Yet, over a period of weeks to months, these slow movements can release the equivalent energy of a regular magnitude-6.7 earthquake. At such depths, about 30 to 50 kilometers down, the rocks are too hot and deep for sudden shocks that people can feel. Various versions of slow earthquakes in Cascadia occur about 10 to 15 kilometers below where regular earthquakes strike. Today, different types of slow earthquakes tear at the subduction zone every 11 to 15 months without producing the jolt of a full-fledged, ground-shaking quake. and southwestern Canada, such tsunami-producing earthquakes have certainly happened in the past (see video below). However, for more than three hundred years, Cascadia has been quiet no modern seismic instruments have recorded megathrust earthquakes. When such large movements occur beneath the sea, the water’s displacement can cause devastating tsunamis. One day, the Juan de Fuca oceanic tectonic plate will suddenly lurch as it descends beneath North America, causing a massive earthquake that tears the seafloor. The Big One refers to a catastrophic megathrust earthquake likely to occur in the future. Scientists find strange slow quakes in Cascadia’s seismic gapįor residents of much of the northwestern coast of North America, the possibility of the Big One looms.
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