Question

why does the maximum damage from an earthquake happens on the epicentre

Answer 1

The epicentre is the nearest point on the surface of Earth to where an earthquake rupture first occurs (known as the hypocentre).
As the seismic waves move away from the centre of the earthquake they begin to become attenuated (i.e. they lose energy with increasing distance of travel). As the nearest point on the surface is the epicentre, in general the earthquake waves will have retained the majority of their energy upon reaching this point and so in theory will be at their most destructive.

It should however be noted that the specific surface and near surface geology can also have significant impacts on the damage caused by earthquakes. In general hard rocks tend to undergo lower amplitude movements than that experienced in soft ground / soils. Also the liquefaction potential of soils means that significant differential settlements and loss of bearing capacity can occur during an earthquake. All of which can result in significant instability and or damage to buildings and other infrastructure.

Answer 2

Answer:

Greatest damage is caused closest to the epicentre because vibrations travel outwards from the epicentre and that the strength of the earthquake decreases away from the centre.