Field activity B-04-12-NC: Magnetic-field level data collected between Punta Gorda and Fort Bragg (northern California) from 09/17/2012 to 09/25/2012

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Frequently anticipated questions:

What does this data set describe?

Title:
Field activity B-04-12-NC: Magnetic-field level data collected between Punta Gorda and Fort Bragg (northern California) from 09/17/2012 to 09/25/2012
Abstract:
This dataset includes Magnetic-field level data jointly collected by the U.S. Geological Survey (USGS) and Oregon State University in 2012, between Punta Gorda and Fort Bragg in northern California.
Supplemental_Information:
Additional information about the field activity from which these data were derived is available online at:
https://cmgds.marine.usgs.gov/fan_info.php?fan=B0412NC
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  1. How might this data set be cited?
    Beeson, Jeffrey W., Johnson, Samuel Y., Goldfinger, Chris, and Hartwell, Stephen R., 20160606, Field activity B-04-12-NC: Magnetic-field level data collected between Punta Gorda and Fort Bragg (northern California) from 09/17/2012 to 09/25/2012: data release DOI:10.5066/F7GT5K8R, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    This is part of the following larger work.

    Beeson, Jeffrey W., Johnson, Samuel Y., Goldfinger, Chris, and Hartwell, Stephen R., 2016, Marine geophysical data—Cape Mendocino to Point Arena, northern California: data release DOI:10.5066/F7GT5K8R, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA.

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -124.47752
    East_Bounding_Coordinate: -123.78899
    North_Bounding_Coordinate: 40.30684
    South_Bounding_Coordinate: 39.35035
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 17-Sep-2012
    Ending_Date: 25-Sep-2012
    Currentness_Reference:
    ground condition at the time the data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: comma-delimited text
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Point
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.00001. Longitudes are given to the nearest 0.00001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.
      Vertical_Coordinate_System_Definition:
      Depth_System_Definition:
      Depth_Datum_Name: Local surface
      Depth_Resolution: 0.1
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Attribute values
  7. How does the data set describe geographic features?
    B-04-12-NC_Magnitic
    Points representing magnetic anomaly level (Source: This report)
    Line
    Survey line identifier (Source: This report) Each line contained in the survey has a unique identifier
    Date
    Date of data point collection (Source: This report) The date the data point was collected
    Time
    Time of data point collection (Source: This report) The time the data point was collected
    lon_n83
    Longitute of data point (Source: This report) Longitude of data point in world coordinates
    lat_n83
    Longitute of data point (Source: This report) Latitude of data point in world coordinates
    x_n83
    X coordinate of data point (Source: This report) Longitude of data point in NAD83 UTM zone 10N
    y_n83
    Y coordinate of data point (Source: This report) Latitude of data point in NAD83 UTM zone 10N
    G882_raw
    Raw Magnetic level (Source: This report) Unprocessed magnetic level at data point
    G882_DIURNAL
    Magnetic level correction applied (Source: This report) Magnetic level correction applied (see: Precess_Step 4)
    G882_IGRF
    Magnetic level with International Geomagnetic Reference Field (IGRF) correction applied (Source: This report) Magnetic level with International Geomagnetic Reference Field (IGRF) correction applied
    FRN_base
    International Geomagnetic Reference Field at Fresno base (Source: This report) Value of International Geomagnetic Reference Field at the Fresno Base at the time data point was collected
    total_field_anom
    Calculated Total Field (Residual) Anomaly (Source: This report) Magnetic level correction applied (see: Precess_Step 6)
    maglev_final
    Magnetic level Final (Source: This report) Magnetic level with directional correction applied (see: Precess_Step 6)

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Jeffrey W. Beeson
    • Samuel Y. Johnson
    • Chris Goldfinger
    • Stephen R. Hartwell
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Attn: PCMSC Science Data Coordinator
    2885 Mission Street
    Santa Cruz, CA

    831-427-4747 (voice)
    pcmsc_data@usgs.gov

Why was the data set created?

