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Study Predicts Results of Canadian Seismic Events

Aerial view map of Canada
Earthquakes measuring at a magnitude 5.0 on the Richter scale or higher have occurred within Canada, yet some are concerned that the country is not as well prepared for the next large earthquake as it might be. Future earthquakes on the west coast or to the east could potentially impact 40 percent of the national population, according to a new report. Insurance Bureau of Canada and AIR Worldwide

A scientific report released last month underscores the potential for billions of dollars in damage that could be caused by major seismic events in Canada.

November 19, 2013—Approximately 4,000 earthquakes are recorded in Canada each year. While most are small, mild quakes, the potential for major seismic events is a very real possibility on both sides of the nation. In an effort to jump-start the conversation about earthquakes in Canada, the Insurance Bureau of Canada (IBC) commissioned Boston-based AIR Worldwide to complete a scientific study to establish how much damage could potentially be caused within the country should two major seismic events occur—a magnitude 9.0 event on the Richter scale on the west coast, and a magnitude 7.1 event centered in the east.

“The purpose of the study was to try and get a better handle on if there were to be an earthquake of a significant magnitude—a magnitude that is scientifically possible—what would that look like in Canada? Because from a policy perspective, that discussion has not advanced very far,” says Chris White, the vice president of federal affairs for the IBC.

In both scenarios, the potential damage was assessed within a latitude-based grid system that created approximately 1 km2 sections, according to the report. This enabled the study to focus on the potential damage to specific building types and infrastructure within those sections that might be caused by ground motion and resulting land-mass reactions (for example, liquefaction and landslides) within each plot.

For the western scenario, the epicenter of the hypothetical magnitude 9.0 event was presumed to be located along the Cascadia Subduction Zone, approximately 75 km off the west coast of Vancouver Island and at a shallow depth of 11 km. This was determined to be a reasonable potential event for this zone, according to the report: The last major rupture of the Cascadia Subduction Zone was a magnitude 9.0 “megathrust” earthquake in 1700.

Overall, the western scenario earthquake, with an epicenter 300 km from the city of Vancouver, was assessed to cause CAD$75 billion (U.S.$72 billion) in damage. The most significant damage would be caused by ground motion, which would especially affect unreinforced masonry buildings (particularly heritage and vintage buildings), as well as tall buildings, bridges, and pipelines that were not engineered to withstand such effects. Road and bridge closures could extend from a few days to much longer. The report also noted that certain specific areas would potentially be impacted by flooding from the modest tsunami that would be generated by the earthquake, as well as by liquefaction, landslides, and potential fires.

Along the east coast, the hypothetical event was a magnitude 7.1 inland earthquake with an epicenter almost 100 km northeast of Québec City along the Charlevoix Seismic Zone. The hypothetical earthquake was centered underneath the St. Lawrence River at a shallow depth of 10 km. Although the Charlevoix Seismic Zone has not experienced a major event in the 21st century, it has seen at least one event measuring magnitude 5 or higher each century for the four centuries preceding this one, according to the report.

Despite the fact that the eastern scenario involved a much lower magnitude earthquake than the western scenario, due to its closer proximity to Québec City, the level of damage and shaking experienced by residents in both events is comparable, according to the report. In the eastern scenario CAD$61 billion (U.S.$58 billion) in damages would be caused, mostly due to violent shaking. Much of the damage would focus on unreinforced masonry buildings, particularly historic ones, some of which would experience complete total destruction. Highway and rail bridges in some areas would suffer moderate to extensive damage, and outages of electrical telecommunications services would occur and would be expected to last, at minimum, a number of days, according to the assessment.

In both scenarios, modern buildings and structures that have been built to current seismic codes would perform relatively well during the earthquakes, according to the report.

“Even though 40 percent of [the] Canadian population lives in these regions, the awareness [of] the potential loss from a major earthquake seems to be low,” said Oh-Sung Kwon, Ph.D., M.ASCE, an assistant professor of civil engineering at the University of Toronto, who calibrated the seismic fragility functions for the report. Kwon wrote in response to written questions posed by Civil Engineering online. “I think it is probably due to the fact that the country has not experienced a major damaging earthquake in the past decades.

“From an engineering standpoint, it is necessary to understand the seismic fragility of structures considering the design codes and construction practices of a specific region,” Kwon said. “There have been many studies on seismic fragility of structures, but it is hard to find research results in which a homogeneous and engineering-based method is applied to evaluate the fragility of structures in a regional basis.”

The current report on Canada’s risk is intended to raise awareness of the impact of a major seismic event in Canada by providing information that government agencies, regulators, disaster preparedness organizations, and the insurance industry can use to plan for, and mitigate the risk of, future earthquakes, according to the report.

Major, damaging seismic events that occurred in the United States in the 1980s and 90s—such as Coalinga (1983), Whittier Narrows (1987), Loma Prieta (1989), and Northridge (1994)—brought attention to the need to prepare for seismic disasters in order to mitigate risk, according to Kwon. “Based on the experiences from the earthquakes, the government and emergency management agencies have developed several research programs and mitigation plans,” Kwon said. Such mitigation efforts include California’s Senate Bill 1953, known as SB1953, which was introduced and passed in 1994, in the aftermath of the Northridge earthquake, and which required the seismic retrofit or replacement of all acute care hospital buildings in the state of California deemed to be at risk of collapse during an earthquake. The law required that if a given hospital could not be seismically updated as required, it must remove acute care services from its functions.

The Insurance Bureau of Canada hopes to bring attention to the need for further preparation within Canada before a major seismic event actually strikes. “We just have to work with government to make sure that from a public policy perspective, we find a way to more effectively educate consumers,” White says. “[And] we need to find a way to make sure that the industry is better prepared and government is better prepared.”

British Columbia is already seismically strengthening its schools in preparation for a major seismic event, but additional large-scale retrofitting efforts could be undertaken. “The report by AIR Worldwide and IBC will awaken people that [an] earthquake could lead to significant societal loss [in Canada], which will lead to open discussions to develop mitigation plans,” Kwon said. The methodology developed in the study could also lead to more fine-grained studies that would help prioritize the retrofitting of bridges or essential structures in specific locations, he said.



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