Slip on a subduction megathrust can occur during an earthquake or aseismically. The size, location and frequency of earthquakes that a megathrust can generate depend on where and when aseismic creep is taking place, and what fraction of the long-term slip it accounts for. Here this issue is addressed by looking at the central Peru megathrust, and specifically at the Pisco earthquake of 2007. The findings show that aseismic creep accounts for 50–70% of the slip budget on the seismogenic portion of the megathrust