The tragic deaths of two central California residents struck by debris falling from an aged masonry building point to the insidious danger lurking in older structures.

In quake after quake, unreinforced masonry structures—from chimneys to walls to entire buildings—are among the first to go when mountain-building earthquake faults begin to stir.

When a central California thrust fault generated the magnitude 6.5 Central Coast Quake on Dec. 22, sections of the historic Acorn Building at 12th and Park streets in downtown Paso Robles collapsed. The roof pancaked—sliding onto a row of parked cars—and the second-story landmark clock tower disintegrated.

Two residents fleeing from their workplace—Ann's, a dress shop in the building—were killed in the falling debris. Jennifer Myrick, 19, of Atascadero, and Marilyn Zafuto, 55, of Paso Robles were later pulled from the rubble. The building, also called the Mastagni Building (for the owner), also housed Pan Jewelers, House of Bread, a bakery and coffee shop, and the Rose in the Woods souvenir and gift shop.

The Acorn Building was a more-than-110-years-old community landmark constructed with wood framing and unreinforced masonry. The building was upgraded and renovated, but never seismically retrofitted.

If some good can come from the two lives lost in the Paso Robles destruction, officials hope it's the lesson learned about unreinforced masonry buildings and older structures built without the benefits of seismic building codes.

"Here you can see very clearly the difference in a building that hasn't been retrofitted and one that has been retrofitted," said California Gov. Arnold Schwarzenegger as he toured Paso Robles, pointing to heavily damaged buildings on one side of the street and relatively intact structures on the other.

Gov. Schwarzenegger visited Paso Robles and other areas suffering quake damage to declare a state of emergency and open a flow of funds to help begin rebuilding the central California town of some 26,000 residents.

Most homes are constructed of more seismically fit, wood-frame construction, but older homes built without seismic building codes in active quake areas could suffer fates similar to those of masonry buildings should a stronger quake hit. And there is a growing chance that could happen.

There is a 62 percent chance of at least one 6.7 or greater quake before 2032 in the San Francisco Bay Area, according to "Earthquake Probabilities in the San Francisco Bay Region: 2003­2032," a report issued by the U.S. Geological Survey.

USGS and other quake-related agencies urge building and home owners to prepare for the "Big One" by shoring up the ability of their property to better withstand seismic activity. Eligible retrofits not only strengthen a home, but can also qualify for loans, grants and reduced insurance rates.

* Bolting a home to its foundation at the sill—the lowest point in the wood frame—helps it stand up to a quake's lateral energy. "Hold downs" (heavy metal brackets) can be bolted to the ends of structural wall framing to protect against uplifting seismic energy.

* Shore up cripple walls to further protect against lateral movement. Also called a "pony" wall, the cripple wall 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 during a quake.

* Hardware and retrofitting plans are available for fastening together multiple stories, shoring up "soft story" construction (decks, garages and other open areas beneath closed-in areas), pier construction and other weak points.

* The inherent rigidity of chimneys, masonry walls and other masonry structures—such as the old buildings in Paso Robles—make them more susceptible to seismic activity and require the expertise of a mason or other knowledgeable structural engineer or contractor to inspect and retrofit, often with rebar and other metal-laden materials.

The Oakland-based Association of Bay Area Governments offers an interactive "Residential Quake Safety Quiz" online at http://www.abag.ca.gov/bayarea/eqmaps/fixit/quiz/index.html. The quiz determines the potential seismic threat to a structure based on its proximity to a fault zone, existence of soft-story construction, age and height, building materials, and the building's footprint. The test can be used for single-family homes, apartments, condos, townhomes and manufactured homes. The score comes with advice for correcting any problems.

U.S. Geological Survey's "Earthquake Probabilities in the San Francisco Bay Region: 2003-2032" is available online at http://quake.wr.usgs.gov/research/seismology/wg02/.

Real estate writer Broderick Perkins, executive editor of San Jose-based DeadlineNews.Com, writes regularly for
Willow Glen Resident.