  A variety of new physics models allows for neutrinos to up-scatter into
heavier states. If the incident neutrino is energetic enough, the heavy
neutrino may travel some distance before decaying. In this work, we consider
the atmospheric neutrino flux as a source of such events. At IceCube, this
would lead to a "double-bang" (DB) event topology, similar to what is predicted
to occur for tau neutrinos at ultra-high energies. The DB event topology has an
extremely low background rate from coincident atmospheric cascades, making this
a distinctive signature of new physics. Our results indicate that IceCube
should already be able to derive new competitive constraints on models with
GeV-scale sterile neutrinos using existing data.
