Omniscience vs Omnipotence?

Therein lies the oxymoron; if god is all knowing and causes everything then he knows what he will do in the future; so he must know that he will kill innocents (take the Japan earthquake which he could not prevent) so now we have the question; has he not the power to change his future mind? Apparently not, so that would mean he is neither omniscient nor omnipotent. So what we are left with is not a god but a big useless incompetent ghost.