To understand our reaction in earthquakes, it is instructive to consider some of the expressions that we use in daily life, such as "solid as a rock". As an 3-yr old knows, the ground is the very definition of stability; certainly it is not supposed to go anywhere. Living in earthquake country, we have learned that the stability is an illusiion, created not by smoke and mirrors, but by the fact that human life spans are the merest blink of an eyelash in the majestic progression of geologic time. Those mountains that provide Southern California's dramatic backdrop? They have grown surely as a California redwood tree, and continue to grow to this day. They may lay dormant and apparently unchanging for a thousand years, their growth coming only in spurts we know as earthquakes.
During an earthquake such as last year's Northridge event, a fault moves for just a few seconds--really just a brief hiccup of adjustment. But the effect on our society belies that. Waves radiate in every direction from a fault plane, with different wave types traveling at different speeds and spreading out the energy one feels somewhere distant from the fault. The waves may get trapped within layers of sediment within basins or valleys, giving rise to reverberations that both prolong and amplify the shaking.
Size sexonds of fault rupture can thus translate into 20 billion dollars in property and infrastructure damage--an impact that can last as long as the aftershocks. The impact on our collective consciousness may also be long lasting.
It is possible to speak in terms of statistical odds: If you want to live in the United States, only in parts of Alaska will you find a higher probability of earthquakes than here in California.
Is it rational to factor earthquakes into a decision where to live? Of course it is; earthquakes are a reality, and the choice to live in California should be based on informed consent. We get mountains and beaches and 75-degree days in February; in exchange we accept the risks, and hopefully take the steps we can to mitigate the hazards.
Is it rational to run screaming from the state of California with only the clothes on ones' back? We don't think so. Statistically speaking, your odds of dying in an earthquake are probably lower than your odds of being killed on the freeway--and may well be comparable to your odds of being killed by a tornado in the Midwest or a hurricane in the South, or even a bee sting in Anytown, USA.