Tremor

A truly potent weapon, casting this spell will set off a horrible earthquake that will rumble the ground. The caster's foes will be frozen in terror, lose their footing and if falling rocks don't kill them, they will be swallowed by growing gaps in the ground, never to be seen again.

Tremor cannot be cast in settled areas, as it would cause death on a massive scale, so its use in such a way is thus strictly forbidden.