The tragic deaths of two central California residents struck by debris falling from an aged masonry building points to the insidious danger lurking in such 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, 2003, 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, according to reports.

The Acorn Building, was a more than 100-year-old community landmark constructed with wood framing and unreinforced masonry. The building was upgraded and renovated, but never seismically retrofitted.

A swarm of more than 600 aftershocks with nearly 100 of them a magnitude of 3.0 or greater likely further added to the instability of other unreinforced masonry buildings in the area.

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 safety construction.

"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.

Within 24 hours of the disaster, Gov. Schwarzenegger visited Paso Robles and other areas suffering quake damage to declare a state of emergency to open a flow of funds to help begin rebuilding the central California town of some 27,000 residents.

The Acorn Building building may have to be demolished.

Most homes are constructed of more seismically-fit wood-frame construction, but older homes in the area and others prone to seismic activity were built without seismic building codes and could suffer fates similar to masonry buildings should a stronger quake hit.

Unrelated to the Central California quake, 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: 2003-2032," a report issues by the U.S. Geological Survey (USGS).

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 you for loans, grants and reduced insurance rates.

  • Bolting your home to its foundation at the sill -- the lowest point in the wood frame -- helps it stand up to quakes' 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 your 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.
  • Also, 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 contractor to inspect and retrofit, often with re-bar and other metal-laden materials.

    The Oakland, CA-based Association of Bay Area Governments (ABAG) offers "Residential Quake Safety Quiz" which lets you determine the potential seismic threat to your home 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 by residents who live in single-family homes, apartments, condos, townhomes and manufactured homes. The test score comes with advice for those who live in homes most susceptible to quake damages. The website also offers additional information on earthquake preparedness.

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