[CEUS-earthquake-hazards] reply to Ellis Krinitzsky

[Wang, Zhenming]

Ellis and Klaus,

You both have brought up several important issues. Let's look over some of them.

As stated by Klaus, "probability and uncertainty are intrinsically connected through an underlying distribution, whether it is sampled sufficiently or not, simply by the fact that these distributions are linked to physical processes." In other words, in order to quantify uncertainty - estimating probability, an underlying distribution, such as normal, log-normal, or others, has to be used (or assumed). These can be seen through the probability estimates for the New Madrid earthquake by Seth and Chris. The different distributions (Poisson, Gaussian, lognormal) will give different probability estimates. However, this is not the case in PSHA. Here are two examples.

The following magnitudes and weights (probability, in parentheses):  7.3 (0.15), 7.5 (0.2), 7.7 (0.5), 8.0 (0.15) were used in the 2002 national seismic hazard maps. No underlying distribution was used or assumed in determining these probabilities (weights). In other words, these probabilities were arbitrarily assigned. Here, uncertainty is quantified by arbitrarily assigned probability.

Poisson distribution of earthquake occurrences is one of the fundamental assumptions that PSHA is based on (Cornell, 1968). And ground motion at a site is a consequence of an earthquake. Thus, ground motion occurrences at a site should also follow Poisson distribution. However, a lognormal distribution of ground motion (spatial) has been used to predict ground motion occurrences (temporal) (ergodic assumption). These are contradictory. The ergodic assumption can not be linked to a physical process.

These examples show that PSHA is not consistent with earthquake physics and statistics. Therefore, it is so difficult to understand the products from PSHA, and use of PSHA is problematic for engineering design and policy consideration. The problems related to the building codes have been discussed substantially on this listserver. Here is an example on the problems related to the critical facilities, nuclear facilities in particular.

A 10.0g (ten time gravitational acceleration) PGA design ground motion may have to be considered for the nuclear waste repository facilities at Yucca Mountain in Nevada based on a PSHA study. This is not a worst case scenario from PSHA.

Thanks.

Zhenming


___________________________________
Zhenming Wang, PhD, PE
Head, Geologic Hazards Section
Kentucky Geological Survey
228 Mining and Mineral Resources Building
University of Kentucky
Lexington, Kentucky 40506
Phone:(859)257-5500x142
Email: zmwang at uky.edu<mailto:zmwang at uky.edu>
Website: www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards>
____________________________________

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