The Marina District of San Francisco suffered from relatively intense shaking and liquefaction in the 1989 Loma Prieta earthquake. The soft bay and marsh soils in the area, which were covered by dredged sand in the early 1900s, amplified earthquake shaking. The sandy fill material liquefied, causing disruption of streets, sidewalks, telephone and power poles and homes. Here, the liquefied sand decoupled the overlying fill and structures from the underlying sediment, allowing the overlying materials to oscillate with shaking that continued after the fill material liquefied. In such "ground oscillation" permanent deformations may be small, but displacements during earthquake shaking may be damaging (Youd, 1995). (U.S. Geological Survey photograph)

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