Earthquake

Risk: Low-Moderate

Earthquakes may be described as “sudden movements of earth, caused by an abrupt release of strains that have accumulated over time along fault lines” (Coppola, 2011). Notably, many secondary hazards are triggered by earthquakes including landslides, rockslides, avalanches, and multiple utility failures from downed lines and collapsed pipes. Damage to buildings generally begins to occur at magnitude six while an earthquake above magnitude seven may be a major disaster if it occurred near a populated area. Although a low probability, if an earthquake were to occur, much of Squamish’s infrastructure would be at risk for structural damage. Ground shaking, liquefaction, and earthquake-triggered landslides represent the most significant earthquake related threats to Squamish (Journeay, 2011).

Mega-thrust earthquake:“This type of quake occurs, on average, every 500 to 600 years, but the intervals between events have been as short as100 to 300 years. Scientists have estimated that there is about a 12% chance of a similar magnitude quake in the next 50 years” (Auditor General of British Columbia, May 2014).

Shallow-focus earthquake: Shallow-focus earthquakes occur within the earth’s crust along fractures, generally at depths less than 35 kilometres. This class affects a smaller area than a deep earthquake of the same magnitude, but the shaking is usually more intense and aftershocks more numerous. The probability of a shallow crustal earthquake causing considerable damage in British Columbia has been estimated at approximately 12% in the next 50 years. To better understand these quakes, more information is needed about where the active faults are. (Auditor General of British Columbia, May 2014).

Deep sub-crustal earthquake: can occur as deep as 80km within the North American Plate, on which Squamish rests. Scientists estimate the frequency of deep sub-crustal earthquakes at about 60% in the next 50 years.

All development on flood plain land is vulnerable to liquefaction in the event of a shallow-focus seismic event. Our substantial commuter population risks being isolated from home and family if an earthquake closes Highway 99 on either side of DOS. Older building stock, including the Fire Hall and other critical public service infrastructure, are not earthquake resistant without strengthening work. There are limited reception centre options for evacuated people, including potentially high numbers of tourists/visitors.