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Principal Facts of Gravity Stations Used for Complete A cooperative project of the Utah Geological and Mineral Survey, the United States Geological Survey, and the Department of Geology and Geophysics, University of Utah.
OUTLINE Abstract
APPENDICES Appendix A -- Key to designations of gravity stations used for the gravity map of Utah. FIGURES Figure 1 -- Columns and rows of USGS grids. Return to the Top of this Document ABSTRACT This report describes (1) the principal facts (observed gravity, elevation, latitude, longitude, terrain corrections, complete Bouguer anomaly, and free-air anomaly) of approximately 42,000 gravity stations and (2) these data interpolated to a 2.5-km square grid that were used to compile the complete Bouguer gravity anomaly map of the state of Utah (Cook and others, 1989). The project was a cooperative effort of (1) the Utah Geological and Mineral Survey (UGMS), (2) the United States Geological Survey (USGS), and (3) the Department of Geology and Geophysics, University of Utah. The gravity data were established by many individuals and organizations over a 30-year period. The 42,000 gravity stations comprise about 33,500 stations that were supplied by K.L. Cook from files of the University of Utah, and about 8,500 stations that were added by Viki Bankey from the files of the National Geophysical Data Center (of the National Oceanographic and Atmospheric Administration) and the USGS. The merging and processing of the data were done by Viki Bankey in the USGS Denver office. This report also describes in some detail the methods of compiling, processing, and reduction of the gravity data and also the editing of the preliminary worksheet copies of the gravity contour maps. These editing efforts were especially effective in eliminating as many “bad stations” as possible in the various data sets and thus providing a more accurate final set of data. Much of the gravity data is from the University of Utah files, and the sources of these data, especially from former students at the University and various petroleum companies, are acknowledged specifically herein. Also many different sources of financial support for the gravity research effort under the supervision of K.L. Cook at the University of Utah over a 30-year period are acknowledged specifically. The final data set was produced by Viki Bankey in the USGS Denver office. One file contains the principal facts of the gravity stations. A second file contains these data interpolated to a 2.5-km square grid. The 9-track magnetic tape containing the data was written at a density of 1600 bits per inch in ASCII format with a blocksize of 4000 bytes and a logical record size of 80 bytes. Return to the Top of this Document BACKGROUND INFORMATION The first published gravity map of Utah was prepared by K.L. Cook, J.R. Montgomery, J.T. Smith, and E.F. Gray and published by the Utah Geological and Mineral Survey (UGMS) in 1975 (Cook and others, 1975). This is a simple Bouguer gravity anomaly map at a scale of 1:1,000,000 based on approximately 27,000 gravity stations. In several areas of the state the data used to prepare this map were too sparse to adequately define the regional gravity anomalies, and the lack of terrain corrections limited the usefulness of the map in areas of high topographic relief. By 1981 digital terrain data that could be used to compute the terrain corrections necessary to prepare a complete Bouguer gravity anomaly map of Utah were available, and a geologic map of the state had been published at a 1:500,000 scale (Hintze, 1980). To produce a complete Bouguer gravity anomaly map of Utah at the scale of the geologic map a cooperative program between the University of Utah, the Utah Geological and Mineral Survey (UGMS), and the U.S. Geological Survey (USGS) was developed. K.L. Cook and D.R. Mabey, who was then with the USGS, developed preliminary plans for the map, and Donald T. McMillan, then Director of the UGMS, agreed that the UGMS would publish the map. General plans for the cooperative effort were agreed to in 1984 by Cook, Mabey, now representing the UGMS, and John DeNoyer and M. Dean Kleinkopf (USGS), and a cooperative agreement was signed in 1985 making the effort part of the Federal-State Cooperative Geologic Mapping (COGEOMAP) program. In addition, a memorandum of understanding between Cook and the UGMS was signed defining the responsibilities of K.L. Cook and the UGMS in compiling and publishing the gravity map. The objectives of the cooperative project were to compile and publish a complete Bouguer gravity anomaly map of Utah at a scale of 1:500,000 and make available to the public a digital data set of the principal facts of the gravity stations used to compile the map. This data set is to include the data from the University of Utah files that were not readily available to the public. The major responsibilities were: 1. Cook to provide gravity data from the University of Utah files in digital form.Viki Bankey became responsible for the USGS effort, and Michael DePangher assisted Cook in his effort. At the start of the compilation effort, the gravity data for Utah consisted of data from numerous surveys and compilations. These surveys and compilations involved a variety of data reduction and data storage procedures and