GRAVITY DATA OF NEVADA
By
D.A. Ponce
1997

U.S. Geological Survey
345 Middlefield Rd. MS 989
Menlo Park, CA 94025
E-mail: ponce@usgs.gov
www site: http://pubs.usgs.gov/dds/dds-42/

U.S. GEOLOGICAL SURVEY DIGITAL DATA SERIES DDS-42

U.S. DEPARTMENT OF THE INTERIOR
Bruce Babbitt, Secretary

U.S. GEOLOGICAL SURVEY
Gordon P. Eaton, Director

For sale by
USGS Information Services
Box 25286, Building 810
Denver Federal Center
Denver, CO 80225
(303) 202-4200

Library of Congress Cataloging-in-Publications Data

Ponce, David A.

Gravity data of Nevada [computer file] / by D.A. Ponce

1 computer laser optical disc : col. ; 4 3/4 in. -- (U.S. Geological Survey digital data series : DDS-42) Computer data.

Title from disc label.

Audience: Geoscientists

1. Gravity anomalies--Nevada--Measurement.

2. Gravity anomalies--Southwestern States--Measurement.

I. National Geophysical Data Center.

II. Geological Survey (U.S.).

III. Series: U.S. Geological Survey digital data series:

DDS-42. QB337.5 <1997 00001> 526--DC12a 97-4516 CIP

CONTENTS

Abstract
Introduction
Acknowledgments
Disclaimer
System Requirements
Portable Document Format (PDF) File
Related World Wide Web Sites
Gravity Data Format and Reduction
Selected References
Appendix--List of Sources for Data from the National Geophysical Data Center

ILLUSTRATIONS

Figure 1. Index map showing 1 x 2 degrees quadrangles
Figure 2. Gravity station location map
Figure 3. Topographic map
Figure 4. Complete Bouguer gravity map
Figure 5. Isostatic gravity map

TABLES

Table 1. Data files on CD-ROM
Table 2. Format of gravity data
Table 3. Explanation of 4-digit accuracy code

ABSTRACT

Gravity data for the entire state of Nevada and adjacent parts of California, Utah, and Arizona are available on CD-ROM. About 80,000 gravity stations were compiled primarily from the National Geophysical Data Center and the U.S. Geological Survey. Gravity data were reduced to the Geodetic Reference System of 1967 and adjusted to the International Gravity Standardization Net 1971 gravity datum. Data were processed to complete Bouguer and isostatic gravity anomalies by applying standard gravity corrections including terrain corrections and isostatic corrections. A 1_README.TXT file describes the contents of the CD-ROM and includes a description of the data reduction process, selected principal fact references, and a list of sources for data from the National Geophysical Data Center.

INTRODUCTION

Gravity data for the entire state of Nevada and adjacent parts of California, Utah, and Arizona are available on Compact Disc-Read Only Memory (CD-ROM). Data are organized into 19 files, one for each of the 18 1 X 2 degree quadrangles (fig. 1) that cover Nevada as well as a single file containing all the data (table 1). About 80,000 gravity stations (fig. 2) have been compiled from various sources including the National Geophysical Data Center (National Geophysical Data Center, 1988), U.S. Geological Survey (USGS), Nevada Bureau of Mines and Geology, California Division of Mines and Geology, University of Nevada at Reno, Stanford University, Northwestern University, Colorado School of Mines, Los Alamos National Laboratory, and University of Texas at Dallas. Data were processed to complete Bouguer and isostatic gravity anomalies by applying standard gravity corrections including terrain corrections to a radial distance of 167 km and isostatic corrections based on an Airy-Heiskanen model of local compensation (Heiskanen and Moritz, 1967).

