High-Resolution Seismic-Reflection and Marine-Magnetic Data from Offshore Central California—San Gregorio to Point Sur
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Frequently anticipated questions:
- Title:
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High-Resolution Seismic-Reflection and Marine-Magnetic Data from Offshore Central California - San Gregorio to Point Sur
- Abstract:
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The U.S. Geological Survey collected high-resolution seismic-reflection data on four surveys (S-N1-09-MB, S-15-10-NC, S-06-11-MB, and S-04-12-MB) and marine-magnetic data on one survey (S-06-11-MB) between 2009 and 2012, offshore of central California between San Gregorio and Point Sur. This work was supported in part by the California Seafloor Mapping Program.
The survey areas span about 120 km of California's coast (including Monterey Bay). Most data were collected aboard the U.S. Geological Survey R/V Parke Snavely. Cumulatively, approximately 1,410 km of single-channel seismic-reflection data were acquired, mainly using a SIG 2mille minisparker. About 44 km of data were collected simultaneously using an EdgeTech Chirp 512. Subbottom acoustic penetration spanned tens to several hundreds of meters, variable by location. Marine magnetic data were collected on approximately 460 km of track lines (mainly in southern Monterey Bay) using a Geometrics G882 cesium-vapor marine magnetometer.
This report includes maps and navigation files of the surveyed transects, linked to Google Earthª software, as well as digital data files showing images of each transect in SEG-Y and JPEG formats. The images of bedrock, sediment deposits, and tectonic structure provide geologic information that is essential to hazard assessment, regional sediment management, and coastal and marine spatial planning at Federal, State and local levels, as well as to future research on the geomorphic, sedimentary, tectonic, and climatic record of central California.
- Supplemental_Information:
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The SIG 2mille minisparker system uses a 500-Joule, high-voltage electrical discharge fired at intervals ranging from 0.5 to 2.5 seconds depending on depth. The source signal frequency bandwidth is about 100 to 1600 Hz. One-half second intervals were used where water depth was less than about 350 m, which characterizes most of the study area. The 0.5 to second firing rate and normal survey speeds of 4 to 4.5 nautical miles per hour yield a data trace about every meter. The data were recorded on a 15-m-long hydrophone streamer in standard SEG-Y 32-bit floating point format with Triton Subbottom Logger (SBL) software that merges seismic-reflection data with differential GPS navigation data. After the survey, a short-window (20 ms) automatic gain control (AGC) algorithm and a 160 to 1,200 Hz bandpass filter were applied to the minisparker data to make the JPEG images in this report. The SEG-Y files have been resampled to 8 kHz. Data quality varies with substrate, with penetration up to 200 to 300 m in inferred fine-grained sediments.
The Edgetech 512 Chirp subbottom profiling system consists of a source transducer and an array of receiving hydrophones housed in a 500-lb "fish" towed at a depth of several meters below the sea surface. The swept-frequency "chirp" source signal is 500 Hz to 4,500 Hz, and data are recorded by hydrophones located on the bottom of the fish. After the survey, a short-window (20 ms) automatic gain control (AGC) algorithm was applied to these data to create the JPEG images. The SEG-Y files have been resampled to 8kHz. Data quality similarly varies with substrate, but penetration rarely exceeds a few tens of meters.
Marine-magnetic data were collected on survey S-06-11-MB using the Geometrics G882 cesium vapor magnetometer. The magnetometer was towed approximately 50 m behind the vessel. Magnetic data were collected at a 10 Hz sample rate along NE/SW transects, simultaneously with the mini-sparker seismic-reflection data, at a line spacing of 1,250 m. Magnetic and seismic-reflection data also were collected along a number of shore-parallel tie lines (see Survey Map). During the survey, a magnetic base station was set up onshore in Moss Landing at Moss Landing Marine Labs (lat 36.7948° N., long 121.7879° W.) to measure the local magnetic field continuously in order to remove diurnal field variations from the offshore survey. Base station readings were recorded every minute using a Geometrics G856 proton precession magnetometer.
