As military helicopters ferry search and rescue teams over the Pacific Northwest, below them are scenes of devastation from a giant earthquake that could strike the region at any time. Tsunami waters surge through coastal communities. Buildings, bridges and roads lie in ruins. Fires burn out of control. Survivors are stranded on rooftops, cling to floating debris or are trapped inside wrecked buildings. Seismologists say a full rupture of a 650-mile-long offshore fault running from Northern California to British Columbia and an ensuing tsunami could come in our lifetime, and emergency management officials are busy preparing for the worst. Federal,...