The crucial bridges that connect Portland as well as the major Interstate that acts as an entry and exit to the city for escape and resources would likely collapse. The ability to get in and out of the city would be almost impossible.
Many of the Portland roads are build on alluvial deposits, meaning they will probably crack and sink into the ground.
All of the city's road-clearing equipment is stored under the Fremont Bridge ramps, which is also likely to collapse.
Finally, most of Portlands fuel supply is obtained by a BP pipeline that runs beneath the Columbia and Willamette Rivers, which would likely rupture in the event of an earthquake, leaving catastrophic leakages and leaving Portland without fuel. Any incoming fuel by truck would be stuck at the collapsed freeway entries.
This lack of transportation will leave hundreds of thousands of people stranded, without food or water (unless they planned properly), without electricity for months. Those who are greatly injured would not have easy access to any medical facility by car as the city would be an absolutely battle ground of rubble. The broken bridges, roadways, freeways etc, and lack of necessary equipment for cleanup and transport would leave Portland in a state of emergency.