  We derive an effective theory on the orbifold branes of the Randall-Sundrum 1
(RS1) braneworld scenario in the presence of a bulk brane. We concentrate on
the regime where the three branes are close and consider a scenario where the
bulk brane collides with one of the orbifold branes. This theory allows us to
understand the corrections to a low-energy approach due to the presence of
higher velocity terms, coming from the Kaluza-Klein modes. We consider the
evolution of gravitational waves on a cosmological background and find that,
within the large velocity limit, the boundary branes recover a purely
four-dimensional behavior.
