The B.C. government has been working to strengthen, upgrade and retrofit some of Vancouver's major bridges, overpasses and tunnels to withstand an earthquake of magnitude 6 or 7.

But in the Metro Vancouver area, a major bridge and a busy tunnel — the Pattullo and the George Massey — would still pose an elevated risk in the event of a major earthquake, according to provincial standards.

Kevin Baskin, chief bridge engineer for the B.C. Ministry of Transportation, said that since the mid-1990s, the province has spent about $100 million on a highway infrastructure seismic retrofit program, prioritizing "lifeline" structure and disaster response routes.

The Lions Gate Bridge, the Oak Street Bridge, the Queensborough Bridge and the Pitt River Bridge are some of the "lifeline" priorities the government identified and upgraded. Bridges built within the last 25 years don't need the same retrofits as older structures.

"Since the mid-1980s, bridge design codes have had specific requirements in them for seismic design," Baskin said.

Structures built or upgraded since then are going to meet modern seismic standards, he said, but some older structures still pose a particular risk.

End-of-life bridge

The 74-year-old Pattullo Bridge, which links North Surrey with New Westminster, has received no seismic upgrades at all from its previous owner, the province, or from Translink, its owner and operator for the past 12 years.

Ken Hardie, a spokesman for Translink, said there is no point performing seismic upgrades on the 76-year-old Pattullo Bridge, which is operated by Translink.

"In the event of a major incident, I think it would be safe to say the Pattullo would be closed, and perhaps for an extended period," Hardie said.

"It's a very old bridge," he said.

Translink is nearing a decision on whether to retrofit the bridge or replace it, he said.

"On balance, Translink's preference is to build a new bridge because then you're looking after capacity issues and seismic upgrades," Hardie said. "Will we be spending hundreds of millions of dollars in seismic upgrades? Probably not."

John Clague, a geologist and seismologist at Simon Fraser University, is an earthquake hazard expert who says the decision on the potentially problematic bridge can't be put off any longer.

"I think we desperately need to look at that particular bridge to see whether it can withstand strong shaking," Clague said. "It's an important piece of our infrastructure."

Liquefaction danger

The 53-year-old George Massey Tunnel, in the Fraser River between Delta and Richmond, is another vital link in the Lower Mainland that could be in danger during a quake, Clague said.

Baskin said the Massey tunnel, which is owned by B.C. and maintained by a contractor, has been retrofitted to withstand what engineers call a "one in 475-year" earthquake event.

"The work that's been done on the Massey tunnel is the structural seismic retrofit," Baskin said. "The components of the structure have been tied together so that during shaking, it reduces the risk of structural damage."

But Clague is concerned about the tunnel, which sits on the silty and sandy river bottom in the Fraser.

During an earthquake, a process called liquefaction could cause partial sinking of any or all of the six tunnel segments.

"Loss of life is a potential issue," Clague said.