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Open-File Report 95-597

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# Geologic Map of the Hayward fault zone, Contra Costa, Alameda, and Santa Clara Counties, California: A digital database

#### By R.W. Graymer, D.L. Jones, and E.E. Brabb

| Introduction
The Hayward is one of three major fault zones of the San Andreas system that haveproduced large historic earthquakes in the San Francisco Bay Area (the others being theSan Andreas and Calaveras). Severe earthquakes were generated by this fault zone in 1836and in 1868, and several large earthquakes have been recorded since 1868. The Haywardfault zone is considered to be the most probable source of a major earthquake in the SanFrancisco Bay Area, as much as 28% chance for a magnitude 7 earthquake before the year2021 (Working Group on California Earthquake Probabilities, 1990).

The Hayward fault zone, as described in this work, is a zone of highly deformed          rocks, trending north 30 degrees west and ranging in width from about 2 to 10 kilometers.          The historic earthquake generating activity has been concentrated in the western portion of          the zone, but the zone as a whole reflects deformation derived from oblique right-lateral and          compressive tectonic stress along a significant upper crustal discontinuity for the past 10          million or more years.

The Hayward fault zone is bounded on the east by a series of faults that demarcatethe beginning of one or more structural blocks containing rocks and structures unrelated tothe Hayward fault zone. The eastern bounding faults are, from the south, the Calaveras,Stonybrook, Palomares, Miller Creek, and Moraga faults. These faults are not consideredto be part of the Hayward fault zone, although they are shown on the map to demarcate itsboundary. The western boundary of the zone is less clearly defined, because the alluviumof the San Francisco Bay and Santa Clara Valley basins obscures bedrock and structuralrelationships. Although several of the westernmost faults in the zone clearly project underor through the alluvium, the western boundary of the fault is generally considered to be thewesternmost mapped fault, which corresponds more or less with the margin of thickunconsolidated surficial deposits. The Hayward fault zone is truncated to the south by theCalaveras fault, which trends about north 10 west, and so forms an oblique east and southboundary. All of the faults within the southern part of the zone probably splay into theCalaveras fault. The northern margin of the zone as dealt with herein is San Pablo Bay, butthe zone of deformation undoubtedly continues north of the Bay through the area boundedby the Rodgers Creek and Tolay faults. | First posted September 19, 2002

**Database file**s
- **Readme** TXT (9.5 kB)  Database explanation (README) pamphlet as an unformatted, text-only file 
- **Database** TAR.Z (18.6 MB)  Compressed tarfile containing the dataset in ARC/INFO 6.x coverage format 
- **Pamphlet** PDF (35 kB)  Database explanation pamphlet as a formatted PDF file 
- **Pamphlet** PS (138 kB)  Database explanation pamphlet as a formatted PostScript plot file 

**Geologic explanation pamphlet**
- **Geo Pamphlet** PDF (46 kB)    Geologic explanation pamphlet as a formatted PDF file 
- **Geo Pamphlet** TXT (51 kB)    Geologic explanation pamphlet as an unformatted, text-only file 
- **Geo Pamphlet** PS (238 kB)    Geologic explanation pamphlet as a formatted PostScript plot file 

**Geologic Maps**
- **Geologic map north half** PDF (3.4 MB)  Northern geologic map sheet as a PDF file 
- **Geologic map south half** PDF (2.9 MB)  Southern geologic map sheet as a PDF file 
- **Geologic map sheet** JPG (340 kB)  Geologic map sheet as a JPEG file (base-map removed) 
- **Explanation sheet** PDF (3.8 MB)
- **Geologic map files** TAR.Z (10.7 MB)  Compressed tar file containing three Postscript plottable files of images of the geologic map at a scale of 1:50,000 and index map at a scale of 1:100,000 

**For additional information, contact:**          Geology, Minerals, Energy, and Geophysics Science CenterU.S. Geological Survey345 Middlefield Road, MS 901Menlo Park, CA 94025-3591http://geomaps.wr.usgs.gov/gmeg/

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### Suggested citation:

Graymer, R. W., Jones, David Lawrence, Brabb, Earl E., 1995, Geologic Map of the Hayward fault zone, Contra Costa, Alameda, and Santa Clara Counties, California: A digital database: U. S. Geological Survey Open-File Report 95-597, 8 pp., *https://pubs.usgs.gov/of/1995/of95-597/*.

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U.S. Department of the Interior |            U.S. Geological Survey           	URL: *http://pubsdata.usgs.gov/pubs/of/1995/of95-597/index.html*            Page Contact Information: GS Pubs Web Contact           	Page Last Modified: Wednesday, 07-Dec-2016 15:59:08 EST