Today's Great Southern California ShakeOut earthquake drill will ask citizens to prepare for a giant earthquake on the southern San Andreas fault. The drill simulates a magnitude 7.8 event rupturing from south to north and focusing its energy into the southern California population centers.
But what if instead, the fault were to rupture from north to south? The Southern California Earthquake Center has modeled that possibility. Much of the energy still ripples through southern California but the model [right, top: surface cumulative peak velocity of a NW-SE rupture along the southern San Andreas fault. Credit, So. Calif. Earthquake Center - SCEC] shows the shock waves rolling across the border through Yuma and apparently across Arizona. I say apparently because the model stops just over the border. Watch the TeraShake simulation video [bottom left] side by side with a north to south rupture model [bottom right] at the SCEC website. We don't know how bad the shaking will be for most of the 5 million residents of southern Arizona.
The other concern I have about California's earthquake planning is the presumption that everyone will stay put after a major earthquake and wait for help to come to them. When I questioned my colleagues there about the possibility that residents cut off from food, water, energy, housing, etc, might become refugees and flood into Arizona, I was told that won't happen so it is not being planned for. Does that bring up visions of Hurricane Katrina to you? It certainly was my immediate reaction. Could Kingman, Yuma, Phoenix, and Tucson be inundated with streams of refugees looking for shelter and safety?
Since there will be ongoing large, potentially damaging aftershocks following a major rupture of the San Andreas, there may even be a bigger refugee movement than in the aftermath of a single event like a hurricane.