Initial processing of the magnetic data involved smoothing, mainly to remove noise from the mini-sparker source. The data smoothing resulted in approximate along-track data point spacing of 10 m (boat speed 4 kts). Further processing included removal of the diurnal field variation by using the magnetic base-station readings and subtraction of the reference field defined by the International Geomagnetic Reference Field (IGRF) for 2011. The processed magnetic data are plotted in profile view above the seismic-reflection data. These images can be accessed from the Survey Map and Data Tables section of this report.
Additional information about the USGS field activity S-N1-09-MB is available at
<http://walrus.wr.usgs.gov/infobank/s/sn109mb/html/s-n1-09-mb.meta.html>.
Additional information about the USGS field activity S-16-10-NC is available at
<http://walrus.wr.usgs.gov/infobank/s/s1510nc/html/s-15-10-nc.meta.html>.
Additional information about the USGS field activity S-06-11-MB is available at
<http://walrus.wr.usgs.gov/infobank/s/s0611mb/html/s-06-11-mb.meta.html>.
Additional information about the USGS field activity S-04-12-MB is available at
<http://walrus.wr.usgs.gov/infobank/s/s0412mb/html/s-04-12-mb.meta.html>.
- How should this data set be cited?
Ray W. Sliter, Samuel Y. Johnson, Janet T. Watt, Daniel S. Scheirer, Parker Allwardt, and Peter J. Triezenberg, 2013, High-Resolution Seismic-Reflection and Marine-Magnetic Data from Offshore Central California - San Gregorio to Point Sur: U.S. Geological Survey Open-File Report 2013-1071, U.S. Geological Survey, Menlo Park, CA.
Online Links:
- What geographic area does the data set cover?
- West_Bounding_Coordinate: -122.4946
- East_Bounding_Coordinate: -121.7846
- North_Bounding_Coordinate: 37.5017
- South_Bounding_Coordinate: 36.3169
- What does it look like?
- <http://pubs.usgs.gov/of/2013/1071/tracklines/sparker2008/jpg/MBS-07.jpg> (JPEG)
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Example of single-channel mini-sparker seismic data accessible via this report.
- Does the data set describe conditions during a particular time period?
- Beginning_Date: 10-Nov-2009
- Ending_Date: 22-May-2012
- Currentness_Reference: ground condition
- What is the general form of this data set?
- Geospatial_Data_Presentation_Form: seismic reflection profile section
- How does the data set represent geographic features?
- How are geographic features stored in the data set?
- Indirect_Spatial_Reference:
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Horizontal X and Y locations for the seimic profiles location are provided in ASCII position files and are also stored in the SEG-Y data trace headers in the standard header locations.
- What coordinate system is used to represent geographic features?
- Grid_Coordinate_System_Name: Universal Transverse Mercator
- Universal_Transverse_Mercator:
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- UTM_Zone_Number: 10
- Transverse_Mercator:
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- Scale_Factor_at_Central_Meridian: 0.9996
- Longitude_of_Central_Meridian: -119.0
- Latitude_of_Projection_Origin: 0.0
- False_Easting: 500000
- False_Northing: 0
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 3
Ordinates (y-coordinates) are specified to the nearest 3
Planar coordinates are specified in seconds
The horizontal datum used is World Geodetic System 1984.
The ellipsoid used is WGS 84.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257.
- How does the data set describe geographic features?
- Entity_and_Attribute_Overview:
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Ascii data sets s-n1-09-mb.410_sparker, s-15-10-nc.410_sparker, s-06-11-mb.410_chirp, s-06-11-mb.410_sparker, s-04-12-mb.410_chirp, s-04-12-mb.410_sparker have initial header records followed by data records with these fields - 4-digit year, 3-digit day of year, 2-digit hour, 2-digit minute, 2-digit second, 1-digit tenth of second, decimal degree latitude, decimal degree longitude, alpha-numeric line ID, FFID number, Shot number, and CDP number. Example:
! 06/18/2012 ray s-04-12-mb.410_sparker
!
