We on the East Coast just felt a magnitude 5.8 earthquake, so I went looking up the bracha to make on such an occasion. Apparently there are varying views; see <http://www.ou.org/torah/tt/5764/mishpatim64/specialfeatures.htm#7> for discussion. Blessed are you, Lᴏʀᴅ our God, King of the Universe, Whose power and might fill the world. --Chesky