  The equilibration of matter and onset of hydrodynamics can be understood in
the AdS/CFT context as a gravitational collapse process, in which "collision
debris" create a horizon. In this paper we consider the simplest geometry
possible, a flat shell (or membrane) falling in the holographic direction
toward the horizon. The metric is a combination of two well known solutions:
thermal AdS above the shell and pure AdS below, while motion of the shell is
given by the Israel junction condition. Furthermore, when the shell motion can
be considered slow, we were able to solve for two-point functions of all
boundary stress tensor and found that an observer on the boundary sees a very
peculiar $quasiequilibrium$: while the average stress tensor $<T_{\mu\nu>}$
contains the equilibrium plasma energy and pressure at all times, the spectral
densities of the correlators(related with occupation probabilities of the
modes) reveal additional oscillating terms absent in equilibrium. This is
explained by the "echo" phenomenon, a partial return of the field coherence at
certain "echo" times.
