Frequency-dependent rupture behavior of subduction zone interplate megathrust faults has been observed by back-projection method in different frequency bands (from 0.05 to 5 Hz). It has been suggested that the down-dip region of the Tohoku megathrust radiated strongly at high frequencies ([10 Hz) compared with that of the up-dip region. By assuming the same source time function of each fault patch, we perform a synthetic sensitivity analysis to compare the energy received from the shallower parts (and further way from the receiver sites) with that from the deeper parts (and closer to the receiver sites) of the rupture. Our results indicate that regional onshore recordings are probably not adequate to constrain the presence of far-off shore high frequency radiations because of the strong  ttenuation of this region.