Charles Ellicott Commentary Matthew 28:2

"And behold, there was a great earthquake; for an angel of the Lord descended from heaven, and came and rolled away the stone, and sat upon it." — Matthew 28:2 (ASV)

The words imply that they did not witness the earthquake, but rather inferred it from what they saw. The form of the angel is described in Mark 16:5 as a young man in white or bright (Luke 24:4) clothing. This was the answer to the question they had been asking as they came: Who shall roll away the stone for us? (Mark 16:3). That task would have been beyond their strength.