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The Seattle-area 6.8 earthquake and smaller aftershocks sent Mother Nature's latest resounding message about seismic activity -- not only is it difficult to predict where the earth will move, predicting when the shaking will occur isn't easy.

Washington State residents haven't been that shaken since 1949, when a similarly powerful quake struck a location almost identical to the Feb. 28, 2001 rumble 30 miles under ground, according to the U.S. Geological Survey. More recently, in 1965, the region experienced a quake rated at 6.5.

A quick, sharp jolt along the Calaveras Fault east of San Jose, CA shook that area to tune of 4.4 just days earlier on Jan. 25 and was followed by a smaller 2.1 aftershock.

Because no other natural disaster strikes with so little warning -- in time or place -- a perpetual state of preparedness is crucial if you live in a region rife with fault lines. Along with the Pacific Northwest, the U.S. Federal Emergency Management Agency says most at risk, facing a "very high" seismic hazard are California, six western states, Puerto Rico, the U.S. Virgin Islands and American Samoa. Ten states, including those in the New Madrid Fault region in the Middle South, contain areas with "high" seismic hazard.

Quake Preparedness

Residents in those areas should be familiar with the Red Cross' recommended earthquake preparedness and planning measures.

Some 17,000 Seattle area residents suffered power outages, but those with survival kits likely fared best. The kits, stored in an area near, but outside a home (say in your car trunk) for easy access following a quake, should include a few days of food, water and first aid, extra clothing, a battery-powered radio, flashlight, and other items.

Earthquake area residents should also consider earthquake insurance, which typically is not included in a basic homeowners policy.

In some areas the cost of quake insurance could be cost prohibitive and experts say the money may be better spent shoring up your home to better withstand a quake.

Wood-frame structures, when properly constructed, are designed to give and roll with a quake's punches, making homes one of the safest places to weather a quake.

However, older homes, newer ones with deteriorating foundations and those with structures prone to seismic damage, can be a disaster waiting to happen.

If you retrofit your home to better withstand the forces of a quake, not only will you improve its ability to withstand the forces of an earthquake, but you could also be eligible for special construction loans and grants as well as reduced insurance rates.

Earthquake power strikes a home in two ways: with thrusting, lateral or side-to-side motion and with rocking, rolling, uplifting action. The combination can literally throw a home off its foundation.

Bolt it down

To protect against lateral and uplifting movement, your home's framing should be bolted to its foundation.

If your home was built after 1950, there's a good chance it's bolted down, thanks to building codes in quake prone areas. Still, it may require some strengthening if it has experienced termite or moisture damage that may have weakened the connections.

If you aren't sure if your home is bolted to its foundation, crawl, stoop or walk under your home and take a peek. If it doesn't have a crawl space, look at the foundation connections in your garage, utility closet or other room with unfinished wall framing.

Otherwise, you may have to remove a portion of the dry wall to inspect. If it's bolted in the garage, it's likely the rest of the home is bolted.

Framing is typically bolted to the foundation at the sill, the lowest point in the wood frame. Engineers recommend expansion bolts fastened into the sill plate at intervals of six feet or less.

Also, "hold downs" (heavy metal brackets) can be bolted to the ends of structural wall framing to protect against uplifting energy.

Where you can't reach areas to bolt the foundation, you can use foundation brackets and anchors nailed to the mud sill and then bolted to the side of the foundation.

Cripple Walls

To further protect against lateral movement, shore up unsupported cripple walls. Also called "pony" walls, the structure sits between the first floor and the foundation and generally surrounds a large crawl space, basement or garage. It should be reinforced with shear walls -- plywood properly installed on the inside, to prevent the wall from buckling and folding over on its foundation.

Hardware and retrofitting plans are available for attaching the first floor to the foundation and the cripple wall as well as for fastening together multiple stories, shoring up "soft story" construction (decks, garages and other open areas beneath closed in areas) and strengthening pier construction.

Chimneys and Masonry

The inherent rigidity of chimneys, masonry walls and larger masonry structures -- such as homes in the New Madrid Fault region in the Middle South -- makes them more susceptible to seismic-related damage. Among the first images of damage from the Seattle area quake were crumbling masonry structures including the Washington state capitol building.

Strengthening and repairing such structures requires the expertise of a mason or other likewise experienced contractor familiar with masonry and masonry strengthening materials.

Structural strengthening almost always requires building permits and it is prudent to choose a licensed contractor experienced in seismic retrofitting.

Keep documentation of the project to show future buyers. You may have to disclose the work, which might also help increase the value of your home.

Quake Resources

  • The U.S. Federal Emergency Management Agency opened a special Seattle-area earthquake page to provide earthquake mitigation, preparedness, awareness and assistance information.
  • Association of Bay Area Governments' Earthquake Maps and Informationprovides links to numerous quake-related sites and information, including retrofitting, mitigation, loans and grants, insurance, and related services.
  • Homeowner's Guide to Earthquake Safetyis the California Seismic Safety Commission's quake country handbook for home owners.
  • The California Earthquake Authority and Insure.comoffer information about quake insurance.
  • Center for Earthquake Research and Information reveals California isn't the nation's only quake-prone region. The Middle South's New Madrid Fault and non-Californian quake information is available here.
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