ACKNOWLEDGMENTS

I would especially like to thank Donald Plouff of the USGS for recent recompilations of several quadrangles in the northwestern part of Nevada and J.W. Erwin of the Nevada Bureau of Mines and Geology for access to various data sets throughout Nevada and for supporting a cooperative effort to release gravity data and maps for Nevada. Michael Diggles of the USGS developed the final CD-ROM architecture and produced the master. In addition, I acknowledge the contributions of numerous personnel from various organizations for acquiring or providing gravity data including:

G.A. Abrams, R.V. Allen, T.V. Bare, R.G. Bates, D.L. Berger, H.R. Blank, Jr., A.J. Bol, R.E. Bracken, B.R. Buchanan, S.F. Carle, J.E. Carlson, R.H. Chapman, L.L. Chau, B.A. Chuchel, A.H. Cogbill, Jr., A. Conradi, Jr., C.E. Corry, R.A. Crewdson, F.E. Currey, D.A. Dansereau, K.J. Danti, D.A. Dinter, T.J. Durbin, R.K. Edquist, C.F. Erdman, G.R. Erickson, D.G. Evans, E.A. Frick, J.D. Garing, M.L. Gerdes, J.F. Gibbs, J.I. Gimlett, J.M. Glen, R.H. Godson, V.J.S. Grauch, R.N. Harris, J. Hasbrouck, D.L. Healey, D.C. Hobach, K.D. Holden, R.C. Jachens, P.E. Jansma, D.R. Jefferris, M.F. Kane, C.R. Karish, A.M. Katzenstien, H.E. Kaufmann, D.R. Kietzman, J.D. Kibler, K.S. Kirchoff- Stein, N.E. Kitchen, S.B. Kohrn, S.C. Kuehn, V.E. Langenheim, J.H. Laudon, J.S. Lewis, R.B. Livermore, D.R. Mabey, J. Mariano, D.K. Maurer, C.H. Miller, E.G. Miller, M.E. Milling, R.L. Morin, C.K. Moss, H.W. Oliver, D.L. Peterson, R.W. Plume, W.L. Rambo, D. Reidy, S.L. Robbins, C.W. Roberts, J.R Rosenbaum, H.F. Ryan, J.J. Rytuba, R.W. Saltus, C.H. Sandberg, D.H. Schaefer, H.L. Scheirer, K.M. Schmidt, E.D. Seals, L. Senior, D. Shiel, R.F. Sikora, E.H. Softky, J.B. Spielman, D.B. Snyder, S.L. Snyder, R.W. Tabor, J.M. Thomas, H.M. Van Buren, K. Velasco, S. Waddell, A. Wagini, R.R. Wahl, R. Ward, and C.W. Wilson.

DISCLAIMER

This Compact Disc-Read Only Memory (CD-ROM) publication was prepared by an agency of the United States Government. Neither the United States Government nor the agency thereof nor any of their employees make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.

Although all data and software published on this CD-ROM have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and/or the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data, software, or related materials.

SYSTEM REQUIREMENTS

The data and text on this CD-ROM require either a Macintosh or compatible computer or an IBM or compatible personal computer. The Macintosh should have a 68020 or higher processor (PowerPC recommended), 8 megabytes RAM (16 MB recommended), Apple System Software version 7.0 or later (7.1.2 or later recommended), and a 13-inch color monitor that can display 256 colors. The PC should have a 386 or higher processor (Pentium recommended), Microsoft Windows 3.1 or higher (Windows 95 or Windows NT recommended), 8 megabytes RAM (16 MB recommended), and a VGA color monitor that can display 256 colors.

This CD-ROM was produced in accordance with the ISO 9660 and Macintosh HFS standards. All ASCII and PDF files can be accessed from PC, Macintosh, and Unix platforms, the display software packages provided are designed for use under a PC Windows-based or Macintosh system, as appropriate.

PORTABLE DOCUMENT FORMAT (PDF) FILE

In addition to the ASCII text (1_README.TXT) and data files (in the DATA directory), This disc contains Portable Document Format (PDF) files for viewing and searching documents. The ACROBAT directory contains installers for Adobe Acrobat Reader 3.0 for both Windows (PC directory) and Macintosh (MAC directory, INST_R30 installer). For Windows, a 16- bit version (RS16E30.EXE installer) is provided for Windows 3.1 and a 32-bit version (RS32E30.EXE installer) is provided for Windows NT and Windows 95. The Windows installers are self-extracting archives that open in the directory you specify. Once opened, run the Setup program to proceed. You can use the installers provided on this disc or download the latest version of Adobe Acrobat Reader free via the Internet from the Adobe homepage on the World Wide Web at http://www.adobe.com/ In order to view PDF files you will need a reader that can translate PDF files. This CD-ROM contains a full-text index (INDEX.PDX) that is for use in searching the .PDF files for words or sets of words using the search tool in Acrobat Reader.

