|Qhc||Modern stream channel deposits|
|Qhbm||Holocene bay mud|
|Qhs||Holocene dune and beach sand|
|Qhb||Holocene basin deposits|
|Qht||Holocene terrace deposits|
|Qhf||Holocene alluvial fan deposits|
|Qhl||Holocene alluvial fan levee deposits|
|Qha||Holocene alluvium, undifferentiated|
|Qf||Late Pleistocene to Holocene fan deposits|
|Qa||Late Pleistocene to Holocene alluvium, undifferentiated|
|Qpf||Late Pleistocene alluvial fan deposits|
|Qpa||Late Pleistocene alluvium, undifferentiated|
|Qps||Late Pleistocene dune sands|
|Qmt||Pleistocene marine terrace deposits|
|Qoa||Early or middle Pleistocene undifferentiated alluvial deposits|
|br||Pre-Quaternary deposits and bedrock, undifferentiated|
|contact, certain||Observed contact|
|contact, approx. located||Contact whose position is not precisely known|
|contact, concealed||Concealed contact whose position is inferred|
|contact, inferred||Contact whose position is inferred|
|fault, certain||Observed fault|
|fault, approx. located||Fault whose position is not precisely known|
|fault, concealed||Concealed fault whose position is inferred|
|water boundary||Boundary of area of water|
|map boundary||Extent of mapped area|
|Ground Settlement||Pre-Loma Prieta Earthquake ground settlement|
|Ground Settlement 1989||Ground settlement during the Loma Prieta Earthquake|
|Lateral Spreading||Pre-Loma Prieta earthquake lateral spreading|
|Lateral spreading 1989||Lateral spreading during the Loma Prieta earthquake|
|Sand boils||Pre-Loma Prieta earthquake sand boil|
|Sand boils and/or sand intrusion||Sand boils and/or sand intrusion during the Loma Prieta earthquake|
|H2O||Area of water|
|vh||very high liquefactoin susceptibility|
|h||High liquefaction susceptibility|
|m||moderate liquefaction susceptibility|
|l||Low liquefaction susceptibility|
|vl||Very low to none liquefaction susceptibility|
Carl M. Wentworth, Todd T. Fitzgibbon, and Geoffrey A. Phelps graciously provided assistance with Alacarte and ARC/INFO. The scanning and editing of the digital maps was done by Scott E. Graham, Carolyn E. Randolph and Thomas E. May. Earl E. Brabb provided much helpful advice and feedback, as well as arranging for material support for the project.
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.
Are there legal restrictions on access or use of the data?
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
This database, identified as "Quaternary Geology and Liquefaction Susceptibility, San Francisco, California 1:100,000 Quadrangle: A digital database," has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.
|Data format:||Depositional contacts, faults, and unit labels, Liquefaction susceptibility, Historical liquefaction events, base maps in format ARCE (version 7.x) Size: 14|