  The IceCube detector allows for the first time a measurement of atmospheric
muon and neutrino energy spectra from tens of GeV up to the PeV range. The
lepton flux in the highest energy region depends on both the primary cosmic ray
composition around the "knee" and the contribution from prompt decays of mostly
charmed hadrons produced in air showers. It is demonstrated here that a direct
measurement of the atmospheric muon spectrum in the region above 100 TeV is
feasible using data that is already available.