Within the DDS_42.PDF file, links (highlighted text) are provided that allow you to jump to another part of document, change views, or display figures. Links to the World Wide Web will access the user's connection to the Internet and browser software if available. The CD-ROM also contains a full-text index (INDEX.PDX and associated subdirectory) that can be used to search for words or phrases using the search tool supplied with Acrobat Reader described above. If your version of Acrobat Reader has a “File” “Preferences” “General...” check box for “Open Cross-Document Links In Same Window,” deselect it; this will keep the main document open when you view another PDF file.

RELATED WORLD WIDE WEB SITES

Western Region Geophysics-http://wrgis.wr.usgs.gov/docs/gump/gump.html
U.S. Geological Survey-http://www.usgs.gov
National Geophysical Data Center-http://www.ngdc.noaa.gov
Nevada Bureau of Mines and Geology-http://www.nbmg.unr.edu
State of Nevada-http://www.state.nv.us

GRAVITY DATA FORMAT AND REDUCTION

Principal facts of gravity data are contained in the DATA directory. The data files are listed in table 1 and are in the ASCII format described in table 2. Accuracy codes, if available, which describe location and observed gravity accuracies, are listed in table 3. Gravity data were reduced using the Geodetic Reference System of 1967 (International Union of Geodesy and Geophysics, 1971) and adjusted to the International Gravity Standardization Net 1971 (IGSN 71) gravity datum (Morelli, 1974). Observed gravity values were ultimately tied to an IGSN 71 network of base stations throughout Nevada described by Jablonski (1974). Gravity data were reduced to complete Bouguer and isostatic anomalies using a reduction density of 2.67 g/cm^3.

Gravity stations were processed by applying standard corrections to the data that include: a field reading to gravity unit conversion, which converts readings in arbitrary units to milligals by using manufacturer's factors and a calibration constant determined by repeated measurements over established calibration loops; an earth-tide correction, which removes the effect of the tidal attraction of the sun and moon; the instrument drift correction, which accounts for nonelastic changes in the instrument's spring and temperature effects; a free-air correction, which accounts for the different elevation of each station; a Bouguer correction, which accounts for the attraction of rock material between the station and sea-level; a latitude correction, which takes into account the variation of the Earth's gravity at sea-level with latitude; the curvature correction, which corrects for the Earth's curvature; a terrain correction, which removes the effect of topography to a radial distance of 167 km; and an isostatic correction, which removes long-wavelength variations in the gravity field and is based on a model of isostatic compensation.

Terrain corrections nearest the station, inner-zone terrain corrections, were calculated using the Hayford-Bowie system (Swick, 1942), the Hammer (1939) system, or by using a digital elevation model and a computer procedure. Terrain corrections farther away from the station, outer- zone terrain corrections, were recomputed for all data using a digital elevation model (fig. 3) and a computer procedure by Godson and Plouff (1988). The extent of the inner-zone terrain correction varies from source to source and, if available, a one-letter code is used to denote its extent (table 1). In general, for USGS data, terrain corrections consist of a three part process: a field terrain correction to a radial distance of 68 or 175 m, a manually estimated inner-zone correction to a radii of 2.29 or 8.95 km, and an outer-zone correction to a radius of 167 km using a computer procedure adapted from Godson and Plouff (1988). A terrain corrected, complete Bouguer gravity map of Nevada is shown in figure 4.

Isostatic corrections were removed from the Bouguer gravity field using a method by Jachens and Roberts (1981). The isostatic model is based on an Airy-Heiskanen model for local isostatic compensation of topographic loads with an assumed sea-level crustal thickness of 25 km, a crustal density of 2.67 g/cm-3, and a density contrast across the base of the crust of 0.4 g/cm-3. A discussion of the isostatic correction and its significance was given by Simpson and others (1986). An isostatic gravity map of the state of Nevada is shown in figure 5.

