"it would seem the whole of the Pacific coast, from San Diego to anchorage, is at risk of unprecedented near term seismic activity of colossal scale. How do you engineer infrastrucutre for force 9+ events?"
You don't. I suspect that you know this :-)
Here's my thoughts. First, I had a long personal discussion with a seismologist on this topic. Can earthquake faults link up and produce massive quakes? Her answer was No ... this does not happen. The ruptures are mostly small, random breaks at various locations around the world.
I remain skeptical about this. But I do understand that earthquake scientists must GO with the data that they've got. Science is not about speculation. And really, we have not been measuring earthquakes for very long. If our scientists had been collecting quake data for 50,000 years, their knowledge would be tremendously good.
I think that most of the time, the quakes probably are small random events. But I suspect that every once -and-a-while something much bigger can occur. It's just rare, and we haven't seen it yet. If I look at the southern San Andreas, there's a history of quakes every 100-150 years. Quakes in the range of 6.5 to 7.5, something like that. There have been about 8-9 quakes like that, going back over 1,000 years or so. We are now at a situation where the time delay has gone close to 300 years. I would have to go and check that data again. But it is VERY long compared to the normal pattern. There is a LOT of energy stored in the ground. My gut instinct tells me ... is it possible we can see something much bigger happen? Are we at the point where we could see a rare event, that only happens every few thousand years? Yeah - MAYBE. But of course, we don't know.
If a major rupture happens across ALL of California, or maybe part of California and all of Oregon, it will be one big mud patch out there :-)
But who knows?
Pete