Event Horizons of Numerical Black Holes
  We have developed a powerful and efficient method for locating the event horizon of a black hole spacetime, making possible the study of the dynamics of event horizons in numerical relativity. We describe the method and apply it to a colliding black hole spacetime. 
Peter Anninos, David Bernstein, Steven Brandt, Joan Masso, Edward   Seidel, Larry Smarr, Wai-Mo Suen, Paul Walker