Table 1. List of gravity data files in the DATA directory

Table 2. Format of gravity data [ft, feet; g/cc, grams/cubic-centimeter; mGal, milligal]

Table 3. Explanation of 4-digit accuracy code [alt, altimetry; blk, black; brn, brown; elev., elevation; NGS, National Geodetic Survey; NMD, National Mapping Division; PG, photogrammetry; USGS, U.S. Geological Survey; VABM, vertical angle bench mark]

SELECTED REFERENCES

Bol, A.J., Snyder, D.B., Healey, D.L., and Saltus, R.W., 1983, Principal facts, accuracies, sources, and base station descriptions for 3672 gravity stations in the Lund and Tonopah 1 X 2 degree quadrangles, Nevada: available from National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22152, PB83-202-671, 86 p.

Bracken, R.E., and Kane, M.F., 1983, Principal facts for gravity stations in the Nevada portion of the Kingman 1 X 2 degree quadrangle: available from National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22152, PB84-103-084.

Chapman. R.H., 1979, Principal facts and accuracies for 857 gravity stations on the Death Valley 1 X 2 degree quadrangle, California and Nevada: California Division of Mines and Geology Open-File Report 77-9, 42 p.

Erwin, J.W., 1982, Principal facts for a set of regional gravity data for the Wells 1 X 2 degree sheet, Nevada: Nevada Bureau of Mines and Geology Open-File Report 82-2.

Erwin, J.W., 1982, Principal facts for a set of regional gravity data for the Millett 1 X 2 degree sheet, Nevada: Nevada Bureau of Mines and Geology Open-File Report 82-3.

Godson, R.H., and Plouff, Donald, 1988, BOUGUER version 1.0, a microcomputer gravity-terrain-correction program: U.S. Geological Survey Open-File Report 88-644-A, Documentation, 22 p.; 88-644-B, Tables, 61 p.; 88-644-C, 5 1/4-inch diskette.

Hammer, Sigmund, 1939, Terrain corrections for gravimeter stations: Geophysics, v. 4, p.184-194.

Harris, R.N., Ponce, D.A., Healey, D.L., and Oliver, H.W., 1989, Principal facts for about 16,000 gravity stations in the Nevada Test Site and vicinity: U.S. Geological Survey Open-File Report 89-682-A, Principal facts documentation, 78 p.; 89-682-B, Gravity data listing on paper, 286 p.; and 89-682-C, Gravity data on diskette, 2 3.5-in diskettes.

Healey, D.L., 1970, Gravity surveys in the California portion of the Kingman quadrangle: U.S. Geological Survey Open-File Report 70-158, 20 p.

Healey, D.L., Wahl, R.R., and Currey, F.E., 1981, Principal facts, accuracies, sources, and base station descriptions for gravity stations in the Nevada part of the Goldfield and Mariposa 1 x 2 degree sheets: U.S. Geological Survey Open-File Report USGS-474-311, 12 p.

Heiskanen, W.A., and Moritz, H., Physical Geodesy: New York, W.H. Freeman, 364 p.

International Association of Geodesy, 1971, Geodetic Reference System 1967: International Association of Geodesy Special Publication no. 3, 116 p.

Jablonski, H. M., 1974, World relative gravity reference network North America, Parts 1 and 2: U.S. Defense Mapping Agency Aerospace Center Reference Publication no. 25, originally published 1970, revised 1974, with supplement of IGSN 71 gravity datum values, 1261 p.

Jachens, R.C., and Roberts, C.W., 1981, Documentation of a FORTRAN program, 'isocomp', for computing isostatic residual gravity: U.S. Geological Open-File Report 81-574, 26 p.

Morelli, Carlo (Ed.), 1974, The International Gravity Standardization Net, 1971: International Association of Geodesy Special Publication no. 4, 194 p.

National Geophysical Data Center, 1988, U.S. Department of Defense gravity files: available from National Geophysical Data Center, National Oceanic and Atmospheric Administration, Mail Code E/Gcx2, 325 Broadway, Boulder, CO 80303.

