Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 248

- Incoherence effect : loss of coherency of seismic waves due to scattering in
heterogeneous medium of ground and superposition of the waves arriving
from different point of the source, which is extended on a surface;
- Wave-passage effect : differences in the arrival time of waves at different
surface points;
- Attenuation effect : gradual decay of wave amplitude with the distance due
to geometric spreading and energy dissipation in the ground medium;
- Site-response effect : spatially varying local soil profiles and the manner in
which they influence both amplitude and frequency content of the ground
motion underneath each surface point.
These variations in ground motions produce differential motions of building
foundations. The estimation of the effects of these motions on the structural
response suggests that such effects are usually small. However, in the near-source
areas, where the amplitudes of ground motions are large, and in the soft soils, the
effects can be significant.
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Figure 7.26 Wave effects: Torsional excitation of columns by passage of Love
waves and Rocking excitation by passage of Rayleigh waves (Gioncu and
Mazzolani, 2002)