Earthquake is a Ground-type damage-dealing move.
It is also known as TM26—the nomenclaturally designated TM of this move.
Earthquake monofunctionally inflicts damage.
If the opponent is in the preparatory turn of Dig's two-turn execution, it will not only be vulnerable to Earthquake; Earthquake's attack power will also doubly improve.
Grassy Terrain will halve the attack power of Earthquake while it is operatively in effect.