Plouff, Donald, 1982, Gravity observations in the Walker Lake 1 X 2 degree quadrangle, California-Nevada: U.S. Geological survey Open-File Report 82-405, 105 p.

Plouff, Donald, 1990, Principal facts for gravity data compiled for the Conterminous United States Mineral Appraisal Program, Tonopah 1- by 2- degree quadrangle: U.S. Geological Survey Open-File Report 90-457-A, text, 22 p.; 90-457-B, tables, 61 p.; 90-457-C, 3.5-in diskette.

Plouff, Donald, 1994, Principal facts and field data for gravity data in and adjacent to the Reno 1 X 2 degree quadrangle, Nevada and California: U.S. Geological Survey Open-File Report 94-006-A, text, 16 p.; 94-006-B, 3.5-in diskette.

Plouff, Donald, 1996, Principal facts and field observations for gravity data in and adjacent to the Bureau of Land Management's Winnemucca District and Surprise Resource Area, northwest Nevada and northeast California: U.S. Geological Survey Open-File Report 96-290-A, text, 26 p.; 96-290-B, 3.5-in diskette.

Ponce, D.A., 1992, Principal facts for about 2,800 gravity stations on the Ely 1 x 2 degree quadrangle, Nevada and Utah: U.S. Geological Survey Open-File Report 92-431, 43 p., diskette.

Ponce, D.A., 1996, Bouguer gravity map of Nevada, Elko sheet: Nevada Bureau of Mines and Geology Map 107, scale 1:250,000.

Reidy, D., Kane, M.F., Healey, D.L., Peterson, D.L., and Kaufmann, H.E., 1978, Principal facts for a set regional gravity data for the Las Vegas 10 by 20 sheet, Nevada: U.S. Geological Survey Open-File Report 78-1012, 36 p.

Robbins, S.L., Oliver, H.W., and Huber, D.F., 1975, Principal facts, accuracies, sources, base station descriptions, and plots for 1931 gravity stations on the Mariposa and part of the Goldfield 10 by 20 quadrangles, California and Nevada: available from National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22152, PB-241-469, 79 p.

Saltus, R.W., 1988, Gravity data for the State of Nevada on magnetic tape: U.S. Geological Survey Open-File Report 88-433, 20 p.; 9-track magnetic tape available from User Services Unit, EROS Data Center, Sioux Falls, South Dakota 57198.

Sikora, R.F., 1991, Principal facts for 133 gravity stations, with color maps of Bouguer and isostatic residual gravity anomalies on the Winnemucca 1 X 2 degree quadrangle, Nevada: U.S. Geological Survey Open- File Report 91-256-A, documentation, 40 p., 91-256-B diskette.

Simpson, R.W., Jachens, R.C., and Blakely, R.J., 1986, A new isostatic residual gravity map of the conterminous United States with a discussion on the significance of isostatic residual gravity anomalies: Journal of Geophysical Research, v. 91, no. B8, p. 8,348-8,372.

Snyder, D.B., Tang, R.W., Oliver, H.W., and Morin, R.L., 1982, Principal facts, accuracies, sources, base station descriptions and plots for 2,255 new and revised gravity stations in the western half of the Caliente 1 X 2 degree quadrangle, Nevada and Utah: available from National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22152, PB81-179-780, 101 p.

Swick, C.A., 1942, Pendulum gravity measurements and isostatic reductions: U.S. Coast and Geodetic Survey Special Publication 232, 82 p.

APPENDIX

LIST OF SOURCES FOR DATA FROM THE NATIONAL GEOPHYSICAL DATA CENTER

A list of gravity sources from data obtained from the National Geophysical Data Center for Nevada and adjacent parts of California, Utah, and Arizona is shown below. Their data and source list are available from the National Geophysical Data Center, National Oceanic and Atmospheric Administration, Mail Code E/GCX2, 325 Broadway, Boulder, Colorado 80303, USA. These data are from the Department of Defense- Defense Mapping Agency gravity files and their source codes are contained in the first four digits of the gravity station name (table 2).