Faults--Offshore of Half Moon Bay Map Area, California

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What does this data set describe?

Title: Faults--Offshore of Half Moon Bay Map Area, California
This part of DS 781 presents data for faults for the geologic and geomorphic map of the Offshore of Half Moon Bay map area, California. The vector data file is included in "Faults_OffshoreHalfMoonBay.zip," which is accessible from <https://pubs.usgs.gov/ds/781/OffshoreHalfMoonBay/data_catalog_OffshoreHalfMoonBay.html>.

The Offshore of Half Moon Bay map area lies about 12 km southwest of the San Andreas Fault, the dominant structure in the distributed, right-lateral, transform boundary between the North American and Pacific plates. The map area straddles the right-lateral San Gregorio Fault, the most important structure west of the San Andreas Fault in this broad zone. The San Gregorio is part of fault system that occurs predominantly in the offshore, extending about 400 km from Point Conception on the south to Bolinas and Point Reyes on the north (Dickinson and others, 2005), intersecting land at a few coastal promontories. In the Offshore of Half Moon Bay map area, the San Gregorio Fault forms a distributed shear zone about 2 to 4.5 km wide that includes two primary diverging fault strands. The eastern strand (also known as the Seal Cove Fault or Coastways Fault) roughly parallels the shoreline, lies onshore for about 3 km at Pillar Point, and locally forms the boundary between outcrops of Cretaceous grantic rocks to the east and Purisima Formation to the west. The western strand (also known as the Frijoles Fault) lies entirely offshore and forms a boundary between the Purisima Formation on the east and undifferentiated Cretaceous and (or) Tertiary rocks (Pigeon Point Formation?) of the Pigeon Point structural block (McCulloch, 1987) on the west. The Pigeon Point block forms a northwest-trending bedrock ridge that extends offshore for about 30 km from Pescadero Point and forms the northwest boundary of the outer Santa Cruz Basin (McCulloch, 1987).

Cumulative lateral slip on the San Gregorio Fault zone is thought to range from 4 to 10 mm/yr in this region (U.S. Geological Survey, 2010). Bathymetric (Bathymetry--Offshore Half Moon Bay, California, DS 781) and seismic-reflection data (see field activity S-15-10-NC) reveal that the offshore outcrops of the Purisima Formation between the eastern and western strands of the San Gregorio Fault Zone are spectacularly folded, faulted and rotated by the strike-slip motion and drag along the faults. The entire map area lies along strike with the young, high topography of the Santa Cruz Mountains and Coast Ranges. This regional uplift has been linked to a northwest transpressive bend in the San Andreas Fault (for example, Zoback and others, 1999). Uplift of nearby marine terraces at rates up to 0.44 mm/yr confirms that this uplift includes the coastal zone (Weber and others, 1995).

Faults were primarily mapped by interpretation of seismic reflection profile data (see field activity S-15-10-NC). The seismic reflection profiles were collected between 2007 and 2010.

References Cited

Dickinson, W.R., Ducea, M., Rosenberg, L.I., Greene, H.G., Graham, S.A., Clark, J.C., Weber, G.E., Kidder, S., Ernst, W.G., and Brabb, E.E., 2005, Net dextral slip, Neogene San Gregorio-Hosgri fault zone, coastal California: Geologic evidence and tectonic implications: Geological Society of America Special Paper 391, 43 p.

McCulloch, D.S., 1987, Regional geology and hydrocarbon potential of offshore Central California, in Scholl, D.W., Grantz, A., and Vedder, J.G., eds., Geology and resource potential of the continental margin of Western North America and adjacent ocean basins - Beaufort Sea to Baja California: Circum-Pacific Council for Energy and Mineral Resources Earth Science Series, v. 6, p. 353-401.

U.S. Geological Survey and California Geological Survey, 2010, Quaternary fault and fold database for the United States, accessed April 5, 2012, from USGS website: <http://earthquake.usgs.gov/hazards/qfaults/>.

Weber, G.E., Nolan, J.M., and Zinn, E.N., 1995, Determination of late Pleistocene-Holocene slip rates along the San Gregorio fault zone, San Mateo and Santa Cruz counties, California: Final Technical Report, National Earthquake Hazard Reduction Program, Contract No. 1434-93-G-2336, 70 p., 4 map sheets.

Zoback, M.L., Jachens, R.C., and Olson, J.A., 1999, Abrupt along-strike change in tectonic style: San Andreas fault zone, San Francisco Peninsula: Journal of Geophysical Research, v. 104 (B5), p. 10,719-10,742.

Map political location: San Mateo County, California Compilation scale: 1:24,000 Base maps used are hillshades generated from IfSAR, LiDAR, and multibeam mapping both onshore and offshore (see see Bathymetry--Offshore Half Moon Bay, California, DS 781, for more information).
  1. How should this data set be cited?

    Greene, H.G., Manson, M.W., Dieter, B.E., Ross, S.L., Hartwell, S.R., Johnson, S.Y., and Watt, J.T., 2014, Faults--Offshore of Half Moon Bay Map Area, California:.

    This is part of the following larger work.

    Cochrane, Guy R., Dartnell, Peter, Greene, H. Gary, Johnson, Samuel Y., Golden, Nadine E., Hartwell, Stephen R., Dieter, Brian E., Mansion, Michael W., Sliter, Ray W., Ross, Stephanie L., Watt, Janet T., Endris, Charles A., Kvitek, Rikk G., Edwards, Brian D., Phillips, Eleyne L., Erdey, Mercedes D., Bretz, Carrie K., Chin, John L., and Bretz, Carrie K., 2014, California State Waters Map Series--Offshore of Half Moon Bay map area, California: Open-File Report OFR 2014-1214, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -122.56
    East_Bounding_Coordinate: -122.42
    North_Bounding_Coordinate: 37.55
    South_Bounding_Coordinate: 37.39

  3. What does it look like?

    <https://pubs.usgs.gov/ds/781/OffshoreHalfMoonBay/images/Faults_OffshoreHalfMoonBay.jpg> (JPEG)
    Faults offshore Half Moon Bay.

