Quake is a magic materia in Crisis Core -Final Fantasy VII- that casts a strong spell with a wide area of effect. Its rapid cast time and wide area of effect makes it one of the most powerful materia in the game, allowing Zack to clear enemies around him.
Obtained
Quake can be obtained earliest from Wutai Secret Shop, which is unlocked from the mission "M4-2-6: The Five Saints of Wutai", or through Materia Fusion.
Quake is a reward for "M5-4-5: Experiment No. 123", dropped by Grand Horn, and found in "M8-6-4: S.O.S.?", "M9-1-5: Behind the Scenes"
Buy: Bone Village Commerce
Graviga is a reward for "M1-3-5: Robots in the City", and found in chests in "M6-6-2: The Don's Second Secret", "M7-3-6: P's Precognition Lv. 6", "M7-6-6: The Determined Recruiter", "M8-5-6: Treasure Info 6", "M9-1-1: Underground Caves" , and "M9-2-1: The Third Power". Later, it can be purchased in Bone Village Commerce.
Use
Ability
Quake's main strength is its rapid cast time and wide area of effect. It can deal a significant amount of damage to enemies, but is dependent on Zack's MAG. In many areas, it can be used either as crowd control or to clear a group of enemies.
More often, Quake will not be Zack's main source of damage, because it is much more difficult to reach 99,999 damage. Rather, it is used to defeat enemies weakened by Graviga. In that regard, it serves a less risky, but less strong, role compared to Costly Punch.
Quake is most effective when combined with an equipped Dualcast materia, greatly improving its damage output. Due to its high MP cost, it should be paired with an accessory that reduces Zack's MP cost to zero, such as Soul of Thamasa or Genji Helm.
Materia Fusion
Quake is the highest level of its fusion table. Below it are Gravity, Graviga, and Darkness. Though Graviga is very desirable to have, Gravity and Darkness can mostly be discarded other than to fuse into Quake. Because of Quake's usefulness, it should be used to max one of Zack's stats, particularly his MAG stat to boost its damage.
Quake can be fused most easily with Libra to guarantee the fused materia will keep the Graviga spell, and then items used for fusion should be used to max stats. The PSP version also gives Zack the ability to gain 99 Phoenix Downs from Minerva in "M9-6-6: The Reigning Deity" to make this easier, while both versions grant mastered Digital Mind Wave materia with high stats earned from naturally completing the "M9: Great Cavern of Wonders" series that serve as a good starting point. SP can be easily obtained from Three Stars in "M9-5-3: Unusually Strong Monsters" to support fusion.