Earthquakes - Geotechnical Engineering Investigation - page 974

Minimum fault lengths in terms of site distance requiring detailed study are given in Table
11.16. The potential magnitude may be estimated from the length of the capable fault (or
faults) as given in Figure 11.27 or Equation 11.18. Assumptions regarding rupture length
have varied by practitioners from one half to one third of the total (Adair, 1979).
When the information is available, all faults within some specified distance from the site
should be identified in terms of distance, maximum magnitude of events, and fault type.
Some relationships between construction damage for maximum source to site distances in
terms of site acceleration, magnitude, and intensity are given in Table 11.17. Fault type is
important since it has been found that for vertical or dipping faults the direction of rupture
propagation in the near field can cause significant differences in the level of shaking for dif-
ferent orientations relative to the fault's strike ( Section 11.3.1, Dip-slip Displacement).
Control width : The NRC (1997) requires an evaluation for a specific fault of potential
rupture width (Equation 11.19) and potential rupture area (Equation 11.20). Note that
Equations 11.18-11.20 were developed for sites in the western United States. The control
width of a fault is defined (NRC, 2003) as the maximum width of the zone containing
mapped fault traces. These include all faults that can be reasonably inferred to have expe-
rienced differential movement during Quaternary times and that can join or reasonably
be inferred to join the main fault trace, measured within 10 mi along the fault's trend in
both directions from the point of nearest approach to the site, as shown in Figure 11.45.
The control width requires detailed investigation for a specific Nuclear Power Plant loca-
tion. The zone width requiring detailed study vs. the potential earthquake magnitude is
given in Table 11.18.

TABLE 11.16
Minimum Fault Length to Be Considered in Establishing Safe-Shutdown Earthquake a

Distance from Site (mi) Minimum Length (mi)

0 - 20 1

Greater than 20-50 5

Greater than 50-100 10

Greater than 100-150 20

Greater than 150-200 40

a

From NRC, Appendix A to Part 100, U.S. Nuclear Regulatory Commission, 2003.

TABLE 11.17
Source to Site Distance for Earthquake Damage

Earthquake

Maximum Distance

Minimum Site Richter Modified Earthquake

Damage to Construction Acceleration ( g ) Magnitude Mercalli intensity Source to Site (km)

Stable foundation 0.15 6.0 VIII 20

0.15 7.0 X 32

0.15 8.0 XI 50

Soil liquefaction, 0.10 5.3 VII 1

permanent ground 0.10 6.0 VIII 10

displacement 0.10 7.0 X 50

0.10 8.0 XI 150

Seismic-wave 0.05 7.0 X 230

amplification in soft soil 0.05 8.0 XI 400

Maximum distance for damage to good construction (mean excitation) in western U.S.
From Civil Engineering , ASCE, November 1993.