Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 243

(b)
Figure 7.22 Effects of alluvial valley: Increasing of accelerations (after Panza et al,
1999)
The thick low velocity deposits (alluvium sands and clays poorly consolidated with
high water content) are responsible for large increment of the acceleration values
inside the basin, explaining the anomalous high micro-seismic intensity caused by
the 1976 Tangshan earthquake (with magnitude M 7.8).
7.4.6 Liquefaction
The destructive power of liquefaction was abruptly brought to the specialists'
attention by the two large earthquakes that occurred in 1964, the Great Alaskan (M
9.2) and Niigata (M 7.5). The liquefaction during the Alaskan earthquake produced
large damage in highway and railway bridges. During the Niigata earthquake, the
liquefaction phenomenon reduced the bearing capacity beneath many buildings,
causing settlement and tipping (Youd, 2003). The seismic liquefaction of soils was
noted in numerous other earthquakes: 1811-1812 New Madrid (producing the
greatest seismic effects in the USA), 1989 Loma Prieta (USA), 1995 Kobe (Japan)
and 1999 Kocaeli (Turkey).
In common usage, liquefaction produces the loss of strength in saturated,
cohesionless soils due to the build-up of pore water pressures during dynamic