Loma Prieta 30 years later: Santa Cruz rises from the rubble to become a model of earthquake preparedness

October 21, 2019

Santa Cruz — This week’s burst of earthquakes ended this city’s stretch of seismic calm, reminding residents of the 6.9 Loma Prieta temblor that almost destroyed it 30 years ago Thursday.

But downtown’s newest building never flinched.

Built in the hole that once held a beloved 1890s-era brick bookstore, the ambitious $35 million Park Pacific project is secured by a sunken array of stable columns, a two-foot deep concrete mattress, more flexible framing and other state-of-the-art engineering practices.

Reborn as a symbol of resiliency, this sunny coastal city is braced and bolted — a model of earthquake preparedness in a place that knows there will be future disasters.

“We are doing the best we can,” said city historian Ross Gibson, who grieves the loss of downtown’s countercultural charm yet welcomes the new structural engineering that will help save lives. “It is all a learning experience.”

All over the Bay Area, government agencies and private and nonprofit sectors have invested $73 billion to $80 billion in 700 structural retrofits and replacements to create a metropolitan area that could better withstand a Loma Prieta-size earthquake, according to the U.S. Geological Survey. On Oct. 17, 1989, that 6.9 temblor killed 63 people, injured more than 3,700, destroyed 366 businesses and 11,000 homes and caused $6 billion in property damage.

Hospitals are sturdier. Elevated freeways and bridges offer better support. Major water pipes now bend, not break. Natural gas pipelines have earthquake-resistant electrical equipment, spring-like metal transmission lines and automatic shut-off gas valves in fault areas.

To be sure, some projects still await completion. BART will finish its new “slinky” version of the six-mile-long Transbay Tube retrofit by fall 2022. On the main suspension span of the Golden Gate Bridge, a retrofit is being designed, with construction completed by 2026.

In addition, 7,801 buildings remain unretrofitted and at significant risk of collapse in the state’s highly seismic regions because of ineffective or non-existent local programs and a lack of economic incentives. And there has been no statewide inventory to identify buildings at greatest risk. Newly introduced legislation,
Assembly Bill 429, could fix  that.

Moreover, local roads, utility distribution lines and many homes have yet to see upgrades. And there are deep concerns about telecommunications. AT&T and Verizon, two of the Bay Area’s largest cellphone providers, say their systems seismically are up to date but haven’t revealed how these lifelines would be affected in a worst-case quake scenario.

Meanwhile, our population has surged from 6 million in 1989 to 7 million, with one of the world’s highest concentrations of wealth and innovation.

And the next earthquake to challenge our cities may not rupture in the remote Santa Cruz Mountains, like the 1989 temblor.

It may be underneath our feet.

Monday night’s 4.5-magnitude earthquake that jolted Concord and Pleasant Hill in the East Bay could be felt from Vallejo to Santa Cruz. It was centered west of the Concord fault and north of the Calaveras fault. Tuesday afternoon’s 4.7-magnitude earthquake, rattling San Jose and the South Bay, erupted near Hollister along the San Andreas fault.

But each new major earthquake inspires innovations in structural engineering,

“As we study each earthquake and prepare, we change how we retrofit and build new construction,” said Jeff Brinks, vice president of DCI Structural Engineers, which works with Swenson Builders around the Bay Area.

San Francisco’s slender One Rincon Hill South Tower — 60 stories tall — has a technology called “tuned liquid sloshing dampers,” which reduce the vibration that can lead to structural failure, as well as reinforced concrete shear-wall at its core and special bracing, said U.S. Geological Survey earthquake engineer Mehmet Celebi.

Dampers also were installed in the 13-story Santa Clara County Government Center in downtown San Jose.

During the Loma Prieta earthquake, “that building had a serious problem,” Celebi said. “It was vibrating like a crazy dog.”

Kaiser Redwood City’s new hospital is equipped with “buckling restrained braces,” designed with a slender steel core, a concrete casing and a layer of material that decouples the two — absorbing the energy from an earthquake, he said.

In addition to bracing and shear walls, Oakland’s historic City Hall, which was uninhabitable after the quake, was retrofitted with a state of the art seismic base isolation system, hidden it its basement. The building sits on several huge shock absorber bearings built between the building and the ground, allowing the structure to slide back and forth but remain upright.

The new Apple building uses the same technology, mounted on 700 base isolators that let the building — with six miles of precious glass — move as much as 54 inches in any direction during a quake, said structural engineer Jawed Umerani, Palo Alto’s Umerani Associates, Inc., part of the design team behind the Apple campus.

