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High-rises at risk: Building codes underestimate Vancouver’s seismic hazard

State of the art simulations reveal that Vancouver’s tall concrete buildings are especially vulnerable to some types of seismic waves.

If you’ve lived through a serious earthquake and the building you were in emerged relatively unscathed, you may have local building codes to thank. Building codes are construction standards that are guided by science and set by the government to uphold public health, safety and welfare. In an earthquake-prone region, these guidelines often require foundational supports beneath the soil or limit the allowed types of building materials, both of which determine the ability of the building to withstand a specified level of shaking.

Building codes are regularly revised as scientists develop new ground motion models to more accurately describe how future earthquakes might affect a region. In Metro Vancouver — Canada’s third largest metropolitan area and the region with the country’s highest seismic risk — the existing models used to develop present-day building codes have underestimated the region’s seismic hazard, according to a new study led by researchers from the University of British Columbia.

Metro Vancouver lies near the Cascadia Subduction Zone, an active tectonic plate boundary stretching 620 miles (1,000 kilometers) from Northern California to northern Vancouver Island. Should the fault act up, the impact would be exacerbated by the fact that Metro Vancouver sits on the Georgia sedimentary basin. Here, the deep sedimentary deposits of the basin are softer and less compact than the surrounding bedrock. This type of rock will amplify shaking caused by seismic waves.

“We’re surrounded by mountains, and we have most of our buildings and infrastructure in this sedimentary basin,” says Carlos Molina Hutt, referring to Metro Vancouver. Molina Hutt is a professor of structural and earthquake engineering at the University of British Columbia and an author of the study. He and his co-authors looked at how the Georgia sedimentary basin — a factor not explicitly considered in the current building code, he says — could affect shaking in the event of a large earthquake in the Cascadia subduction zone.

Simulating shaking in Metro Vancouver

Ground motion models, which serve as the foundation for Canada’s national seismic hazard model, typically rely on past observations of earthquakes from all around the world. The data are then extrapolated to other parts of the globe such as Metro Vancouver. But this area has unique geological features not captured by these models, such as its soft sedimentary basin. Additionally, the last large-magnitude Cascadia subduction zone earthquake here occurred more than 300 years ago, so there are few records of past earthquakes that ground motion models can consult.

To improve these models, Molina Hutt and his colleagues instead relied on a different technique altogether: observations of shaking from a simulated earthquake in the Cascadia Subduction Zone, dubbed the “M9 scenario.” Researchers from the U.S. Geological Survey (USGS) and the University of Washington, Seattle developed the M9 simulation by creating a detailed 3D computer model of the Cascadia landscape, within which they triggered an artificial magnitude-9.0 earthquake. The researchers generated 30 possible earthquake scenarios, varying parameters such as the earthquake location and the direction of the rupture — toss-up parameters in future earthquakes. Molina Hutt and his co-authors used these M9 simulations to determine how much the sedimentary basin could amplify shaking and what effect this shaking could have on buildings.

The M9 simulations work better than traditional ground motion models because they’re more detailed and location-specific, says Molina Hutt. The team’s calculations show that the M9 simulations highlight what traditional ground models had missed: The soft Georgia basin amplifies long period earthquake waves.

After extracting the relevant earthquake details from the M9 scenarios, Molina Hutt and his colleagues simulated how concrete shear wall structures — the most common type of high-rise in Metro Vancouver — would fare during an earthquake. They found that high-rise buildings like those found in Metro Vancouver are more vulnerable than their shorter neighbors. Just like how a longer pendulum traces out wider arcs in space, taller buildings will sway farther in an earthquake, with longer time intervals for each sway. This long period sway matches long period ground shaking that the researchers found to be amplified in the basin. That’s bad news, because similar periods of shaking translate to more efficient transfer of destructive energy from ground to building. The team found that older buildings adhering to Canada’s building codes predating 1990 are at higher risk of severe damage or even collapse than modern buildings.

Older buildings are at risk

“Some of these tall buildings that were constructed before 1990 are not going to fare too well [in an earthquake],” says Molina Hutt. “Obviously, there’s a lot of work that’s needed to better quantify the impact [of earthquakes] on these buildings and see what we can do to enhance their performance.”

The study is important for guiding new policy, says Tiegan Hobbs, a research scientist for the Geological Survey of Canada who was not involved in the study. She says the Vancouver area has many tall concrete buildings from the 60s and 70s. Molina Hutt and his co-authors were able to “use the most state-of-the-art research to figure out exactly how much of a problem [these buildings are].”

“To have studies that look at the seismic risk from a really rigorous engineering approach, like the simulations [this team] was doing on these concrete building typologies is a great contribution,” says Hobbs.

