Slope of Hazards Curve

DOE-STD-1024-92

As shown in Table 3 of the Standard, representative peak ground

acceleration values are equal to or lower than the previous estimates from

UCRL-15910 (DOE-STD-1020). These results suggest that median seismic

hazard estimates have decreased since the late 1970's. Table 3 also

shows that the recommended values are equal to or greater than the EPRI

85th but significantly lower than the LLNL 85th.

Due to the results above, the revised Standard recommends for Eastern

sites with both the LLNL and EPRI probabilistic seismic hazard results

either the continued use of the TERA Inc. seismic hazard values or the use

of the approach outlined in the Standard itself.

Comparisons to the NEHRP vibratory ground motion maps have not been

completed due to the fact that the seismic hazard data contained in the

NEHRP map is relatively old particularly compared to the LLNL and EPRI

seismic hazard data, and the NEHRP values are for rock site conditions

which are not directly comparable to the LLNL and EPRI results.

SLOPE OF HAZARD CURVE

(NS-3, LLNL-4, LLNL-5, LLNL-9, OR-3, EH-2, RW-5)

The slopes of the EPRI and LLNL seismic hazard curves were reviewed as

part of developing the revised Standard. This review found that the hazard

curve slopes are dependent on probability.

In order to compensate for the differences in slope values at different

ground motion levels, separate slope values have been calculated for PGA

at various hazard probabilities. A slope value of 2.58 is calculated from a

composite ratio of PGA at 10-5 to PGA at 10-4 and a value of 1.93 is

calculated from a composite ratio of PGA at 10-4 to PGA at 10-3. Correlating

these probability values to those used in UCRL-15910 (DOE-STD-1020),

the slope value of 1.93 is used for low hazard and moderate hazard

facilities while the slope value of 2.58 is used for high hazard facilities. The

revised Standard provides a detailed discussion of this issue.

DIFFERENT PROBABILITIES AFFECTING CORRECTION FACTOR

(NS-4, NS-5, LLNL-5, RW-2, RW-5)

In addition to the changes in the slope values mentioned above, the revised

Standard also calculates different correction factors for different facility

hazard categories (the term hazard category as found in UCRL-15910,

(DOE-STD-1020)). Correction factors are calculated at various PGA levels

using the different slope values. From Table 2 in the body of the

recommendation, median values of ground motion range from .03g to .10g

for 10-3 and from .07g to .22g for 2 x 10-4 for DOE EUS sites. Therefore, for

Low Hazard and Moderate Hazard, a PGA value of .10g is used and for

High Hazard facilities, a PGA value of .20g is used. Appendix E to the

Standard provides the set of LLNL and EPRI data that was used to develop

the correction factors. Appendix E displays the impact of the different

A-23