These data were collected as part of USGS efforts to better understand the northernmost section of the San Andreas Fault Zone. These data and information are intended for science researchers, students from elementary through college, policy makers, and general public.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 27-Jun-2013 (process 1 of 4)
    Magnetic data were postprocessed following the methodology of Nick Valleau at Geosoft. See http://www.geosoft.com/media/uploads/resources/technical-notes/microleveling%20tech%20note.pdf 1)Initial Processing in MagMap2000 -Download base files from INTERMAGNET observatory (http://www.intermagnet.org/apps/dl_data_prel_e.php) -Despike base files and visually inspect for dropouts -Apply bias to DIURNAL (base) readings for GMT to local PDT + longitude diff. from base to survey = 7hrs + 0.22hrs =-24,408sec **NOTE: 0.0666667hr/deg longitude correction -Import .survey files, despike 2)Import to Oasis -Remove periodic sparker spike from raw G882 and G882_diurnal channel using a non-linear filter GX = nlfilt (ex. filter width = 3 data points, filter tolerance = 0.3 nt) 3)Calculated IGRF for G882 data 4)Back calculated Base Magnetometer measurements G882filt-DIURNAL_filt = Fresno_base 5)Calculated IGRF value at base station FRN = 48909.6nT 6)Calculated Total Field (Residual) Anomaly using the following equation: A(x) = [F(x,t) - I(x)] - [FB(t) - IB] where: A(x)is total field anomaly at position x F(x,t) is the G882 reading at time t and position x I(x) is IGRF/DGRF at the G882 FB(t) is the base station reading at time t IB is the IGRF/DGRF at the base station Applying a decorrugation filter "R" and "P" lines only (500m line spacing, line azimuth=44 degrees) Following methodology of Nick Valleau at Geosoft - http://www.geosoft.com/media/uploads/resources/technical-notes/microleveling%20tech%20note.pdf FILTER PARAMETERS for "R" lines Butterworth filter: cutoff wavelength = 2000 (4 x line spacing) filter order = 8 (suggested) high-pass Directional Cosine filter: centre direction = 44 (flight line azimuth) degree of cosine function = 1 (suggested) pass (i.e., pass the features in the specified direction) NOTE: Can't apply low-pass filter to data in Nick's process b/c the cutoff wavelength is calculated using fiducials, which are dependent on boat speed, which is not constant (ex. boat goes faster while only collecting fill-in mag). So, maglev channels are simply sampled from the decor grid. FILTER PARAMETERS for "P" lines Butterworth filter: cutoff wavelength = 2000 (4 x line spacing) filter order = 8 (suggested) high-pass Directional Cosine filter: centre direction = 14 (flight line azimuth) degree of cosine function = 0.5 (suggested) pass (i.e., pass the features in the specified direction) Final processed data in column "maglev_final" Person who carried out this activity:
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Attn: Janet Watt
    Geologist
    2885 Mission Street
    Santa Cruz, CA
    US

    831-460-7565 (voice)
    831-427-4748 (FAX)
    jwatt@usgs.gov
    Date: 19-Oct-2020 (process 2 of 4)
    Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
    Date: 13-Oct-2021 (process 3 of 4)
    Edited metadata to correct minor typos and bring it up to PCMSC standards. No data were changed. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Susan Cochran
    Geologist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7545 (voice)
    scochran@usgs.gov
    Date: 24-Mar-2026 (process 4 of 4)
    The metadata title was modified to move the USGS field activity number to the beginning of the title. This was done to meet new system requirements as ScienceBase is migrated to a new platform, and to keep datasets grouped by field activity on the new data release landing page. (20260324). Person who carried out this activity:
    Manda Au
    U.S. Geological Survey
    Data Management Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7575 (voice)
    mau@usgs.gov
  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?
    Identified as best available version.
  2. How accurate are the geographic locations?
    Unspecified
  3. How accurate are the heights or depths?
    Unspecified
  4. Where are the gaps in the data? What is missing?
    Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    No formal logical accuracy tests were conducted

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints None. USGS-authored or -produced data and information are in the public domain.
Use_Constraints The U.S. Geological Survey requests to be acknowledged as the originator of the data in future products or derivative research. Share data products developed using these data with the U.S. Geological Survey.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO
    USA

    1-888-275-8747 (voice)
  2. What's the catalog number I need to order this data set? Downloadable magnetic field data
  3. What legal disclaimers am I supposed to read?
    These data, identified as magnetic field anomaly data, have been approved for release and publication by the U.S. Geological Survey (USGS). Although these data have been subjected to rigorous review and are 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 these data have been processed successfully on a computer system at the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 24-Mar-2026
Metadata author:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Attn: PCMSC Science Data Coordinator
2885 Mission Street
Santa Cruz, CA

831-427-4747 (voice)
pcmsc_data@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/DataReleases/ScienceBase/DR_F7GT5K8R/B-04-12-NC_Magnetic_metadata.faq.html>
Generated by mp version 2.9.51 on Fri Apr 10 16:37:27 2026