The sleeping giant offshore
Off the coast of British Columbia, the Juan de Fuca tectonic plate is sliding beneath the North American plate. This 1,000-kilometer-long fault, known as the Cascadia Subduction Zone, is a dormant fault. Geological evidence and Japanese tsunami records show its last major rupture was a magnitude 9 earthquake at approximately 9:00 PM on January 26, 1700. This single event caused parts of the coastline to drop by several feet and sent a tsunami across the Pacific Ocean.
Megathrust earthquakes of this scale have occurred along the zone roughly every 500 to 600 years on average, though the interval can be as short as 200 years. More than 300 years have passed since the last one, meaning immense strain is building along the locked fault. Scientists estimate there is a 10 to 15 percent chance of a magnitude 9+ event rupturing the entire zone within the next 50 years. Such a quake would generate intense shaking for several minutes. To provide important time for self-protection and automated safety measures, Canada has developed a national Earthquake Early Warning (EEW) system, operated by Natural Resources Canada (NRCan).
A race against seismic waves
The warning system doesn't predict earthquakes; it detects one that has already started and outraces the damaging seismic waves. An earthquake releases two main types of waves: the faster, non-damaging Primary (P-waves) and the slower, destructive Secondary (S-waves). P-waves travel at about 6 kilometers per second, while S-waves move at roughly 3.5 kilometers per second.
A network of over 400 sensors across British Columbia, including critical seafloor instruments placed directly over the subduction zone, detects the initial P-wave. Instantly, data is transmitted to processing centers where algorithms determine the earthquake's location and estimate its magnitude. If the quake meets the threshold for potentially damaging shaking, an alert is broadcast through Canada's National Public Alerting System to phones, TV, and radio. The time gap between the P-wave detection and the arrival of the S-waves is the warning time. Adding seafloor sensors to the land-based network can increase warning times by nearly 50 percent for coastal communities. For a major offshore quake, this can mean 30 seconds of warning for Vancouver and up to four minutes for areas farther from the epicenter. Those seconds allow people to "Drop, Cover, and Hold On" and enable automated systems to slow trains, stop traffic from entering bridges, close gas valves, and open fire station doors.