[CEUS-earthquake-hazards] reply to Ellis Krinitzsky

[Oliver Boyd]

Hello Ellis,
I would like to respond to your comments and give Art some rest.

PSHA has been designed to account for uncertainty in earthquake ground
motions at a given site, both through aleatory uncertainty of ground
motions, which is built into the PSHA integral equations, and through
epistemic uncertainty of ground motions models and source models
(recurrence, magnitude, location, etc), which enters through logic trees. I
admit that the probabilistic method is more complicated than a deterministic
method, however...

What PSHA attempts to do is allow decision makers to assign a uniform and
acceptable level of risk. From a hazard curve at a site you can determine,
for example, what ground motions are expected to be exceeded with a 2%
probability in the next 50 years. This is an extremely useful measure for
decision makers. 

If you consider the worst case for each building or critical facility, they
would not be built to the same level of hazard or risk. Some structures
would be prepared for ground motions that might be exceeded once every 2,500
years while others might be prepared for ground motions that would be
exceeded once every 10,000 or 100,000 or 1,000,000 years. 

Preparing for relatively rare ground motions, though possible, would not be
efficient.

I hope this has addressed your comment.

Oliver

Oliver Boyd
Research Geophysicist
Geologic Hazards Team
U.S. Geological Survey
Memphis, TN