Earth shock rarely silences AND kills anything. It can be really good against a few cards like Twillight Drake (which sees very little play), leper gnome, and argent horserider. It won't kill things like mad scientist without spell power. You can silence bigger things like shredder, belcher or sylvanas, but you won't outright kill them so you usually spend at least 2 cards to kill a minion which leaves you with a card disadvantage and shaman has very poor draw mechanics. But if you want to run silence it's probably just better to run spellbreaker because at least you get a decent sized body with the silence effect.