Hopscotch Pattern of Destruction Is Found : Aftermath: Quake causes $1 billion in damage to Valley structures. Some areas are relatively unscathed.

The Northridge earthquake created a hopscotch pattern of destruction, hammering neighborhoods as far away as Sherman Oaks but sparing densely packed rows of apartment buildings much closer to the epicenter.

Altogether, the quake caused more than $1 billion in structural damage to the San Fernando Valley, half of the estimated total citywide. About 5,300 Valley structures were damaged, including 3,600 single-family homes, 285 condominium buildings, 842 apartment buildings and about 570 non-residential structures, according to city records.

But some communities fared much better than others.

Damage estimates in adjacent ZIP codes vary dramatically throughout the Valley, according to a Times computer analysis of Los Angeles Department of Building and Safety lists of structures rendered unsafe, or safe only for limited use.

Why the damage was greater in some neighborhoods miles farther from the epicenter is the big question facing scientists.

“Those questions will be answered, but you must be patient,” said Mihailo Trifunac, a USC professor of civil engineering. “Obviously, the damage was where the motion was severe.”

Building construction, soils, geography--even luck--may account for wide differences in damage suffered by Valley neighborhoods during the Jan. 17 earthquake.

Trifunac said there may also be some discrepancies in the damage estimates because of differences in judgment among city inspectors. Many were hired temporarily from municipalities across the country to help tally the damage.

Even so, scientists say it may take months or years to understand why the 6.8-magnitude earthquake caused at least $160 million in damage to Sherman Oaks, but only a tenth as much to high-density neighborhoods east of the San Diego Freeway and much closer to the earthquake’s epicenter.

The communities of North Hills, Panorama City, Arleta and Van Nuys--identified by ZIP codes 91343, 91402, 91405, 91411 and 91401--were not even among the 20 hardest hit in the Valley, although the areas are much closer to the quake’s epicenter than Sherman Oaks.

With few exceptions, the neighborhoods north of Magnolia Boulevard and east of the San Diego Freeway were spared the worst damage.

As expected, the most destruction was in Northridge, where building inspectors have so far estimated a total repair cost of $163 million to homes and businesses in the 91324 and 91325 ZIP codes.

At least $150 million more will be needed to fix buildings on the Cal State Northridge campus, bringing the Northridge damage total to more than $300 million.

But less than two miles east of CSUN, in the North Hills ZIP code of 91343, damage is estimated to be under $10 million.

About three miles north of CSUN, however, in the Granada Hills ZIP code of 91344, damage has been estimated to be more than $70 million.

Thomas L. Henyey, a geology professor at USC’s Southern California Earthquake Center, said one reason the quake may have caused such havoc in Sherman Oaks is because of proximity to the Santa Monica Mountains.

The amplification effect of thinning sediments may be to blame, he said. The closer to the mountains, the thinner the underlying sediment, causing the force of the earthquake to become more focused, he said. The result, usually, is more shaking on the surface.

But Henyey said more information is needed to explain the pattern of destruction.

“A whole variety of factors cause the ground to shake differently; the force doesn’t radiate evenly,” he said. “As the waves travel through the earth, it is like a hall of mirrors and lenses, where forces can be focused and defocused, amplified in certain places.”

Damage in the 91367 ZIP code of Woodland Hills is estimated to approach $30 million. But south of Ventura Boulevard in the same area, in neighboring ZIP code 91364, city inspectors estimate about $10 million in damage.

Encino neighborhoods in the 91436 and 91316 ZIP codes escaped, in comparison to Sherman Oaks, with only $6 million in damage. But Tarzana’s 91356, just west, sustained an estimated $13 million in damage.

Also hard hit was the Chatsworth ZIP code of 91311, the high-tech industrial center of the Valley, with nearly $50 million in damage.

As a result, many research and development firms there are fleeing to available space in eastern Ventura County, said Jeffrey M. Woolf, vice president of Beitler commercial realty services.

“I predict that most would come back, but some won’t,” Woolf said.

David Keim, principal inspector for the Department of Building and Safety, said that for all the damage to buildings--totaling about 61,000 structures--only half a dozen or so buildings have been ordered demolished.

But about 11,000 structures citywide have sustained enough damage to warrant immediate repair, city records show.

About 9,000 of those are posted with yellow notices, which allow limited use, and 2,000 have red notices, which means that they are unsafe to enter. Commercial buildings account for 1,000 of the yellow-tagged buildings and about 500 of the red, Keim said.

“In most cases, even red-tagged buildings are, in fact, repairable,” Keim said. “The variable will be cost. Owners have to decide whether it is worth it.”

So far, the city has issued 26 permits to rebuild, 848 to repair and 28 to demolish as a result of the earthquake, according to a report issued Monday by the Department of Building and Safety.

Richard O’Reilly, director of computer analysis for The Times, assisted with this story.

* VALLEY BRIEFING: A map breaks down Valley destruction by community. B2

Quake Damage by ZIP Code

San Fernando Valley ZIP codes ranked by earthquake repair cost estimates, as of Monday (nearest community in parentheses):

(In millions) 1 91330 (CSUN) $150.0 2 91423 (Sherman Oaks) $98.3 3 91324 (Northridge) $97.3 4 91344 (Granada Hills) $72.6 5 91325 (Northridge) $66.6 6 91403 (Sherman Oaks) $62.9 7 91311 (Chatsworth) $48.8 8 91335 (Reseda) $35.1 9 91303 (Canoga Park) $34.7 10 91367 (Woodland Hills) $27.8

Sources: Los Angeles Dept. of Building and Safety