How does one make a earthquake that affects physics objects?

Basically, a effect that's like this.

(Go to 0:12 in the video to see the earthquake )

Normally in a game like this you would make the ground immovable. Instead place it within a frame of immovable objects with a little wiggle room. Then each tick apply a small impulse to the ground, alternating between left and right.

Quick example dropbox.com/s/kn16gg550xy2qd6/EarthquakeDemo.c3p

Nepeo Thanks! It worked like a charm!