Old buildings erected under outdated building codes aren’t required by law to be retrofitted to comply with the most recent codes. To enact such a policy would be costly and complicated. Molina Hutt says he doesn’t recommend a sweeping mandate just yet. For now, researchers are still trying to accurately determine the seismic risk to different types of buildings in the area. “What we want to do is raise awareness,” says Molina Hutt. He hopes this work can push the government “to explore whether there’s a need for mandated assessment of certain types of buildings or a mandated retrofit.” He says, “Our work is helping to shape that discussion and inform that conversation.”

Source: https://temblor.net/earthquake-insights/high-rises-at-risk-building-codes-underestimate-vancouvers-seismic-hazard-12522/

National seismic model underestimates shaking in buildings from magnitude 9.0 earthquake: UBC study

A team of scientists at UBC say tall buildings across the Metro Vancouver region will shake much more than currently predicted by Canada’s national seismic hazard model if and when a magnitude 9.0 earthquake, like “The Big One,” hits.

Metro Vancouver sits upon the Georgia sedimentary basin. And the researchers say the hazard model doesn’t account for how that basin would amplify seismic waves.

“As a result, we’re underestimating the seismic hazard of a magnitude 9.0 earthquake in Metro Vancouver, particularly at long periods,” said lead researcher Carlos Molina Hutt, in a statement Monday about the study.

“This means we’re under-predicting the shaking that our tall buildings will experience.”

The Georgia basin consists of layers of glacial and river sediment on top of sedimentary rock.

Molina Hutt says it is the difference in the properties between the softer sedimentary rock and the surrounding bedrock that results in the amplification of the shaking.

Based on their computer simulations, the researchers found that the amplification is greater in areas where the Georgia Basin is deeper.

Richmond and Delta would experience the most amplification, he says, followed by Surrey, New Westminster, Burnaby, Vancouver and North Vancouver. Areas just outside of the basin, like West Vancouver, will experience the least.

Molina Hutt says older, taller buildings are the most at risk.

The research looked at concrete shear wall buildings. Molina Hutt says those built with building codes from the 1980s and earlier, risk sustaining severe damage or even collapse during a magnitude 9.0 earthquake. Buildings in the 10- to 20-storey range would sustain the worst impacts.

There are more than 3,000 concrete shear wall buildings in the Lower Mainland. A shear wall building is constructed to resist lateral movement to its plane, like wind and seismic activity.

“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,” said Molina Hutt, who is a structural and earthquake engineering professor at UBC.

He says jurisdictions should take active steps to understand the seismic risks in their building stock and develop risk reduction strategies.

Canada’s latest national seismic hazard model was released in October. And while the greater risk is currently unaccounted for, Molina Hutt says Natural Resources Canada, which is responsible for the hazard model, is aware of the potential effects of the Georgia Basin and is actively researching it.

Source: https://www.cbc.ca/news/canada/british-columbia/national-seismic-model-underestimates-shaking-in-buildings-from-magnitude-9-0-earthquake-ubc-study-1.5822881

Seismologists record more than 3,500 ‘tiny tremors’ on Vancouver Island in nine days

Natural Resources Canada seismologist John Cassidy, otherwise known as Earthquake Guy, says these are not earthquakes but rather a good reminder that we live in an active subduction zone.

Seismologists have recorded more than 3,500 tiny tremors on Vancouver Island, but don’t panic, these aren’t earthquakes. That’s the last thing B.C. needs in 2020.

Natural Resources Canada seismologist John Cassidy, otherwise known online as the Earthquake Guy, posted a tweet early Thursday about the event. He says while these tremors don’t provide answers to when a major earthquake will hit, they “certainly remind us that we live in an active subduction zone.”

The cluster of tiny tremors is likely an ETS event, an episodic tremor and slip, said Cassidy. ETS is a process that occurs deep below the Earth’s surface along faults that form the boundaries of tectonic plates. It involves repeated episodes of slow fault slip of a few centimetres over a period of several weeks, accompanied by seismic tremors.

ETS events can help scientists better understand the quake hazard by studying how it affects the subduction fault beneath the Island, which is about 30 kilometres beneath the surface, and in Vancouver, at 60-to-70 km beneath the surface.

“This is helping us to map out where the subduction fault is completely locked and storing energy,” he said. “These look very different from earthquakes but we can get a better understanding of the process … There are still a lot of questions.”

During ETS events there is also a “slip,” where the region moves to the west over the course of a few weeks.

“This is quite remarkable when you think about Vancouver Island moving a few millimetres,” he said. “But it’s not clear whether this will impact that subduction fault.”

ETS events are a regular occurrence on the Island, and happen about every 14-to-15 months. The last ETS event on southern Vancouver Island was one year ago, said Cassidy.

“These tiny tremors that we locate … have a very different appearance on our seismographs (than quakes). Energy builds up slowly and drops off slowly. They are not felt but can be detected and located by our very sensitive seismographs,” he said. “It’s the slip that we are really watching for.”

