Answer:
It is a phenomenon. Physically, before resonance elstic force (due to low frequency) balances most of the external force. At resonance damping force balances external force, when little damping is present then amplitude of vibration grows due to accummulation of engery in every cycle. After resonance inertia force (due to highfrequency) balances the external force. So even small damping could dissipate energy to build up large occilations similar to resonance conditions.
To answer mathematically, Please visit the equation for magnification factor vs frequency ratio. For very high frequency, the denominator part is very large (i.e., the inertia force becomes very large)which reduces the amplitude.
By:
Prof. S.K. Dwivedy Date:
20141224
