Civil Engineering Reference
In-Depth Information
FIGURE 6.6
7.5 earth-
quakes. (
After Seed et al. 1985, reprinted with permission of the American Society of Civil Engineers.
)
Plot used to determine the cyclic resistance ratio for clean and silty sands for
M
the magnitude of the earthquake. As indicated in Table 2.2, the higher the magnitude of the
earthquake, the longer the duration of ground shaking. A higher magnitude will thus result
in a higher number of applications of cyclic shear strain, which will decrease the liquefac-
tion resistance of the soil. Figure 6.6 was developed for an earthquake magnitude of 7.5;
and for other different magnitudes, the CRR values from Fig. 6.6 would be multiplied by
the magnitude scaling factor indicated in Table 6.2. Figure 6.7 presents other suggested
magnitude scaling factors.
As discussed in Sec. 2.4.4, it could be concluded that the local magnitude
M
L
,
the sur-
face wave magnitude
M
s
,
and moment magnitude
M
w
scales are reasonably close to one
another below a value of about 7. Thus for a magnitude of 7 or below, any one of these mag-
nitude scales can be used to determine the magnitude scaling factor. At high magnitude
