"And behold, there was a great earthquake, for an angel of the Lord descended from heaven and came and rolled back the stone, and sat upon it. His appearance was like lightning and his raiment white as snow. And for fear of him the guards trembled and became like dead men" (Matthew 28:2-4).
This is the second earthquake Matthew describes as occurring during this weekend; the first (Matthew 27:52-54) was at the moment of Jesus' death. None of the other gospels report either one. Matthew, writing primarily for Jews, is using the images to emphasize the powerful importance of both the crucifixion and resurrection.
Metaphysically, the earthquakes represent the sense of upheaval we can expect as we move from our own crucifixions and resurrections. We are lifted to a higher dimension of consciousness, and we can be sure that circumstances will never be the same; the challenge that seemed to "crucify" us has lost its power over us (sometimes dramatically), and we are elevated in consciousness to a new reality.