While the aboveground threat from weather events is undeniably serious, it often pales in comparison to the threat from below. Earthquakes cause massive damage. The 1994 quake in Northridge, Calif., was the second-largest U.S. catastrophe with claims totaling $12.5 billion.

"The simple fact is, no area of California is immune from earthquakes,'' says Mark Leonard, a spokesman for the California Earthquake Authority. The organization, funded by premiums and member insurance companies, sells policies to the nearly 30 percent of state residents who have purchased quake coverage.

Private insurers in California are also required to sell their own policies if they don't participate in CEA, Leonard says.

But people living on the West Coast aren't the only ones that should be concerned about earthquakes. Residents of Missouri, Illinois, Kentucky, Tennessee and Arkansas also face a possible threat from shaky ground.  The New Madrid seismic zone runs across the five states where they border the Mississippi River.

Though not as infamous as California's San Andreas fault, the New Madrid zone has a 40 to 63 percent chance of causing a quake measuring 6.0 or greater on the Richter scale sometime during the next 15 years, according to the Center for Earthquake Research and Information at the University of Memphis in Tennessee.

Rather than purchase separate earthquake plans, residents in the New Madrid region usually obtain coverage as an endorsement to their standard homeowners policy, says Ruth Gastel of the Insurance Information Institute.