The Cascadia Subduction Zone, which runs from northern Vancouver Island to Northern California, is Canada’s most active earthquake region.

As for a major quake, Cassidy says scientists still can’t say when this will happen or how large the next one will be, but huge strides have been made in understanding temblors and how often they strike an area. Unlike 20 years ago, seismologists now know that B.C. has seen magnitude-nine earthquakes and that they occur roughly every 500 years or sometimes as short as 200 years between quakes.

“We know the last one struck on Jan. 26 of the year 1700. So we know the exact date and time,” said Cassidy.

Source: https://vancouversun.com/news/seismologists-record-more-than-3500-tiny-tremors-on-vancouver-island-in-nine-days

New study detects thousands of earthquakes in B.C. Peace region, most linked to fracking

B.C.’s Peace region is experiencing roughly 1,500 small earthquakes a year and most of them are connected to fracking operations, according to a new study.

Researchers set up 15 earthquake detectors around the region and recorded 5,757 tiny earthquakes that were otherwise undetected between 2017 and 2019.

“The vast majority of them seem to be connected with hydraulic fracking operations,” said Alessandro Verdecchia, one of the study’s lead researchers, during an interview on CBC’s Daybreak North. The research was published in the Seismological Research Letters journal in July.

According to the McGill University geophysicist, the connection was made by pinpointing the precise time and location of seismic events and comparing that data to information from fracking companies about their operations.

“If we see some kind of connection in time and place between the operation and the occurrence of the earthquake we can associate an occurrence of the earthquake with the fracking operation.”

Detecting large magnitude quakes

Verdecchia says the researchers are trying to determine the largest magnitude earthquake that can be created by fracking in the western Canada sedimentary basin, a region in northeast British Columbia that includes the Montney Formation, a shale gas area that’s home to nearly 3,000 production wells.

“Large magnitude events can produce larger acceleration and velocity of the ground and, of course, can produce larger damages to infrastructure,” he said.

In 2018, a 4.5 magnitude earthquake shook Fort St. John. No damage was reported, but people could feel it as far as Dawson Creek and Chetwynd.

Verdecchia says the largest magnitude detected in the western Canada sedimentary basin that’s been associated with fracking was a 4.6 event in August 2015. However, in China, there has been a magnitude 5.5 seismic event that’s been connected with a hydraulic fracking operation.

The other thing researchers want to understand is how far from the fracking these events can occur.

“This will be helpful for operators when they decide to start a fracking well, to begin operations, because they can more or less keep a distance let’s say from important infrastructures or populated areas,” Verdecchia explained.

According to the research so far, seismic events have been detected at a distance as far as five kilometres from the fracking operations.

Source: https://www.cbc.ca/news/canada/british-columbia/new-study-detects-thousands-of-earthquakes-in-b-c-peace-region-most-linked-to-fracking-1.5668236

4.5-magnitude earthquake strikes off Vancouver Island, reported felt in Vancouver

An earthquake that struck off the coast of southern Vancouver Island Friday afternoon was reportedly felt in downtown Vancouver.

Earthquakes Canada said the 4.5-magnitude quake struck 36 kilometres southwest of Bamfield just after 1:30 p.m.

The United States Geological Survey (USGS) initially recorded the quake at a 4.8 magnitude, but later lowered it to a 4.5.

Both agencies said no tsunami is expected, and no reports of damage have been received.

Nearly 300 people have reported feeling shaking to the USGS. Another 200 people on Vancouver Island also reported feeling the quake, with most putting it at a Level 2 intensity.

However, some people in downtown Vancouver said they felt shaking, including workers in Robson Square and on Main Street.

Residents of other parts of Metro Vancouver, including Richmond and Burnaby, also said they felt slight shaking.

Friday’s quake comes days after a 4.8-magnitude earthquake struck further north off the island coast. Nine others struck in the same area west of Port Hardy around Christmas Day.

Source: https://globalnews.ca/news/6459690/earthquake-vancouver-island-felt/

4.7 magnitude earthquake rattles Haida Gwaii

An earthquake rattled the west coast of Haida Gwaii in British Columbia on Saturday.

Earthquakes Canada says the quake with a magnitude of 4.7 struck about 50 kilometres south of the Village of Queen Charlotte.  The national earthquake agency says the tremor occurred just before 11 a.m.

Earthquakes of that magnitude are often felt but typically only cause minor damage, if any.

There were no immediate reports of damage or a tsunami risk.

There have been a number of small earthquakes in Haida Gwaii over the past month but none were higher than a magnitude 2.8.

Source: https://www.cbc.ca/news/canada/british-columbia/haida-gwaii-string-of-earthquakes-1.5354680

Map shows which areas of Vancouver face most damage in an earthquake

Chinatown, Kitsilano, South Granville and West End would be hardest hit, map shows.

