Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 231

Effects of all
wave types
(a)
Effects of S, L
and R wave types
(b)
Effects only of L and
R wave types
(c)
Figure 7.11 Accelerogram types in function of the distance from the epicenter:
(a) Near-source area; (b) Intermediate-field area; (c) Far-field area
(after Filiatrault, 1996)
In case of crustal sources, the source-site distance plays a leading role,
considering that the attenuation is very different for the different wave types.
Attenuation is very high for the P-waves, moderate for S-waves, and reduced for
surface waves. Figure 7.11 presents the recorded acceleration types for near-source
sites, where all the wave types are present, for intermediate-source sites, where the
P-wave disappears due to the very important attenuation, and for the far-source
sites, where the surface waves only remain (Filiatrault, 1996).
Therefore, in function of source-site distance the following site classification
may be considered (Fig. 7.12):