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not available for many case studies, they chose to express the LSI in terms of earthquake
magnitude, M, and the log of the distance from seismic energy source, R, by the following
equation:
log LSI = -3.49 - 1.86 log R + 0.98 M w (4-5)
where
LSI is the maximum expected permanent horizontal displacement, in inches;
R is the shortest horizontal distance measured from the surface projection of the
seismic energy source or fault rupture to the site of interest, in kilometers; and
M w is the moment magnitude.
The LSI data are plotted on Figure 4.6. Cases where the maximum horizontal ground
displacement exceeded 2.5 m were excluded from the derivation of the LSI equation. There is
large uncertainty in estimating these extreme displacements, and they are well beyond tolerable
limits for bridges. Therefore, they are not particularly meaningful for engineering purposes.
Figure 4.6: Variation of LSI with Distance and Earthquake Magnitude (Youd and Perkins 1987)
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