Tuesday, February 3, 2015
New USGS Seismic Hazard Map
I really hate to make fun of these things, since they are all-important and created by God-Kings.
Here goes: What is it? It is a map of Chance. If you were to throw an Earthquake Dart at it, the redder zones would have a magic attraction, making it more likely that the dart would land near there. It doesn't have to.
What are the units? Honestly, all this futzing is only good to 1 digit (log or decade), but everybody likes to quote to 1 percent. Epic battles have been fought over the exact placement of a line, sort of like climate science. The Big U only works with acceleration because that's what they do in California. I told them a million times that it doesn't work in the East, but do they listen? :)
Even if you used the right units, (PGV), there is the question of what ground conditions. You might want to uniformly use base rock, but the Miss. Valley doesn't have a rock in sight.
What is it good for? Not much, since every dang small town has its own building code. In Canada it is a bit more rational. For example, they've bumped up Oklahoma. Are they now going to put more nails in the framing?
But it is a pretty map, and totally centred on historical earthquakes. Enjoy.