Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 245

Figure 7.24 Mode of lateral permanent ground displacement (after Scawthorn,
1997)

The liquefaction effect is more significant for the strong earthquakes with long
duration (large number of cycles). The minimum values of earthquake magnitude
and peak acceleration required to generate liquefaction in function of soil
characteristics are the following (Youd, 2003):

Magnitude Acceleration for Acceleration for

stiff sites soft sites

M < 5.2 < 0.4g < 0.1g

5.2 < M < 6.4 < 0.1g < 0.05g

6.4 < M < 7.6 < 0. 05g <0.025g

M > 7.6 < 0.025g <0.025g

It is very clear that for low and moderate magnitudes, the influence of site type
is very important. Contrary, for strong earthquakes, the influence of site type is
insignificant. This means that the site type plays a very important role in the case
of intraplate earthquakes.

7.4.7 Six-degree-of-freedom Ground Motions

The general motion of a body is uniquely specified by three components of
displacement and three components of rotation. Nevertheless, it is standard to
observe only translational motions and the study of rotations in the context of
earthquakes has little attention, partly because rotational effects generated by