Computed tomography (CT) scans of percussion driven gravity cores collected in Alaskan lakes and fjords following the 2018 Anchorage earthquake

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Frequently anticipated questions:

What does this data set describe?

Title:
Computed tomography (CT) scans of percussion driven gravity cores collected in Alaskan lakes and fjords following the 2018 Anchorage earthquake
Abstract:
This dataset includes computed tomography (CT) scans of sediment cores collected from lacustrine and fjord basins in southcentral Alaska following the 2018 Anchorage earthquake. The cores were collected with a percussion driven gravity corer for use in regional hazard assessments relating to Alaska’s seismic hazard.
Supplemental_Information:
Additional information about the field activities from which these data were derived is available online at:
https://cmgds.marine.usgs.gov/fan_info.php?fan=2021-612-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2020-615-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2020-625-FA
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?
    Singleton, Drake M., Brothers, Daniel S., Hill, Jenna C., Haeussler, Peter J., and Witter, Robert C., 20230706, Computed tomography (CT) scans of percussion driven gravity cores collected in Alaskan lakes and fjords following the 2018 Anchorage earthquake: data release DOI:10.5066/P924775B, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    This is part of the following larger work.

    Singleton, Drake M., Brothers, Daniel S., Hill, Jenna C., Haeussler, Peter J., and Witter, Robert C., 2023, Geophysical and core sample data collected in lakes and fjords of southcentral Alaska following the 2018 Anchorage earthquake: data release DOI:10.5066/P924775B, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA.

    Online Links:

    Other_Citation_Details:
    Suggested Citation: Singleton, D.M., Brothers, D.S., Hill, J.C., Haeussler, P.J., and Witter, R.C., 2023, Geophysical and core sample data collected in lakes and fjords of southcentral Alaska following the 2018 Anchorage earthquake: U.S. Geological Survey data release, https://doi.org/10.5066/P924775B.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -151.490850
    East_Bounding_Coordinate: -148.537050
    North_Bounding_Coordinate: 62.520180
    South_Bounding_Coordinate: 60.071108
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 08-Aug-2020
    Ending_Date: 22-Jun-2021
    Currentness_Reference:
    Ground conditions at time data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: JPG format images
  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 (108)
    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 WGS 1984.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257224.
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    Zip folder of CT scans of sediment cores. Images are in JPG format and include scans for both XZ and YZ directional slices. Naming convention for each core is: Field-Activity_Core-ID_[LASR]_[XZ or YZ slice]_R.jpg. Location information for each sediment core can be found in the 2021_612_2020_625_2020_615_core_nav shapefile included in this data release.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Drake M. Singleton
    • Daniel S. Brothers
    • Jenna C. Hill
    • Peter J. Haeussler
    • Robert C. Witter
  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?

Identification of fault-related submarine hazards is a primary mission of the USGS Coastal and Marine Hazards and Resources Program. Intraslab earthquakes, which occur at depth within the subducting plate, can cause intense shaking at the Earth’s surface, but do not cause surficial faulting or result in significant land level changes. The seismic shaking associated with intraslab earthquakes can remobilize subaqueous sediment and lead to gravity driven sediment flows, potentially creating a record of past shaking from these events. To gain a better understanding of the conditions that produce seismically triggered deposits in subaqueous basins the USGS collected Chirp seismic and sediment cores from several lakes and fjords following the M7.1 2018 Anchorage earthquake. These data are intended to further our understand of geologic hazard in southcentral Alaska, improve risk assessments for local communities and critical infrastructure, and to provide data for future research on regional paleoseismic records in southcentral Alaska.

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: 01-Nov-2020 (process 1 of 3)
    For field activities 2020-625-FA and 2020-615-FA sediment cores were collected via a percussion driven gravity corer from a variety of research vessels. The cores were transported back to the USGS Pacific Coastal and Marine Science Center core lab for subsequent analyses. Cores over 1.5 m in length were split into multiple sections to permit scanning in a Geotek RXCT X-ray tomography system. Two representative sections in each core along the XZ and YZ axes were output from the full 3D CT volumes. Images from the CT scanner had ruler scales appended using the Geotek Add Ruler v 1.4 software.
    Date: 01-Feb-2021 (process 2 of 3)
    For CT scans of cores collected during field activities 2020-625-FA and 2020-615-FA a signal reduction algorithm, needed to address oversaturation of original scans, was applied via Geotek LASR software. Output files have LASR designation appended to file name.
    Date: 01-Aug-2021 (process 3 of 3)
    For field activity 2021-612-FA sediment cores were collected via a percussion driven gravity corer from a converted cataraft. The cores were transported back to the USGS Pacific Coastal and Marine Science Center core lab for subsequent analyses. Cores over 1.5 m in length were split into multiple sections to permit scanning in a Geotek RXCT X-ray tomography system. Two representative sections in each core along the XZ and YZ axes were output from the full 3D CT volumes. Images from the CT scanner had ruler scales appended using the Geotek Add Ruler v 1.4 software.
  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?
    Quality control of attribute accuracy was conducted during field data collection and processing workflows.
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Dataset will be updated to include additional CT-scans collected during these field activities as those cores are processed through the sediment core lab at the Pacific Coastal and Marine Science Center. 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?
    The ruler alongside the TIFF images are not corrected for sediment compaction and are relative to the beginning of the CT-scanner core track.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints None
Use_Constraints USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - CMGDS
    2885 Mission Street
    Santa Cruz, CA

    831-427-4747 (voice)
    pcmsc_data@usgs.gov
  2. What's the catalog number I need to order this data set? Core CT images are provided in a zip archive (2021-612_2020-625_2020-615_core_CT_Images.zip) accompanied by CSDGM FGDC-compliant metadata. Note that rulers appended to images are provided for scale only and do not necessarily correlate with length measurements in the tabular data provided with this data release (for example the length along a core where a radiocarbon sample was collected). Users are advised to use the rulers as a scale to make length measurements along the core. Full 3D CT scan volumes are available upon request; please contact the PCMSC Data Coordinator about availability.
  3. What legal disclaimers am I supposed to read?
    Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by 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.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: Zip file contains CT scans of each core in JPG format. in format JPEG (version NA) Size: 283.6
      Network links: https://doi.org/10.5066/P924775B
    • Cost to order the data: None.

  5. What hardware or software do I need in order to use the data set?
    Core photographs can be viewed with any standard image software.

Who wrote the metadata?

Dates:
Last modified: 06-Jul-2023
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/CMGDS_DR_tool/DR_P924775B/2021-612_2020-625_2020-615_core_CT_Images_metadata_052223.05-22-2023.faq.html>
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