate ground-motion prediction. In this work, we investigate the differences in ground-motion attenuation across the Mexican subduction zone by comparing observational constraints with new numerical modeling results. Tejeda-Jacome and ChavezGarcia (2007) reported significant variation in seismic motion attenuation for two paths perpendicular to the Mexican Pacific coast: Guerrero and Colima. Their models predict stronger ground motions for hypocentral distances larger than 100 km for the northern section of the subduction zone (Colima) than for the southern section (Guerrero). We test these findings, considering two possible explanations for the observed differences: (1) differences in the subducting slab geometry between Colima and Guerrero; (2) variable shallow structure of the overriding plate due to the presence of the Trans-Mexican Volcanic Belt (TMVB) that strikes obliquely to the Middle American trench. We conduct 2D P-SV pseudo-spectral numerical simulations to investigate which of the two hypotheses better explains the observed attenuation properties. We find that the TMVB, closer to the coast in Colima area, better describes the differences in attenuation perpendicular to the Mexican subduction zone. These findings will be important for local ground-motion prediction for seismic hazard studies.