The Earthquake Threat in Southwestern British Columbia: A Geologic Perspective

Ten moderate to large (magnitude 6–7) earthquakes have occurred in southwestern British Columbia and northwestern Washington in the last 130 years. A future large earthquake close to Vancouver, Victoria, or Seattle would cause tens of billions of dollars damage and would seriously impact the economies of Canada and the United States. An improved understanding of seismic hazards and risk in the region has been gained in recent years by using geologic data to extend the short period of instrumented seismicity. Geologic studies have demonstrated that historically unprecedented, magnitude 8 to 9 earthquakes have struck the coastal Pacific Northwest on average once every 500 years over the last several thousand years; another earthquake of this size can be expected in the future. Geologic data also provide insights into the likely damaging effects of future large earthquakes in the region. Much of the earthquake damage will result directly from ground shaking, but damage can also be expected from secondary phenomena, including liquefaction, landslides, and tsunamis. Vancouver is at great risk from earthquakes because important infrastructure, including energy and transportation lifelines, probably would be damaged or destroyed by landslides and liquefaction-induced ground failure.