Earthquake is armor-piercing, so with protection above 15, mages should only rarely die. Thus, Stoneskin should protect a mage and all his communicants, and Ironskin should ensure that none of them even receive afflictions. Personal Regeneration (during Communion) would help with afflictions too. Other similar spells (like Bone Grinding) can be avoided by ethereality (and probably luck), but I can only assume Earthquake is the same. If there's a single Earthquake, Twist Fate should solve the problem.
I just tried to cast Earthquake for the first time in a MP game, and failed (mage killed by fliers before casting)
Too bad, it would've been really nice...