often overlapped so that data from one station was duplicated in two or more compilations. Editing and merging the data was a complicated task. Return to the Top of this Document COMPILATION OF UNIVERSITY OF UTAH DATA Compilation work on the University of Utah gravity data was begun by Cook and students working under his supervision. Financial support for this work at the University of Utah was provided by grants-in-aid to the University of Utah from the organizations and individuals listed in the Acknowledgments. Also at this time Cook obtained written permission from the officials of various petroleum companies (also listed in the Acknowledgments) that had previously donated to him and/or the University of Utah gravity data in Utah (1) to use these data for the new gravity map of Utah and (2) to include the list of principal facts of these gravity stations with all the other stations used in making the gravity map, and to publish the list of principal facts of all of these stations after final publication of the map. A magnetic tape containing the principal facts of about 37,000 gravity stations in Utah compiled by K.L. Cook and John C. Groenewold was forwarded to the U.S. Geological Survey on September 24, 1985, for processing by the USGS. This list of stations comprised: 1) About 27,000 stations that were included on the simple Bouguer gravity anomaly map of the state of Utah (Cook and others, 1975).The 37,000 stations submitted to the USGS for processing had been assembled at the University of Utah over a 30-year period from many different separate data sets of gravity stations that had been established by many individuals and organizations. It was desirable to preserve, insofar as possible, the identity of each separate data set; and this was generally done by keeping the original station designations in the list of principal facts of the stations. It should be emphasized that each of the various data sets had been adjusted to the gravity base station network in Utah established in 1967 by the U. S. Army Map Service in a cooperative project with the Department of Geophysics, University of Utah (Cook and others, 1971). Before submitting the 37,000 stations to the USGS, and intermittently thereafter, the entire University of Utah data sets were carefully edited by K.L. Cook, Michael DePangher, and John C. Groenewold using the digital computer to compare the observed gravity values of the approximately 3,000 repeat stations within the University data sets. This study included (1) repeat stations within the same data sets for individual gravity surveys and (2) duplicate stations at the same location in different data sets for separate gravity surveys made at different times over a 30-year period. Using the digital computer, the principal facts of the gravity data for these repeat and duplicate stations were grouped together conveniently on computer printout listings for rapid comparison and analysis to detect errors and discrepancies between the various gravity surveys. Also, this information provided a measure of the accuracy of the gravity data for individual surveys and facilitated in making any necessary adjustments of the gravity data between different surveys. After adjustments of the gravity data between different surveys, a comparison of the observed gravity values of the repeat and duplicate stations showed that generally there was excellent consistency -- within 0.3 milliGal (i.e., within maximum tidal effect) --, which was gratifying. If the comparison showed a difference that exceeded 0.5 mGal, the bad station was generally discarded. However, in mountainous areas with difficulty of access and often poorer elevation control, stations with possible errors exceeding 0.5 mGal, and rarely exceeding 1.0 mGal, were retained. Accordingly, most of the stations are believed to be correct within 0.5 mGal in the valley areas and within 1.0 mGal in the mountainous areas. Return to the Top of this Document MERGING AND PROCESSING OF DATA The merging and processing of the gravity data were done by Viki Bankey in the USGS Denver Office. The 37,000 stations -- including the 3,000 repeat and duplicate stations -- provided by Cook were used as the basic data set and were supplemented by about 9,000 stations taken by Bankey from the files of the National Geophysical Data Center (of the National Oceanographic and Atmospheric Administration) and the USGS, collectively designated herein as “NOAA data”. Thus, a total of about 46,000 stations (including repeat and duplicate stations) were used for the preliminary compilation for the entire state of Utah, for which the gravity data extended a distance of about 15 minutes of arc (approximately 25 km (15 miles)) beyond the Utah state border in all directions in order to reduce “edge effect” in the computer contouring. In merging the Cook and NOAA data sets, the Cook data set was given priority in the following manner: (1) To facilitate the gridding program (to be used later), only one gravity value was accepted by the computer for each station location, which was defined as lying within 0.15 minute of arc (about 250m (750 ft)) of the latitude and longitude of a given station. The observed gravity values for the 42,000 stations used to compile the map were first adjusted to conform to the International Gravity Standardization Net of 