Risk Engineering, Inc. Summary Issues

DOE-STD-1024-92

other estimators, such as the median. Median estimates of seismic

hazard appear to be stable estimators of the seismic hazard at a site;

The number and weights assigned to ground motion models used in

the LLNL and EPRI studies are very different. There is a larger

number of models encompassing a large range of opinions in the

LLNL study compared to the EPRI study; and

Lawrence Livermore National Laboratory found that the probability of

exceedance of a given ground motion value is, in general, close to a

lognormal probability distribution. The EPRI distribution of the hazard

appears to be skewed strongly toward the low probability of

exceedance. A key difference between the two studies relates to

differences in the way that the expert opinion was elicited, particularly

with respect to uncertainty assessments.

2.1.2 Risk Engineering, Inc. Summary Issues

Risk Engineering, Inc. found that the uncertainty provided by a

given expert in the LLNL study was much larger than the

uncertainty provided by the EPRI expert teams. Risk Engineering,

Inc. concluded that there were unrealistically large uncertainty

bands on seismicity parameters for four of the LLNL seismicity

experts, particularly for the Charleston seismic source zone. One

seismicity expert (in one extreme case) included a recurrence

interval of 20 days for a magnitude greater than 5.0 for the

Charleston source. This same expert had an upper end to the

recurrence range for magnitude 5.0 of 2290 years, which is longer

than the recurrence estimates for the 1886 Charleston event;

Risk Engineering, Inc. concluded that there was insufficient

feedback to allow comparison of the resulting LLNL seismicity

expert interpretations with historic seismicity data. In general, the

recurrence intervals for all of the LLNL seismicity experts may be

anomalously short when compared to historic seismicity;

Risk Engineering, Inc. has also -found that the EPRI team of

Dames and Moore does not fully account for historic seismicity near

the Savannah River Site (SRS). One reason for this is the fact that

the SRS host source zone was given a low probability of activity.

Risk Engineering, Inc. recommended that the Dames and Moore

seismic source input not be used to calculate the seismic hazard at

SRS;

Risk Engineering, Inc. has compared the attenuation functions

selected by EPRI and the LLNL attenuation experts with available

strong motion data in the Eastern North America, and in particular