This means every Lightning Shield charge AFTER 3 charges are included into your next Earth Shock.
Meaning that charges 4, 5, 6, 7, 8, and 9 will be added. Or to state it otherwise, 6 Lightning shield orbs maximum.
The Earth shock alongside a max of 6 charges will be concentrated into a single powerful Earth Shock dealing STAGGERING damage.
Every single lightning shield charge takes 33% of your total spellpower added to damage, meaning that a shaman with 5000 spellpower (maybe he had alot of procs etc) and 9 charges of Lightning Shield will deal 15199 nature damage before any modifiers! (and 30398 if it crits - WTF)
I can imagine glyphs, and improved shields affecting Lightning Shield as well!
Is affected by Elemental Fury, as in dealing 200% crit damage.
(taken from level 80 spells)
EDIT:
Note: Earth Shock damage is currently NOT included into the total damage of Fulmination (this might, or might not change in the future)
Earth shock will deal it's own damage, and all the Lightning Shield orbs are counted as Fulmination. Meaning that Casting Earth shock will trigger it, and deal damage, but will still be it's own source of damage.