subduction

Predicting the exact arrival of a Cascadia Subduction Zone quake is also nearly impossible, and constantly evolving.

The Cascadia Subduction Zone is the wonky name for the place where all this mayhem will begin.

Subduction zones are found where one plate overrides, or subducts, another, pushing it downward into the mantle where it melts.

There are three types of plate boundaries: spreading zones, transform faults, and subduction zones.

Most faulting along spreading zones is normal, along subduction zones is thrust, and along transform faults is strike-slip.

And from hence lastly doth arise the solidity of the section, by addition and subduction.

The lines with barbs show zones of underthrusting (subduction), where one plate is sliding beneath another.