Quaternary Geology and Liquefaction Susceptibility, San Francisco, California 1:100,000 Quadrangle: A digital database

Earthquake-induced liquefaction has historically caused loss of life and damage to property and infrastructure. Observations of the effects of historical large-magnitude earthquakes show that the distribution of liquefaction phenomena is not random. Liquefaction is restricted to areas underlain by saturated, loose, cohesionless sand and silt. Areas susceptible to liquefaction can be delineated on the basis of geologic, geomorphic, and hydrologic mapping and map analyses (e.g., Youd and Perkins, 1987; Tinsley and Holzer, 1990; Sowers and others, 1995). Once liquefaction susceptibility zones are delineated, public agencies, private organizations, and individuals can prepare for and mitigate liquefaction hazards in these zones.
The study area includes the San Francisco Peninsula, the eastern San Francisco Bay area, and part of the northern San Francisco Bay area, including the cities of Burlingame, Concord, Oakland, Richmond, San Francisco, San Mateo, San Rafael, and Walnut Creek (Figure 1). Holocene estuarine deposits, Holocene stream deposits, Holocene eolian and beach deposits, and artificial fill are widely present in the region (Plate 1), and are typically the geologic materials most susceptible to liquefaction. Major faults capable of producing large earthquakes cross the study area, including the Concord, Hayward, San Andreas, and San Gregorio faults (Figure 1). These earthquakes expose the entire study area to long-duration ground motions with peak ground accelerations in excess of 0.2 g, sufficient to trigger liquefaction in highly susceptible natural deposits and artificial fill.