Even in a place like Portland, most of the lateral structural design is driven by wind loads, and not earthquakes. (And if you want to hear a great podcast about a real New York skyscraper that actually could have blown over in the wind, I recommend
this episode of 99% invisible.)
Seismic design gets more complicated with every irregularity in the shape of the building - i.e., a rectangular building (such as PAW) is easier to design for than an "L" or "H" shaped building. If the shear walls don't align floor-to-floor, then that's a problem too, but in this case the core is acting as the shear walls, and runs straight up and down the building. I would imagine imagine that most of the seismic design was specifying appropriate connections - i.e., how does steel connect to concrete, etc.