No one who lives in Southern California has yet experienced a "great earthquake" on the San Andreas fault like the ones that recur through history at regular intervals, UC Irvine professor Lisa Grant Ludwig just noted on KPCC's Patt Morrison. She reminds us that the Northridge quake that did so much damage in Los Angeles on Jan. 17, 1994 was "moderate." Ludwig, by the way, studies environmental problems with an emphasis on natural hazards and says that with an eye toward the after effects of the big quake that's coming — think Katrina on steroids — she keeps an extra supply of water in her home. Just saying.