1971 (International Association of Geodesy, 1974) as follows: (1) By first accepting the observed gravity values of all 37,000 Cook stations (plus 9,000 NOAA stations), which had gravity data sets that were already adjusted to the gravity base station network in Utah established in 1967 (Cook and others, 1971).The adjusted observed gravity values were then reduced to the simple Bouguer gravity anomaly values using the 1967 gravity formula (International Association of Geodesy, 1971) at a reduction density of 2.67 g/cm3. Standard USGS reduction equations and related expansions are explained in Cordell and others (1982). Computer-calculated terrain corrections, assuming a rock density of 2.67 g/cm3, were made radially from each station to a distance of 167 km (100 miles) using the method of Plouff (1977). The two separate terrain-correction values--one for the inner zones and one for the outer zones--were added to give the total terrain-correction value for each station. The total terrain-correction value was then added algebraically to the simple Bouguer gravity anomaly value to give the complete Bouguer gravity anomaly value for each station. Return to the Top of this Document PREPARATION OF MAP The map was prepared on a Lambert Conformal Conic projection based on standard parallels 33 degrees and 45 degrees and with a central meridian longitude of 111.2500 degrees W and a base latitude of 36.7500 degrees N. The irregularly spaced complete Bouguer gravity anomaly values were gridded at a 2.5-km spacing using a computer program by Webring (1981) based on minimum curvature (Briggs, 1974). The gridded data were contoured at a 5-milliGal interval using a program by Godson and Webring (1982), with contour smoothing using splines under tension. Minor corrections to the computer contouring were made by hand. The contour map originally extended beyond the state boundary about 15 minutes of arc (about 25 km (15 miles)) in all directions to reduce “edge effect” in the computer contouring, and was trimmed by hand to ensure accuracy at the map edges. The inferred dashed contours (drawn by hand) in the two following areas are to be considered approximate only because the contours were taken (and adjusted) from former gravity maps of known high quality for which the principal facts of the gravity stations are no longer available: 1. Ogden Valley area -- contours were taken (and adjusted) largely from Stewart (1970). No principal facts were available. Return to the Top of this Document EDITING OF MAP The map was edited by K.L. Cook and D.R. Mabey with the assistance of M. DePangher. To facilitate editing of the map, preliminary worksheet copies of the machine-contoured gravity maps -- in the form of 1 degree x 2 degree quadrangle maps at a scale of 1:250,000 (and contour interval of 2 mGal and a grid-interval of 1.5 km) of the entire state of Utah -- were prepared by Viki Bankey. A total of 14 different quadrangle maps for Utah were thus prepared. The process of recognizing and eliminating the “bad stations” was accomplished by recognizing large, erroneous, “bulls-eye” one-station anomalies on the preliminary machine-contoured worksheet gravity maps and omitting them from the data sets. Also, in many areas, by consulting geologic and/or topographic maps, many bad stations were eliminated so that the gravity contours would conform better with the known geologic and/or topographic features -- as, for example, Basin and Range faults. Many of the eliminated stations were at unreasonable locations indicating errors in either the latitude or longitude. Note: The total number of bad stations rejected in the editing process were too few to alter materially the above-discussed statistics of the stations rejected because they were repeat or duplicate stations. Later, a second set of preliminary worksheet copies of similar maps at a scale of 1:250,000 and contour interval of 2 mGal and grid interval of 2.0 km were prepared and edited to detect and eliminate bad stations not previously recognized.Next, various versions of the complete Bouguer gravity anomaly map of the entire state at a scale of 1:500,000 and 5-mGal contour interval were prepared. The map with a 2.5-km grid interval is preferred, and was used as a worksheet map for editing the “final model copy”. Finally, a camera-ready copy was prepared on scribecoat, under the supervision of Bankey, by the National Mapping Division of the USGS in Denver; and this copy was transmitted to the UGMS office in Salt Lake City for final preparation for publication (Cook and others, 1989). 