! merged segy times with raw nav June-2012
!
!
20121351615330 36.84835 -122.19637 OMBS-02 1 1 1
20121351616340 36.84877 -122.19474 OMBS-02 2 2 2
20121351616350 36.84878 -122.19472 OMBS-02 3 3 3
20121351616360 36.84880 -122.19469 OMBS-02 4 4 4
20121351616370 36.84881 -122.19467 OMBS-02 5 5 5
- Entity_and_Attribute_Detail_Citation:
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U.S. Geological Survey, USGS CMG InfoBank format for Seismic FFID/Shot/CDP data, 2012, <http://walrus.wr.usgs.gov/infobank/programs/html/dictionary2html/format_410.html>.
- Entity_and_Attribute_Overview:
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Ascii data set s-6-09-sc.mag.csv.zip, exported from Oasis montaj as a .csv file, has initial header records followed by data records with these fields - date yr/mo/day, day of June 2008 in Pacific Daylight Time, time hr:mn:sc, decimal degree latitude, decimal degree longitude, ship speed-knots, magnetometer signal level, raw magnetic data-nanotesla, magnetic data with IGRF correction-nanotesla, base station magnetic data-nanotesla, magnetic data with IGRF and base station correction-nanotesla, magnetic data with IGRF/base station/leveling correction-nanotesla. The data are separated by line number. Example:
/Date,Day_of_Jun2008_PDT_,Time,LatMag,LonMag,Speed_kts,SignalLevel,Mag_raw,Mag_IGRF,Basemag,Mag_corr_basemag,Mag_level
//Flight 0
//Date 2008/09/17
Line 0
2008/06/10,10.587384,14:05:50,35.2820680,-121.0099651,3.67,1605.4,47800.243,-174.0,-24.4,-149.7,-143.6
2008/06/10,10.587442,14:05:55,35.2821117,-121.0098761,4.57,1601.7,47800.509,-173.7,-24.4,-149.3,-143.2
2008/06/10,10.587500,14:06:00,35.2821745,-121.0097416,5.33,1617.0,47801.237,-173.1,-24.4,-148.7,-142.6
2008/06/10,10.587558,14:06:05,35.2822343,-121.0096140,5.38,1630.7,47800.939,-173.4,-24.4,-149.0,-142.9
2008/06/10,10.587616,14:06:10,35.2822985,-121.0094773,5.41,1633.6,47800.897,-173.5,-24.4,-149.1,-143.0
2008/06/10,10.587674,14:06:15,35.2823586,-121.0093479,5.32,1635.4,47802.066,-172.4,-24.5,-147.9,-141.8
- Entity_and_Attribute_Detail_Citation:
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Geosoft, Oasis montaj, 2012, <http://www.geosoft.com/pinfo/oasismontaj/index.asp>.
- Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
- Ray W. Sliter, Samuel Y. Johnson, Janet T. Watt, Daniel S. Scheirer, Parker Allwardt, and Peter J. Triezenberg
- Who also contributed to the data set?
U.S. Geological Survey
- To whom should users address questions about the data?
U.S. Geological Survey (USGS), Pacific Coastal and Marine Science Center (PCMSC)
Attn: Ray W. Sliter
Geophysicist
USGS, 400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
USA
(831) 460-7427 (voice)
(831) 460-7456 (FAX)
rsliter@usgs.gov
Between 2009 and 2012, the U.S. Geological Survey collected high-resolution seismic-reflection data on four surveys (S-N1-09-MB, S-15-10-NC, S-06-11-MB, and S-04-12-MB) and marine-magnetic data on one survey (S-06-11-MB), offshore of central California between San Gregorio and Point Sur (figure 1). The composite survey area spans about 120 km of the coast and includes all of California's State Waters, including Monterey Bay. The survey area includes the mouth and inner portion of Monterey submarine canyon and lies entirely within the Monterey Bay National Marine Sanctuary. Most data were collected aboard the U.S. Geological Survey R/V Parke Snavely. Cumulatively, approximately 1,410 km of seismic-reflection lines and 460 km of marine-magnetic profiles were acquired.
