According to the U.S. Geological Survey (USGS), the probability that a magnitude 6.7 quake will strike on any one of the San Francisco Bay area faults is 63 percent during the next 30 years. For comparsion, a magnitude 6.7 earthquake is equivalent to the 1994 Northridge, Calif., earthquake that killed 72 people and caused $12.5 billion in insured damages, according to the Insurance Information Institute (III).

Homeowners, condo and renters insurance policies do not cover damage caused by an earthquake, but coverage can be purchased as an endorsement or a separate policy. The cost of earthquake insurance varies from state to state. Contact your insurance agent to find out what the costs would be for your home.

Not surprisingly, Californians buy the most earthquake insurance, but earthquake insurance has been sold to residents of all 50 states. The South Carolina Earthquake Education and Preparedness Center at the College of Charleston says there is a 40 to 60 percent chance of a catastrophic quake somewhere in the eastern United States in the next 20 years. That has prompted the South Carolina Insurance News Service to recommend residents of that state consider purchasing earthquake policies.

The New Madrid seismic zone, which stretches from just west of Memphis into southern Illinois, also has insurers worried. Data from the USGS and the Center for Earthquake Research and Information at the University of Memphis now estimate that in the next 50 years an earthquake with an 8.0 magnitude could hit areas affected by the New Madrid seismic zone, causing widespread catastrophic damage.

According to the USGS, the San Andreas Fault has the highest probability of a large quake occurring in the next 30 years, at a likelihood of 59 percent.

Availability of earthquake coverage has become an issue in some regions of those states. For those who don't remember, which would include anyone not alive in 1811, an earthquake struck the New Madrid area with enough force to change the course of the Mississippi river and ring church bells on the east coast. In 2006, the Mississippi Department of Insurance Regulations required insurance companies to tell policyholders, in writing, about earthquake exclusions in homeowners policies before January 2007.

What does earthquake insurance cover?

Ideally, your earthquake insurance policy should cover the cost to replace or repair your damaged property. There are several options to consider when picking a plan, including:

• Does the policy cover only your dwelling? Are accessory structures, such as garages, also included?
• Will your policy pay for the contents of your home and for additional living expenses if your home is badly damaged or destroyed?
• Are there any exclusions or limitations to coverage?
• What deductible must you pay before the insurance kicks in?

How much does earthquake insurance cost?

Earthquake insurance rates are determined differently by each insurance company and can vary widely depending on several factors. Generally, older homes cost more to insure. Wood homes get better rates than brick buildings because wood tends to withstand quake stresses better. The III notes that premiums are based on the type of house, its age, the nature of the soil, and the proximity to recognized fault lines.

In addition, areas are graded on a scale of 1 to 5 for likelihood of quakes, and this is reflected in earthquake insurance rates. Because earthquake insurance is a type of catastrophic coverage, most policies carry a high deductible — anywhere from 2 to 20 percent of your replacement value of the structure. For instance, if the cost to rebuild your house after a quake is $100,000, and your policy has a 2 percent deductible, you would be responsible for the first $2,000.

Residents of California can buy insurance through the California Earthquake Authority (CEA). The CEA is a state-sponsored private-public partnership providing earthquake insurance to California homeowners, renters and condominium owners. At the end of 2007, the CEA had 775,000 policies active in the state — up by 2.8 percent from the year before. The 17 insurance companies that belong to the CEA offer a standard earthquake insurance policy with a 10 to 15 percent deductible. The CEA Web site has a tool to calculate your estimated annual earthquake premium. Californians can also buy earthquake policies outside the CEA.