Lateral Spreads
Lateral spreads involve lateral displacement of large, superficial blocks of soil as a result of liquefaction of a subsurface layer.
Displacement occurs in response to the combination of gravitational forces and inertial forces generated by an earthquake.
Lateral spreads generally develop on gentle slopes (mos t commonly less than 3 degrees) and move toward a free face such as an incised river channel. Horizontal displacements commonly range up to several meters.
The displaced ground usually breaks up internally, causing fissures, scarps, horsts, and grabens to form on the failure surface.
Lateral spreads commonly disrupt foundations of buildings built on or across the failure, sever pipelines and other utilities in the failure mass, and compress or buckle engineering structures, such as bridges, founded on the toe of the failure.

Diagram of a lateral spread (Youd, 1992).

(Fig. 3). [after EERI]

Damage caused by lateral spreads is severely disruptive and often pervasive.
For example, during the 1964 Alaska earthquake, more than 200 bridges were damaged or destroyed by spreading of floodplain deposits toward river channels.
The spreading compressed the superstructures, buckled decks, thrust stringers over abutments, and shifted and tilted abutments and piers.
Lateral spreads are particularly destructive to pipelines. For example, every major pipeline break in the city of San Francisco during the 1906 earthquake occurred in areas of ground failure. These pipeline breaks severely hampered efforts to fight the fire that ignited during the earthquake; that fire caused about 85% of the total damage to San Francisco. Thus, rather inconspicuous ground-failure displacements of less than 2 m were in large part responsible for the devastation that occurred in San Francisco (Youd and Hoose, 1978).

Ground Oscillation
Where the ground is flat or the slope is too gentle to allow lateral displacement, liquefaction at depth may decouple overlying soil layers from the underlying ground, allowing the upper soil to oscillate back and forth and up and down in the form of ground waves (Fig. 4).
These oscillations are usually accompanied by opening and closing of fissures and fracture of rigid structures such as pavements and pipelines. The manifestations of ground oscillation were apparent in San Francisco's Marina District due to the 1989 Loma Prieta earthquake; sidewalks and driveways buckled and extensive pipeline breakage also occurred.