The study area has particular interest for environmental and geologic hazards considerations and has been the focus of significant recent oceanographic and geologic research (Eittreim and Noble, 2002). An understanding of the region's ecosystems and how they function is fundamental to effective stewardship of California's State Waters and the Monterey Bay National Marine Sanctuary (Eittreim and others, 2002). The need for accurate characterization of the seafloor and its substrate, including sediment distribution and thickness as revealed by high-resolution seismic-reflection data, is important for building such an understanding, particularly of the region's benthic ecosystem dynamics.
The study area is cut by active faults, most notably the San Gregorio Fault and the Monterey Bay Fault (Greene and others, 2002). The right-lateral San Gregorio Fault is one of the major strike-slip faults in the widely distributed transform plate boundary along the west coast of North America (Dickinson and others, 2005). This fault system extends along the California Coast for about 400 km from Point Arguello northward to Bolinas and has an estimated slip rate of 3 to 7 mm/yr (Wills and others, 2008). The Monterey Bay Fault either converges with or is truncated by the San Gregorio Fault in northern Monterey Bay. The high-resolution seismic-reflection and marine magnetic data collected in these surveys provide detailed information on shallow geologic structure and recent deformation that will be important in further understanding these faults and in improving earthquake hazard assessments.
Finally, these geophysical data will contribute to a range of geologic and habitat map products that will be used for a variety of coastal and marine spatial-planning applications.
- From what previous works were the data drawn?
- How were the data generated, processed, and modified?
- Date: 2012 (process 1 of 10)
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Refer to report sections "Data Acquisition and Processing" for details of geophysical data acquisition and processing sequence used for data in this report. - Ray W. Sliter
- Date: 2012 (process 2 of 10)
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Created bathymetry overlay using GMT <http://gmt.soest.hawaii.edu/>. - Peter J. Triezenberg
- Date: 2010 (process 3 of 10)
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Created interactive trackline map using Google Maps API <http://code.google.com/apis/maps/>. - Peter J. Triezenberg
- Date: 2010 (process 4 of 10)
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Created downloadable Google Earth "kmz" file <http://code.google.com/apis/kml/>. - Peter J. Triezenberg
- Date: 2012 (process 5 of 10)
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Created seismic profile images using Seismic Unix <http://www.cwp.mines.edu/cwpcodes/> to provide format options for downloading data. - Ray W. Sliter
Person who carried out this activity:
U.S. Geological Survey (USGS), Coastal and Marine Geology (CMG)
Attn: Ray W. Sliter
Geophysicist
USGS, 400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
USA
(831) 460-7427 (voice)
(831) 427-4709 (FAX)
rsliter@usgs.gov
- Date: 2012 (process 6 of 10)
-
Converted profiles to JPEG files using ImageMagick <http://www.imagemagick.org/>. - Peter J. Triezenberg
- Date: 2012 (process 7 of 10)
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Used GEODAS (GEOphysical DAta System) to create a custom bathymetric and topographic grid for the southern California region covered by the cruise maps. The website is: <http://www.ngdc.noaa.gov/mgg/geodas/geodas.html>. The parameters used are as follows: Grid Database: US Coastal Relief Model Grids Grid Area in degrees and minutes: 34:30 N to 33:48 N, 119:00 W to 120:24 W Grid Cell Size: 3 seconds Grid Format: XYZ (lon, lat, depth), no header, space-delimited, omit empty grid cells. Cell Parameters: 4-byte floating point, tenths of meters Land/Sea Coverage: Sea cells only. - Peter J. Triezenberg
Person who carried out this activity:
U.S. Geological Survey (USGS), Coastal and Marine Geology (CMG)
Attn: Peter J. Triezenberg
Geologist
USGS, 400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
USA
(831) 460-7413 (voice)
(831) 427-4709 (FAX)
ptriezenberg@usgs.gov
- Date: 2012 (process 8 of 10)
-
Processed raw magnetic data using GMT <http://gmt.soest.hawaii.edu/>. Also used several Unix utilities and some home-grown programs to convert the raw ship and base-station magnetic data into the corrected form for import into Oasis montaj. - Daniel S. Scheirer
Person who carried out this activity:
U.S. Geological Survey (USGS)
Attn: Janet T. Watt
USGS, 400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
USA
(831) 460-7565 (voice)
jwatt@usgs.gov
- Date: 2012 (process 9 of 10)
-
Performed magnetic survey leving using Oasis montaj <http://www.geosoft.com/pinfo/oasismontaj/index.asp>. - Janet T. Watt
- Date: 2012 (process 10 of 10)
-
Gridded preliminary magnetic data and exported TIFF files using Oasis montaj <http://www.geosoft.com/pinfo/oasismontaj/index.asp>. - Janet T. Watt
Person who carried out this activity:
U.S. Geological Survey (USGS)
Attn: Janet T. Watt
USGS, 400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
USA
(831) 460-7565 (voice)
jwatt@usgs.gov
- What similar or related data should the user be aware of?
