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Seismic study finds Metro Vancouver buildings could shake more than predicted if 'Big One' hits

Last Updated Nov 30, 2020 at 5:02 pm PDT

FILE - Vancouver. (Riley Phillips, NEWS 1130 Photo)

New UBC report finds the ground where some tall Metro Vancouver buildings stand too soft in event of an earthquake

The lead researcher says the ground would jiggle more during an earthquake than previously thought

Older buildings can be a problem since codes were different when they were constructed

VANCOUVER (NEWS 1130) — If “the big one” was to hit Metro Vancouver, many tall buildings would experience way more shaking than previously predicted because the ground they’re built on is too soft, according to a new seismic study from UBC.

The study’s lead researcher, Carlos Molina Hutt, says that doesn’t mean the buildings will crumble, but previous models are underestimating the impact of a magnitude 9 earthquake.

“The Metro Vancouver region lies above the Georgia sedimentary basin which is made up layers of glacial and river sentiment that sit on top of sedimentary rock, and in the event of an earthquake, these layers will jiggle and amplify seismic waves causing more intense and long-lasting tremors than outside the basin,” he explains. “If you’re inside the basin you’re going to experience shaking that’s more severe than if you were outside the basin on firmer ground.”

The amplificant of shaking caused by the basin wasn’t taken into account in the 2015 seismic hazard model, according to the study.

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Molina Hutt adds there are complications when it comes to older tall buildings because they were constructed under dated building codes. Those built in and before the 1980s are most at risk of severe damage or even collapse. Buildings in the range of 10 to 20 storey-range risk the worst impacts, the study found.

“When we build a structure, it only needs to meet the code of the time when it was built. If there is a future change in the code, you don’t have to go back and upgrade your building. To address vulnerable existing buildings, jurisdictions must explore different seismic risk reduction policy options and adopt the most effective mitigation strategies,” Molina Hutt says.

He says he wants provincial and national guidelines updated to keep the soft ground in mind for future construction.

Molina Hutt notes the impacts in the study are preliminary and capture relative risk, and there are still many uncertain variables.