(Spell Compendium, p. 223)

Evocation [Earth]
Level: Druid 3, Cleric 3,
Components: V, S, DF,
Casting Time: 1 standard action
Range: Medium (100 ft. + 10 ft./level)
Area: 40-ft.-radius spread
Duration: 1 round/3 levels
Saving Throw: See text
Spell Resistance: No

When you cast this spell, a small, localized tremor shakes the ground in the area. Detritus and loose debris rattle with the small quake, and creatures caught in the area stumble and fall.

This minor quake is not strong enough to damage structures. The effect lasts for 1 round per three caster levels, during which time any spellcaster on the ground in the area must succeed on a Concentration check (DC 15 + spell level) or lose any spell she is casting. A creature attempting to use a skill that would provoke attacks of opportunity (such as Disable Device, Heal, Open Lock, and Use Rope, among others) must succeed on a DC 15 Concentration check, or the action automatically fails and is wasted. Each creature in the area must make a Reflex save each round or be knocked prone.