At the scale of the Pacific Plate it isn't one rigid piece but more of a soft plastic plate. Sure, movement in one area changes stress in other boundaries but t

At the scale of the Pacific Plate it isn't one rigid piece but more of a soft plastic plate. Sure, movement in one area changes stress in other boundaries but there are quite a few more inputs and outputs like the diverging boundaries spanning the east side of the Pacific Plate (Juan de Fuca, Explorer Ridge, Galapagos Rise, East Pacific Ridge, Pacific Antarctic Ridge are a few). Some of these are more responsible for the Ring of Fire than the Pacific Plate boundaries: the other end of the Juan de Fuca plate is the Cascadia Subduction Zone and the Nazca Plate as part of the Andean orogeny to name two. Significant earthquakes can be produced by motion that isn't aligned with the general east to west movement of the Pacific Plate. Fault structures around the plate boundaries, fault complexes associated with the bordering plates (North America, South American, Antarctic, etc), and localized stress associated with subduction and volcanoes all produce large earthquakes. This research includes at least one of these quakes (Landers).