Earth tremor

I need help with the understanding of a situation involving Earth Tremor

It says that the user is unaffected by the spell, which is almost like an earthquake.

What if allies or enemies would jump onto the user before they casted Earth Tremor?

Earth Tremor says it effects the ground. If the creatures are not on the ground, they don't take damage.

Quote from DxJxC >>

Earth Tremor says it effects the ground. If the creatures are not on the ground, they don't take damage.

 Keeping in mind "Whether a creature is a friend or an enemy, you can't willingly end your move in its space.”