Reducing risk from crustal earthquakes in western Canada

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Western Canada is subject to the greatest seismic hazard in Canada. Some of the world's largest earthquakes have occurred in this region, including the magnitude (M) 9 Cascadia subduction earthquake to the west of Vancouver Island in 1700; the M=8.1 earthquake just to the west of the Queen Charlotte Islands in 1949; and the M=7.9 Denali Fault earthquake in Alaska, which ruptured to within 100 km of the Yukon border. Other large, damaging crustal earthquakes include the 1918 M=7 event and the 1946 M=7.3 event, both on Vancouver Island, and the M=7 earthquake just south of the Fraser Valley in 1872. These crustal earthquakes pose a threat to the population centres of southwest BC, and also to critical infrastructure throughout western Canada, including pipelines in the Yukon and NWT, hydroelectric dams and transmission infrastructure throughout western Canada, and port facilities in BC. The importance of understanding crustal earthquakes was demonstrated by the M=6.9 Kobe, Japan earthquake that caused more than $300B dollars in damage. However, crustal earthquakes in western Canada are enigmatic. There are large-scale crustal faults, such as the Denali Fault, Tintina Fault, and Fraser Fault - however no significant amount of seismicity has been observed on these structures during historic times. In southwestern BC, where large crustal earthquakes have occurred (e.g., 1946 central Vancouver Island) - there is no evidence for surface faulting, and so the "active fault" may be hidden at depth. The long-term goal of this proposed research is to better understand crustal earthquakes in western Canada - where can they occur, how large can they be, how often might they occur, and how will the ground shake. We will do this by identifying active structures, mapping the slip distribution and rupture process along faults, and mapping the earthquake-generating stress field. The results of these studies will be incorporated into seismic hazard maps in the National Building Code of Canada, and will provide waveforms useful for engineering applications. This, in turn, will help to minimise losses and economic impact of future earthquakes in this region. The benefits to society from this type of research can be in the billions of dollars.