Up until a decade or so ago, the region was considered very safe in terms of earthquake, based on the historical lack of any incidence (since the European settlement). Unknown until then that a fault was capable of storing all the accumulated stress of many century as uplift strain, without any release between major quakes.
California’s experience with structural damage at that time wasn’t considered applicable to points north. Now, only Japan’s engineering experience with severe events comes close to the expertise appropriate to building codes in the northwest.