displacements can literally rip structures apart. Lateral spreading tends to allow material to fill topographic depressions, such as streams and rivers, causing the channels to narrow and the flow to become dense—a major source of damage to bridges during earthquakes (22). A more recent case of lateral spreading occurred during the August 17, 1999, Izmit, Turkey earthquake (M 7.4) when unconsolidated, water-saturated deltaic sediments collapsed into the sea (Figure 3.5), resulting in numerous deaths. Lateral spreading or landsliding can also be caused by the shaking-induced loss of shear strength in certain types of “quick” or “sensitive” layers of salt-leached, clay-rich marine sediments. The spectacular damage to the Turnagain Heights district of Anchorage during the great 1964 earthquake (M 9.2) (Box 2.3) has been attributed to large (150- to 180-meter) displacements within a relatively thin zone of the Bootlegger Cove clay, 25 meters below the surface (23).
Empirical relations for predicting the extent and severity of liquefaction events have been developed through field studies, theoretical modeling, and laboratory experiments using geotechnical centrifuges. Less ex-