Dynamics of Apparent and Event Horizons
  The dynamics of apparent and event horizons of various black hole spacetimes, including those containing distorted, rotating and colliding black holes, are studied. We have developed a powerful and efficient new method for locating the event horizon, making possible the study of both types of horizons in numerical relativity. We show that both the event and apparent horizons, in all dynamical black hole spacetimes studied, oscillate with the quasinormal frequency. 
Peter Anninos, David Bernstein, Steven Brandt, Joseph Libson, Joan   Masso, Edward Seidel, Larry Smarr, Wai-Mo Suen, Paul Walker