One nearby enemy
Charisma + Level vs. PD
3d6 + Charisma thunder damage, and the first enemy that hits you with a melee attack before the start of your next turn takes 2d6 thunder damage. (An empowered spell does not double this aftershock damage.)
Damage equal to your level.
5th Level Spell:
5d6 damage; 2d6 aftershock damage.
7th Level Spell:
7d6 damage; 3d6 aftershock damage.
9th Level Spell:
9d6 damage; 4d6 aftershock damage.
The spell's aftershock damage is now also doubled when echoing thunder is empowered.