Giant earthquakes have repeatedly ruptured the Cascadia subduction zone, and similar earthquakes will likely also occur there in the near future. We employ a 3-D time-dependent thermomechanical model that incorporates an up-to-date description of the slab geometry to study the Cascadia subduction thrust. Results show a distinct band of 3-D slab dehydration that extends from Vancouver Island to the Seattle Basin and further southward to the Klamath Mountains in northern California, where episodic tremors cluster....