When an earthquake collapsed two 50-foot sections of the San Francisco-Oakland Bay Bridge during the 1989 World Series, the nightmares of hundreds of thousands of commuters who cross the Depression-era span each day were brought to life.

On this 20-year anniversary of the 6.9-magnitude earthquake that killed 63 people, injured almost 3,800 and caused up to $10 billion damage, the bridge reconstruction has become the largest public works project in California history and is still years from completion.

Although thousands of buildings, highway bridges and landmarks such as San Francisco City Hall have been fortified, other earthquake safety problems are far from fully addressed in this region where experts say another major temblor is certain to strike.

Some schools that the state says are at risk of collapse still have not been repaired. And vulnerable apartment buildings that house hundreds of thousands of people have not been seismically retrofitted by their owners.

Millions were tuned in on television to watch Game 3 of the "Bay Bridge World Series" between the San Francisco Giants and the Oakland Athletics when the shaking began. The broadcast went dark, with the vast audience riveted to their TVs, and then sportscaster Al Michaels' audio returned with reports that a strong earthquake had struck.

"The Loma Prieta earthquake is always referred to as a wakeup call and we're fortunate over the last 20 years that we've had no other major earthquakes," said Jack Boatwright, a seismologist with the U.S. Geological Survey. "Much work has been done but we cannot rest in these efforts."

It took only four years during the Great Depression to build the Golden Gate and Bay bridges, but the reconstruction of the eastern span of the Bay Bridge has been plagued by costly delays and political gridlock over its unconventional design. Originally the cost was put at $1.3 billion with a 2004 completion; that has ballooned to $7.2 billion with a 2013 opening.

"What this region and the state is trying to do here is unique," said Bart Ney, a spokesman for the California Department of Transportation, who is managing the project. "We're trying to build a world class structure, an architectural icon and a seismic innovation all at one time in one of the most seismically challenged areas of the world. Because of the complexity of all of that, it's taken us a long time to do it."

Some bridge experts, however, say the decision to rebuild rather than strengthen the existing bridge was a pricey mistake.

A team of 40 researchers sponsored by the National Science Foundation (NSF) and Caltrans to study the Oct. 17, 1989 earthquake's effects on the bridge recommended in 1992 that the current bridge be retrofitted, not replaced, for an estimated cost of $230 million.

But a 1996 study by Caltrans' Seismic Advisory Board disagreed with these findings, saying the cost of replacing the bridge was comparable with retrofitting it.

The new span wound up costing billions of dollars and is less quake resistant than the existing bridge, said Abolhassan Astaneh-Asl, a civil engineering professor at the University of California, Berkeley.

"You are going to get a bridge, in my opinion, that is less safe than the existing east span. The bridge didn't need to be replaced," said Astaneh-Asl, who was the lead investigator in the NSF and Caltrans five-year study of the seismic performance of the bridge's east span, and who submitted an alternative design after officials chose to replace it. "This replacement is worse than what we have."

The signature part of the new eastern span is a single-tower, self-anchored suspension bridge larger than any other in the world. It uses leverage to support the roadway by using a cable looped over the tower and anchored into the ends of the roadway itself. On traditional suspension bridges, like the Golden Gate, the main cables are connected to huge concrete blocks embedded in the ground at each end of the span.

If one section of the new self-anchored bridge fails in an earthquake, Astaneh-Asl said, the entire structure could fail.

But Caltrans' Ney said the new bridge is the safest of the designs that were aesthetically pleasing to local leaders and others who had a say in the final choice.

"We originally pitched a concrete viaduct bridge, which we know how to build well, and the community, leaders and the media criticized it as a vanilla design," Ney said. "If the community doesn't want it, we have to listen."

While cost and delays have been troubling, Ney said there is no question the right decision was made. "The bridge is 70 years old," he said. "It's reaching the end of its life span."

Meantime, another large earthquake is destined to occur — scientists in 2008 said there is a 63 percent probability of a comparable quake in the Bay area over the next 30 years. And the Bay Bridge is not the only complicated public safety project to move slowly.

In 2003, years after a newspaper investigation exposed thousands of vulnerable public school buildings in California, a state audit determined California schools could need at least $5 billion in seismic work.

But in many districts, expensive retrofitting projects are not feasible in these challenging economic times.

In 2006, a voter-approved measure set aside $200 million to help districts with seismic projects, but only five school districts have applied. To date, only one grant has been awarded, $3.6 million to San Ramon Valley High School in Contra Costa County to retrofit its gymnasium.

State officials who compiled a list of the 25 almost quake-vulnerable school buildings are baffled about why more districts have not sought money, which can be used to determine seismic risk or do repairs.

"We can't really speak to why schools have not applied," Eric Lamoureux, spokesman for the Department of General Services, said. "We have done significant outreach to districts about the availability of the funds."

At Oakland Technical High School the school auditorium and girls' gymnasium have been identified by the state as older building types in danger of collapse or damage during a major earthquake.

Oakland said the grant would not cover all the repair costs, leaving the cash-strapped district on the hook to complete the project.

"If you include finishing and structural work, the grant would cover only 50 percent of our costs," Troy Flint, a spokesman for Oakland Unified School District said.

Many of the structures that collapsed during Loma Prieta and Southern California's Northridge earthquake in 1994 were so-called "soft-story" buildings — those built with garage or commercial space on the first floor providing little support in a strong temblor.

While unreinforced masonry buildings have been retrofitted in San Francisco, a recent Association of Bay Area Governments (ABAG) study found that thousands of Bay Area residents are still living in soft-story dwellings that have not been retrofitted.

"The problem is that the economy stinks, so some of these programs people thought about making mandatory ... it's just terrible timing," said Jeanne Perkins, earthquake preparedness manager for ABAG.

Only one city in the Bay area, Fremont, has passed mandatory retrofitting for these unsafe buildings, according to the ABAG study.

Berkeley has a law mandating that owners get an evaluation and a plan to fix their buildings, but does not require that the work actually be done.

In Oakland, 26,000 of the city's 163,000 units would become uninhabitable in a 7-magnitude earthquake on the Hayward fault, ABAG's research found. Oakland has mandated an audit of its soft-story buildings.

San Francisco has the largest number of soft-story apartments, at least 12,400 multiunit buildings with tens of thousands of units, according to the ABAG study. So far, the city has been unable to find a way to mandate owners to strengthen their properties, but Mayor Gavin Newsom directed the city's Department of Building Inspection to write an ordinance making upgrades to these unsafe buildings mandatory.

"It's in process," said the mayor's spokesman Nathan Ballard. "We are convening a task force, working with building owners to ensure it's done right."