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 2007
    Ending_Date: 2010
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: vector digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):

      • String (46)

    2. What coordinate system is used to represent geographic features?

      The map projection used is WGS 1984 UTM Zone 10N.

      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.001
      Ordinates (y-coordinates) are specified to the nearest 0.001
      Planar coordinates are specified in Meter

      The horizontal datum used is D WGS 1984.
      The ellipsoid used is WGS 1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.

  7. How does the data set describe geographic features?

    lines representing mapped faults (Source: This report)

    Internal feature number. (Source: ESRI)

    Sequential unique whole numbers that are automatically generated.

    Feature geometry. (Source: ESRI)

    Coordinates defining the features.

    feature label (Source: This report)

    text field containing feature names if they are named

    Representation rule identifier (Source: This report)

    This field contains the representation rule in the ArcGIS file geodatabase that applied dashed or solid lines to faults. The line is dashed if faults are mapped in sediment and solid if they are mapped over rock or a visible scarp.

    Length of feature in internal units. (Source: ESRI)

    Positive real numbers that are automatically generated.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    USGS Pacific Coastal and Marine Science Center
    Attn: Stephen Hartwell
    400 Natural Bridges Drive
    Santa Cruz, CA 95060

    (831) 460-7814 (voice)
    (831) 427-4748 (FAX)

Why was the data set created?

To expand geologic mapping to the seafloor within the California's State Waters, to update coastal geologic mapping, and to contribute to a uniform regional geologic database, which can be used geographic information systems. Additionally, to provide a geologic map for the public and geoscience community to aid in assessments and mitigation of geologic hazards in the San Gregorio coastal region and to provide sufficient geologic information for land-use and land-management decisions both onshore and offshore. This information is not intended for navigational purposes.

How was the data set created?

  1. From what previous works were the data drawn?

    S-15-10-NC (source 1 of 2)
    U.S. Geological Survey (USGS) , Coastal and Marine Geology Program (CMGP), 2013, Seismic-reflection data acquisition data of field activity S-15-10-NC in offshore Pescadero from 08/02/2010 to 08/04/2010: U.S. Geological Survey (USGS) , Coastal and Marine Geology (CMG), Menlo Park, CA.

    Online Links:

    Type_of_Source_Media: ASCII lat/long shot point files
    Digital seismic data used to interpret subsurface geologic structure

    F-2-07-NC (source 2 of 2)
    U.S. Geological Survey (USGS) , Coastal and Marine Geology Program (CMGP), 2013, Geophysical data of field activity F-2-07-NC in Ano Nuevo to San Francisco from 03/22/2007 to 04/06/2007: U.S. Geological Survey (USGS) , Coastal and Marine Geology (CMG), Menlo Park, CA.

    Online Links:

    Type_of_Source_Media: ASCII lat/long shot point files
    Digital seismic data used to interpret subsurface geologic structure

  2. How were the data generated, processed, and modified?

    Date: 2011 (process 1 of 2)
    Faults were mapped onto shot lines based on the latitude and longitude of seismic picks from field activity S-15-10-NC.

    Date: 2011 (process 2 of 2)
    Faults were mapped onto shot lines based on the latitude and longitude of seismic picks from field activity F-2-07-NC.

  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

    Faults were primarily mapped by interpretation of seismic reflection profile data (see S-15-10-NC).
    Faults lines were digitized by heads-up screen digitization on to shot-point picks from seismic-line navigation data - each shot point has an associated lat/long in the survey data. Error is introduced from layback, as well as from interpretation of oblique features, so horizontal accuracy of fault and fold location is estimated to be on the order of 10 to 20 meters.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    Data are complete: no offshore features that could be accurately identified and represented at the compilation scale of 1:24,000 were eliminated or generalized. The smallest area represented is approximately 100 square meters. All geospatial database elements are attributed.

  5. How consistent are the relationships among the observations, including topology?

    Map elements were visually checked for overshoots, undershoots, duplicate features, and other errors by the lead authors and by the GIS technician(s) who created the digital database. Review drafts of the map were reviewed internally by at least two other geologists for consistency with basic geologic principles and general conformity to USGS mapping standards.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

If physical samples or materials are available, constraints on their on-site access are described in "WR CMG Sample Distribution Policy" at URL: <http://walrus.wr.usgs.gov/infobank/programs/html/main/sample-dist-policy.html>
This information is not intended for navigational purposes.
Read and fully comprehend the metadata prior to data use. Uses of these data should not violate the spatial resolution of the data. Where these data are used in combination with other data of different resolution, the resolution of the combined output will be limited by the lowest resolution of all the data.
Acknowledge the U.S. Geological Survey in products derived from these data. Share data products developed using these data with the U.S. Geological Survey.
This 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.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document these data in nonproprietary form, as well as in ArcInfo format, this metadata file may include some ArcInfo-specific terminology.

Who wrote the metadata?

Last modified: 2013
Last Reviewed: 25-Aug-2014
Metadata author:
U.S. Geological Survey, Coastal and Marine Geology Program
Attn: Stephen R. Hartwell
400 Natural Bridges Drive
Santa Cruz, CA 95060-5792

831-460-7814 (voice)
831-427-4748 (FAX)

Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

Generated by mp version 2.9.16 on Wed Jan 21 17:04:35 2015