U.S. Geological Survey (USGS), Coastal and Marine Geology (CMG), 2013, USGS CMG S-04-12-MB Metadata.
Online Links:
- How well have the observations been checked?
Data have not been independently verified.
- How accurate are the geographic locations?
Shot point numbers in the data files correspond to those in the navigation files. The horizontal positional accuracy of the seismic data thus linked to ship's position is estimated to be within 30 meters.
- How accurate are the heights or depths?
Depths shown in the seismic data files are in milliseconds (round trip travel time) and are referenced to sea level.
- Where are the gaps in the data? What is missing?
Reference the full report for a description of data coverage. All seismic-reflection data collected on the referenced cruises have been included in this report. Some seismic profiles have gaps in them due to system crashes, mammal shutdowns or hardware maintenance.
- How consistent are the relationships among the observations, including topology?
Undetermined
Are there legal restrictions on access or use of the data?
- Access_Constraints:
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Information presented in this publication is considered public information and may be distributed or copied.
- Use_Constraints:
-
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.
Some USGS information accessed through this means may be preliminary in nature and presented without the approval of the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the responsibility of the user.
- Who distributes the data set? (Distributor 1 of 1)
U.S. Geological Survey (USGS), Coastal and Marine Geology (CMG)
Attn: Ray W. Sliter
Geophysicist
USGS, 400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
USA
(831) 460-4727 (voice)
(831) 427-4709 (FAX)
rsliter@usgs.gov
- Contact_Instructions:
-
Data may be available off-line only by special arrangement with the distributor above. Please use the on-line download option unless precluded by download times or access difficulties.
- What's the catalog number I need to order this data set?
U.S. Geological Suvey Open-File Report 2013-1071
- What legal disclaimers am I supposed to read?
This information is not intended for navigational purposes.
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.
Reference herein to any specific commercial product, process, or service
by trade name, trademark, manufacturer, or otherwise does not constitute
or imply its endorsement, recommendation, or favoring by the United States
Government or any agency thereof.
Some USGS information accessed through this means may be preliminary in nature and presented without the approval of the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the responsibility of the user.
- How can I download or order the data?
- Availability in digital form:
- Cost to order the data: None
- What hardware or software do I need in order to use the data set?
Use of SEG-Y data requires specialized software, such as ProMax and Seisworks by Landmark Geophysical; FOCUS and SeisX by Paradigm Geophysical; SPW by Parallel Geoscience; or VISTA by Seismic Image Software.
- Dates:
- Last modified: 21-Mar-2013
- Metadata author:
-
U.S. Geological Survey (USGS), Coastal and Marine Geology (CMG)
Attn: Ray W. Sliter
Geophysicist
USGS, 400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
USA
(831) 460-7427 (voice)
(831) 427-4709 (FAX)
rsliter@usgs.gov
- Metadata standard:
- FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
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