Two seismic arcs (150 km and 120 km long) located in the western Alps, 50 km apart from each other, are characterized by different statistical patterns in energy and space domains. For the two arcs, we found power-law distributions in energy domain with a lower b-value and fall-off for large events for the easternmost arc only, and roughly similar spatial damage. By comparing the shape and the statistical parameters of these distributions with those provided by numerical models of rock damage, we suggest a relatively more brittle behavior for one area with respect to the other. We discuss the implications of the observed distributions in terms of tectonics and of mechanics of faulting. We suggest three candidates to drive the relative changes in seismicity distribution between the two arcs: the earthquake depth, the host rock composition, and the inherited fracturing patterns.