Old buildings, coastal areas most vulnerable to major earthquake in B.C.

Old buildings, coastal areas most vulnerable to major earthquake in B.C.

Older structures and low-lying coastal areas would be most at risk if a powerful earthquake were to strike southwestern B.C., according to seismologist John Cassidy of Natural Resources Canada.

“You would see the greatest effects along the west coast of Vancouver Island,” said Cassidy—both the strongest shaking and the highest tsunami waves. “In Victoria and Vancouver, you would see damage mainly to older buildings—brick buildings, for example, that haven’t been retrofit.”

Newer, earthquake-resistant buildings would be less likely to collapse, although falling glass would be a likely hazard in inner-city areas.

To estimate the impacts of a massive quake, Cassidy and his colleagues use a set of models based on evidence from past seismic events in northwestern North America, and the effects of recent disasters of similar magnitude that have occurred elsewhere—including northern Japan, Chile, and Sumatra, Indonesia.

The models suggest that shaking would last three to five minutes, and would be followed by a tsunami—which, like the seismic waves, would diminish in intensity the further it travelled from its point of origin, Cassidy explained.

“The wave essentially loses energy as it propagates through the Strait of Juan de Fuca, around the Salish Sea and into Vancouver.”

The wave would be three to four metres high in Victoria Harbour, and roughly half that height in Vancouver, the models project.

Southwestern B.C. lies near the edge of a subduction zone, where the the Juan de Fuca tectonic plate is being submerged beneath the larger North American plate. Over time, stress and compression build within the rocky crust, until the energy is suddenly released—causing the land to shudder. Geological records and Indigenous oral histories indicate that subduction earthquakes near 9.0 on the Richter scale occur in our region at intervals of between 250 and 850 years. The most recent of these cataclysms struck just over three centuries ago.

“We have this ocean plate that’s being pushed toward us at about four to five centimetres a year,” roughly the pace at which our fingernails grow, said Cassidy. “But over 100 years—over a lifetime—that represents four to five metres of movement.”

Three different types of earthquakes affect southwestern B.C., said Cassidy: the megathrust subduction earthquake discussed above; the crustal earthquake; and the deep earthquake. The latter two tend to be less intense, but are more frequent. Events like the 7.8-magnitude tremors near Haida Gwaii in late October 2012, that sparked a tsunami warning, can also pose substantial dangers.

Various levels of government have acknowledged these risks. Canada’s National Building Code requires that structures conform to a high standard of earthquake resistance, and seismologists at Natural Resources Canada have created maps of communities based on seismic dangers. The provinces each have emergency response plans, and the federal government’s Department of Aboriginal Affairs has a protocol for emergency response on First Nation reserves. The City of Vancouver, like many other municipalities, has recently updated its earthquake preparedness plan.

Emergency planning specialist Gordon Redmond believes that, while those measures are all laudable, officials and civilians alike would be better served by a more comprehensive approach to risk mitigation and response—both in terms of public safety and financial cost.

“It’s great to see that [governments] are taking these threats seriously, and that they’re looking at programs and strategies to address them,” said Redmond. However, “it would be more cost-effective if they would look at a basket of hazards” and consolidate them into a single risk assessment, he added. The price tag of natural disasters in B.C.—including fires, floods, landslides and wind storms—is rising, and according to Redmond’s calculations, cost an average of $184,000 per day from 2007-2012.

“If we did a systematic analysis of all of our hazards, we could actually determine what they are, how far they are away from us, how soon they will get here, how long they will last. And we can map out what areas of our built environment would be in harm’s way.”

As Redmond noted, a major seismic event in Vancouver could entail a cascade of problems: the collapse of buildings and other structures; the rupture of oil and gas pipelines, or water and sewage pipes; the failure of power lines, roads and bridges; the release of hazardous materials; the liquefaction of alluvial soils in the Fraser River delta; and the spread of fires through areas inaccessible to firefighters, particularly if transportation infrastructure is compromised. Finally, the potential for a tsunami is real and grave.

The aftermath of the 2011 earthquake and tsunami that struck the Tohoku region of Japan illustrates Redmond’s point. The initial earthquake damaged buildings and infrastructure, including the Fukushima Daiichi nuclear power station, and liquefied soft soils near the shore. And although sea walls encircle approximately 40 per cent of the Japanese coast line, some over 10 metres in height, the structures offered little respite from the wave, in part because the earthquake had caused the land to subside. Despite a sophisticated tsunami warning system, rigorous building codes, and world-class standards of earthquake preparedness and response, more than 19,000 perished, and over 300,000 were displaced from their homes.

“In Japan, the buildings did very well during the earthquake; it was the tsunami that caused most of the devastation, and that tsunami was larger than what they were expecting in that part of Japan,” noted Cassidy.

“When the subduction earthquake occurs off our coast, we know that parts of Vancouver Island will subside, perhaps a half metre, perhaps one or two metres,” he added—a potentiality that governments and regulators need also take into account.

Redmond recommends mapping as many threats to communities as possible, adjusting land use patterns, and taking advantage of natural geographic features to help avert potential tragedies. But another significant hurdle, he said, is dealing with various levels of government. Elected officials and staff preside over different jurisdictions, and convincing parliamentarians to plan for events more than four years down the road is sometimes a challenge.

In B.C., for example, the province has domain over Crown lands, municipalities preside over zoning, and the federal government bears responsibility for First Nations.

“Imagine: You have all these jurisdictions, with their own bureaucracies, but you only have one fire. And the fire doesn’t read your plans.”

Although tsunamis and damage to buildings and infrastructure may accompany a massive quake, the majority of injuries related to seismic events, Redmond observed, owe to a less sensational cause: falling debris in the home, workplace, and school.

For individuals and families, Redmond has simple recommendations: avoid placing heavy items on high shelves, and keep two weeks worth of food and provisions on hand, including a flashlight and replacement batteries.

“Pretend you’re going on a long camping trip,” he said.

Source: http://www.vancouverobserver.com/city/old-buildings-coastal-areas-most-vulnerable-major-earthquake-bc

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