These physical convulsions will be the earth's 'travail pains' as she labors to bring forth the New Creation of the Millennial Age.
Jesus said in Matthew, "In those days shall the sun be darkened (that is, its light obscured) and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens (the principalities and powers of the heavenly places, not the Powers and Kingdoms of the Earth), shall be shaken."