From personal experience, when a really big earthquake hits, it is extremely unnerving. In fact, my first earthquake was a magnitude 7.3 event in Southern California, and the serious shaking lasted not much more than 3 minutes.
However, it seemed like a lifetime to me then. If asked a week later, I probably would have said that it lasted at least a half an hour.
Look at the following diagram, taken from Wikipedia:
The P is what woke me up. It hit with a bang.
The S is what rattled and then broke the windows, and stutter-walked my bed 30 cm.
The R is what finally flipped me out of my bed and onto the floor.
It took several days for the information on this event to filter down through the scientists to the government entities, to the news media, to my parents, and then to me as a 6-yr-old child. By then we were back in our house, the power was restored, and we had water pressure again.
A Cascadia subduction earthquake might reach a moment magnitude 9+ when it next occurs. That will be at least 100 times more energy than the piddly 7.3 event that launched a sleepy 6-yr-old out of his bed in Bakersfield, California long ago. If I found a M=7.3 to be that terrifying, imagine how bad a M=9+ event will be.
There are two ways to deal with the terror:
#1. Understand immediately what is happening and what will come next.
#2. Be prepared for it. Know that you have your bases covered.
#2 is something that many people more or less do (some do OK, some do better, and some do extremely well at this):
A. Have a family plan in place. Where do we meet? What channels on the battery-powered, $40 hand-held walkie-talkies will we be using to find each other?
B. Have supplies at hand, including
i. Food. And don't count your refrigerator contents here.
ii. Water. A LOT more water than you might think.
iii. A battery-or-crank-powered Radio
iv. Batteries. Flashlights. LOTS of batteries.
v. Blankets and sleeping bags, and/or a heat source to keep warm.
C. Start checking up on your neighbors, and offer to share your stuff with them. People you may hardly know will become life-long friends really quickly.
However, the purpose of THIS blog entry or chapter is to help you deal with #1: understand what in the world is going on, so you don't go crazy.
Next, look at the following diagram: