Zenith distribution of atmospheric neutrino events and electron neutrino mixing

Assuming atmospheric neutrino oscillations with dominant νμ↔ντ transitions, we discuss how subdominant νe mixing (within the Chooz reactor bounds) can alter the zenith distributions of neutrino-induced electrons and muons. We isolate two peculiar distortion effects, one mainly related to νe mixing in vacuum and the other matter to oscillations, that may be sufficiently large to be detected by the SuperKamiokande atmospheric ν experiment. These effects (absent for pure two-flavor νμ↔ντ transitions) do not vanish in the limit of energy-averaged oscillations.