“The building can slide and not hit anything,” said Umerani.

At the new Stanford Hospital, an estimated 10,000 braces hold utility pipes and ductwork, according to Bert Hurlbut, vice president of new hospital construction at Stanford Health Care. The hospital’s atrium — made of about 11,000 square feet of glass panels — relies on caulking to deform during an earthquake, with a film of plastic to protect against falling shards.

While new construction is designed to flex and bend, older retrofits must stiffen, strengthen and often preserve historic elements, said Ron Coté, senior vice president of Swenson Builders, which retrofitted the dangerous unreinforced masonry of San Jose’s St. James Hotel, Hayes Mansion, Security Building, Letitia Building, Knox-Goodrich Building and others.

The challenge faced by the small city of Santa Cruz was how to protect both its past and its future. It lost a total of 31 buildings. And many of its surviving structures needed better protection.

At stake was its survival — and its soul.

The iconic Pacific Garden Mall, a leafy street that snaked through the heart of downtown, was ruined. A bit threadbare, with little nightlife and a quiet retail and restaurant scene, this was the heart of blissful counterculture. In the sleepy evenings, “Rainbow Ginger” Johnson played the tambourine and twirled in front of the old Cooper House, as soft music played.

“It was beautiful. It represented a whole culture in an era of peace and love, with an ethos that you should be friends with everybody,” recalled Gibson. “And once that had been uprooted, very literally, it left behind holes in our heart.”

Now there’s a different downtown. It’s commercial and bustling. Seedy bars and bong shops have been replaced by pricey retail shops, housing, movie theaters, an Art and History museum, an organic ice cream store and restaurant crowds that spill into the street. There’s twice as much development, with a million square feet of new construction replacing the half-million square feet of destroyed residential or commercial  buildings.

Only one dangerous unreinforced masonry building remains — and it’s vacant, said Santa Cruz Deputy Building Official John McLucas. The rest of the old “soft story” storefronts now have large footings with resilient frames, better bolting, braced roof parapets and injected epoxy into the grout joints of the brick walls.

The new Park Pacific project — a five-story, 6,000-square-foot project fronting Pacific Avenue and Cedar Street — is emblematic of the change. The site of the quaint Bookshop Santa Cruz and Santa Cruz Coffee Roasting Company will house a restaurant, parking garage and 79 modern condominiums, engineered to meet tough new standards.

“The earthquake was a chance to look farther ahead into the future,” said Tom Brezsny, a 40-year resident of Santa Cruz and realtor with Sereno Group Real Estate. “It was a blank slate. All bets were off.”

“Santa Cruz had no choice,” he said, “but to reinvent itself.”

According to a 2018 U.S. Geological Survey report, the total investments in each county for seismic retrofitting or replacement since the Loma Prieta earthquake are:
• San Francisco (city and) County: $31 billion; includes retrofits of the Golden Gate
Bridge and all water supply seismic improvements.
• Santa Clara County; $12 billion; includes $4.3 billion for San Jose and $3.5 billion for
Palo Alto.
• Alameda County: $11 billion; includes $5.2 billion for Oakland and $3.2 billion for
Berkeley.
• San Francisco-Oakland Bay Bridge retrofit and replacement: $10 billion.
• San Francisco Bay Area-wide retrofits: $6 billion; includes Pacific Gas and Electric
Company upgrades throughout the Bay Area, Bay Area Rapid Transit system
upgrades, retrofits of Caltrans elevated freeways, and the California Earthquake Brace +
Bolt program for single family homes.
• Contra Costa County: $6 billion; includes $1.4 billion for the Antioch Bridge, Benicia
Bridge, Carquinez Bridge and Richmond-San Rafael Bridge retrofits and replacements.
• San Mateo County: $4 billion; includes $0.3 billion for the Dumbarton Bridge and the
San Mateo-Hayward Bridge retrofits.
The largest investments have occurred in the retrofit and replacement of transportation infrastructure, primarily state toll bridges, by Caltrans and BART ($20 billion); the retrofit and replacement of acute care facilities as mandated by California Senate Bill 1953 ($19 billion); the upgrade of unreinforced masonry, soft-story, and other privately-owned buildings ($10 billion); the retrofit and replacement of public and private schools ($8 to 12 billion); and the seismic strengthening of water supply and sewer systems ($7 to 10 billion).

https://www.mercurynews.com/2019/10/16/loma-prieta-30-years-later-santa-cruz-rises-from-the-rubble-to-become-a-model-of-earthquake-preparedness/

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