A map released by the City of Vancouver highlights areas that would see the most severe damage during a significant earthquake.

The map was produced as part of the city’s ongoing investments to assess earthquake risk and upgrade infrastructure.

It shows a magnitude 7.3 earthquake would cause the most damage to Vancouver’s older, multi-family residential and commercial areas.

Chinatown, Kitsilano, South Granville and the West End would be hit the hardest, with pockets of damage also highlighted in the Point Grey, Strathcona, Mount Pleasant and Marpole areas.

The map also shows that much of the southern half of Vancouver would see limited damage, although a statement from the city said disruption from such a powerful shake would be felt city-wide.

City officials released the map in preparation for the 2019 Great British Columbia ShakeOut drill, held Thursday morning.

“During an earthquake, the best thing you can do is drop, cover, and hold on,” read a city statement.

The drill is designed to encourage all British Columbians to practise their response to an earthquake and assess emergency preparedness.

Strong earthquake hits near volcanic Alaskan islands

A strong earthquake shook volcanic islands between Alaska and Russia yesterday in the northern part of the Pacific Ring of Fire.

A 6.5-magnitude earthquake occurred at 12:35 p.m. local time (1:35 p.m. B.C. time) on April 2, according to the U.S. Geological Survey.

The epicenter was located in the Rat Island of the Aleutian Islands at a depth of 19 kilometres (12 miles) and 93 kilometres (58 miles) northwest of Amchitka, Alaska.

A tsunami was not expected from the quake, according to the U.S. Tsunami Warning System.

Source: https://www.straight.com/news/1222971/strong-earthquake-hits-near-volcanic-alaskan-islands

2.2 magnitude earthquake ‘lightly felt’ in Salmon Arm

A 2.2 magnitude earthquake was felt by some residents of Salmon Arm, B.C. on Saturday night.

According to Earthquakes Canada, the quake was “lightly felt” around 8:40 p.m. There were no reports of damage.

Many residents said they felt their houses shake, and heard something that sounded like an explosion.

Source: https://www.cbc.ca/news/canada/british-columbia/earthquake-salmon-arm-1.5040985

Fracking connection probed in 4.6-magnitude earthquake near Sylvan Lake

The Alberta Energy Regulator is working to determine if a fracking operation caused an earthquake near Sylvan Lake and Red Deer on Monday.

Natural Resources Canada said a 4.6-magnitude earthquake rocked parts of central Alberta just before 6 a.m. The federal department’s website said the tremor was classified as a light earthquake.

The AER has confirmed Vesta Energy had been fracking in the area just prior to the quake, which was detected by the company’s private seismic monitoring devices around 12 kilometres south of Sylvan Lake at a magnitude of 4.16.

The AER said the earthquake was reported to them by the company at 6:20 a.m.

“We are currently reviewing the events to determine if the incident is due to hydraulic fracturing activities or natural causes,” said Natalie Brodych, spokeswoman with the AER.

The regulator said Vesta has stopped work at the site while the AER investigates whether fracking led to the quake.

Earthquakes Canada initially had trouble pinpointing the earthquake, locating it first northeast of Red Deer, then south of the city. The most recent update has placed it 19 kilometres west of Red Deer, near Sylvan Lake. The earthquake occurred about a kilometre below the surface.

There were no immediate reports of damage, but power was knocked out for about 4,600 FortisAlberta customers. A spokesperson said the disruption lasted for a little more than an hour.

AltaLink said a transformer at a substation south of Sylvan Lake tripped around the same time of the quake. The transmission company is still investigating exactly what caused the outage.

The U.S. Geological Survey website says an earthquake similar to the one that struck Alberta has a sensation like a heavy truck striking a building; it can rattle windows and may break some dishes or windows.

Debbi McGillicky, who lives in the Mountain View area of Red Deer, said she and her husband were jarred awake by the quake.

“My husband and I were awakened at 5:55 a.m. when our bed began to shake violently. My husband shot up out of bed and exclaimed, ‘What the hell was that?’,” she told Postmedia. At the time, she thought the quake was some sort of explosion.

Linda Borsato lives in Sylvan Lake and said she was eating breakfast when the earthquake hit.

“There was a pop and the power went out, and right after the power went out the whole house shook from one end to the other,” she said.

“It was pretty freaky to say the least. We didn’t really know what to do when it first happened. . . It was enormous.”

Earthquakes are rare for the Red Deer area; the last recorded quake was in 2016. There was a 4.0-magnitude quake on March 31, 1997.

However, Joanne Gaudet, communications officer for the town of Sylvan Lake, said there has been seismic activity in the past between Sylvan Lake and Rocky Mountain House to the west.

Source: https://calgaryherald.com/news/local-news/red-deer-hit-with-earthquake-monday-morning