The Cascadia Subduction Zone

The Cascadia
Subduction Zone

Executive Summary:

The significance of the Cascadia Subduction is that the Juan de Fuca plate is submerged under the coastal waters of the Pacific Ocean along the western edge of the North American Plate. A subduction is a condition where one plate pressing against another plate distorts and either climbs over the other plate, forming a mountain range, or dives under the opposing plate. The Juan de Fuca plate at the Cascadia subduction dives under the North American Plate. The subduction causes extreme pressures both pushing against but also bending a flexing against the larger plate. When the fault line between the two slip to release some pressure it creates significant to catastrophic seismic events.

The proximity to the heavily populated areas or British Columbia / Vancouver, Canada, Washington, Oregon, and the Northern section of California, means that any significant "kick" or slippage of the folded crust along could result in 9-10 magnitude earthquakes and potentially several hundred foot high tsunamis. The devastation would be biblical.

The fact that the subducting plate consists of significant amounts of water saturated material (dirt, silt, sand, etc.) it is taking that under the earth's crust with the plate. When that "wet earthen material" comes into the underlying magma chamber, it produces steam. The steam builds pressure underground like a tea kettle getting ready to whistle. In this case the whistle would be a volcanic or super-heated steam geyser explosion.

Supporting Detail:

According to the USGS, "The subduction of the Juan de Fuca plate beneath North America changes markedly along the length of the subduction zone, notably in the angle of subduction, distribution of earthquakes, volcanism, geologic and seismic structure of the upper plate, and regional horizontal stress."

In "English" that means; The Juan de Fuca plate seems to be cracked across the upper portion. As a result, the plate is "diving" below the North American Plate at different angles. The difference in the angles are remarkable. As you can see from the images below, the section of the plate diving under Vancouver Island is descending on much more shallow angle than that of the section which is diving under Oregon.