When the character casts earthquake, an intense but highly localized tremor rips the ground. It knocks creatures down, collapses structures, opens cracks in the ground, and more. The shock lasts for 4 rounds, during which time creatures on the ground can't move or attack. Spell-casters will automatically be disturbed and lose any spells they attempt to cast despite of any types of magic resistances. The exact effects depend on the terrain and its features:

Cave, Cavern, or Tunnel: The spell rains down bits of the roof, dealing 8d6 points of damage to any creature caught under the cave-in (a saving throw halves this damage). Magic resistance in this case is bypassed as the spell doesn't affect the creatures directly. An earthquake cast on the roof of a very large cavern could also endanger those outside the actual area but below the falling debris.

Open Ground: All creatures standing in the area must make saving throws against spells or fall down. Fissures open in the ground, and every creature on the ground has a 25% chance to fall into one (a successful saving throw negates this effect) At the end of the spell, all fissures grind shut, killing any creatures still trapped within.

Structure: Most structures standing on open ground collapse partially, dealing 8d6 points of damage to those caught within or beneath the rubble (a saving throw halves this damage).

River, Lake, or Marsh: Fissures open underneath the water, draining away the water from that area and forming muddy ground. Soggy marsh or swampland becomes quicksand for the duration of the spell, sucking down creatures and structures. Creatures must make saving throws or sink down in the mud and quicksand. At the end of the spell, the rest of the body of water rushes in to replace the drained water, possibly drowning those caught in the mud.