Seismic Ground Motion - Dynamic Behavior of Concrete and Seismic Engineering - page 119

Maximum values
Figure 3.6. Example of the appearance of site effects in the time field. RAP recordings of
25 February 2001 (M =4.7) earthquake in the city of Nice. The “Mont-Boron” station is
on rock, whereas the four others are on the Paillon's alluvial deposits; the “Alsace-
Lorraine” station is the thickest
It is almost impossible to give general indications, as the effects depend too
much on the position of the frequency band amplified in comparison with the
incident spectral content. For example, a site that is not very thick (high f 0 ) may give
rise to strong PGA amplification during a moderate earthquake nearby, but no
particular effect during a wide amplitude earthquake far away - even if the absolute
incident PGA levels are identical! Conversely, very thick sites may not affect, or
even reduce, the PGA during moderate earthquakes nearby, yet amplify it
considerably for those far away, while the transfer functions remain unchanged.
3.4.3.2.5. Duration
Because motion duration is rarely taken into account in paraseismic design, few
attempt at quantifying the consequences of resonance and trappings on duration
have been published. From a qualititative point of view, however, valley and basin
configurations seem to prolong motions in a significant way ([BEA 03], [COR 03],
[PAR 03]). The study of prolongation may even constitute a good method for
detecting the presence of 2D or 3D effects (Figure 3.6).
3.4.3.2.6. Modifications due to non-linearity
As with most other materials, grounds deteriorate when subjected to high
mechanical stresses: as shown by [SEE 69]'s pioneering works, the secant stiffness