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COMPARISON OF NEW MAP AND For those people and organizations using the new gravity map and data, and especially those who may wish to merge their own gravity data in Utah with the data included in the principal facts of gravity data listed on the new magnetic tape (see below), it will be helpful to discuss here a comparison between the new gravity map and data with the old gravity maps and data. To compare the new gravity map and data with old gravity maps and data, some of the basic principles of the reduction of gravity data need to be considered. In this discussion, “old gravity maps and data” will refer especially to the former maps of parts of Utah compiled by Cook and students and gravity data used for these former maps. For the old gravity maps and data, the reduction of the gravity data used (1) the theoretical gravity at mean sea level based on the 1930 International gravity formula and (2) a combined total elevation correction factor taken as +0.06 mGal/ft (which is the “rounded” value (from 0.05999 mGal/ft (0.19683 mGal/m)) that includes a free-air correction of 0.09406 mGal/ft (0.30861 mGal/m) and a Bouguer correction of -0.03407 mGal/ft (0.11178 mGal/m) for an assumed rock density of 2.67 g/cm3 and a universal constant of gravitation value of 0.6667 x 10-07 cgs units. For the new gravity map and data, the present USGS method of reduction of the gravity data, as explained in detail by Cordell and others (1982), uses: (1) the theoretical gravity at mean sea level based on the new 1967 gravity formula (as discussed earlier); (2) a separate computation for the free-air correction, which varies with latitude; (3) a separate computation for the Bouguer correction (-0.1119 mGal/m); and (4) in addition, a “Earth's curvature correction” term, which is a modification of the Bouguer slab approximation. The “datum correction” used by Bankey is -13.74 mGal. It should be noted that -- as pointed out by Woollard (1979, p. 1364-1365) -- the datum correction is the same sign as the difference in theoretical sea level gravity used in the old (1930) International gravity formula and the new (1967) gravity formula (used for the new gravity map), which varies from - 17.15 mGal at the equator to -3.58 mGal at the poles. However, in the conversion of Bouguer anomalies from the old to the new system, the datum correction is applied with regard to sign as a negative quantity and the latitude correction with sign reversed as a positive quantity. Accordingly it can be reasoned, by using Table 1 of Woollard (1979, p.1353), that for a gravity station at latitude 38 degrees (for example) and at sea level (where the free-air, Bouguer, and Earth's curvature corrections may be assumed zero), the Bouguer gravity anomaly value, using the new (1967) system and the datum correction of -13.74 mGal used by the USGS, is 1.74 mGal less algebraically than the corresponding Bouguer gravity anomaly value obtained in the old (1930) system. (This value is obtained by algebraically adding the value of -13.74 mGal (datum correction used by Bankey) and +12.00 mGal (taken from the “difference” column, for latitude 38 degrees, in Woollard's above-mentioned Table 1). Obviously, this value changes slightly with latitude (about 0.23 mGal per degree of latitude at 38 degrees latitude; see Table 1 of Woollard). By making an actual comparison between the complete Bouguer gravity anomaly values obtained from the new (1967) and old (1930) systems, one can demonstrate that the above analysis is correct for both the new gravity map of Utah and the new principal facts of gravity stations as contained in the listing on the magnetic tape. In particular, a comparison was made in selected areas and for selected stations in the region between latitude 38 degrees and 39 degrees on the complete Bouguer gravity anomaly map of the Richfield 1-degree x 2-degree quadrangle (Cook and others, 1981), and compared with the corresponding areas and stations on the new gravity map of Utah. The comparison shows that, at these latitudes, the complete Bouguer gravity anomaly values obtained from the new (1967) system are about 4 mGal less algebraically than the corresponding complete Bouguer gravity anomaly values obtained from the old (1930) system. The apparent discrepancy between (1) the approximately 4-mGal difference for actual stations in the Richfield quadrangle at latitudes of about 38 degrees and at elevations of 5,000 feet to 9,500 feet and (2) the 1.74-mGal difference for a station at sea level at latitude 38 degrees can be explained by the differences in the method of data reduction between the old (1930) system used by Cook and students and the new (1967) system used by the USGS. In particular, different formulas were used in the two systems for (1) free-air corrections and (2) Bouguer corrections; and the Earth's curvature correction term was used in the new (1967) system only. To summarize, it should be emphasized that the complete Bouguer gravity anomaly values on the new gravity map of Utah and listed in the principal facts of gravity stations in the magnetic tape (see below) -- which were obtained using the present USGS method of data reduction with the new (1967) system -- are algebraically less by several milliGals (the exact value depending on latitude and station elevation) than the complete Bouguer gravity anomaly values given for the corresponding stations on gravity maps and gravity data published and/or open filed by Cook and students using their above-discussed method of data reduction with the old (1930) system. Note: In making a comparison of maps, it should be noted that the new gravity map of Utah was computer-contoured using the gravity data interpolated to a 2.5-km square grid. Therefore the location of contour lines on this map may be slightly shifted from the more exact location of the corresponding contour lines on a map that had instead been contoured by hand using the exact complete Bouguer gravity anomaly values at the irregularly spaced stations. However, the difference between (1) the computer-generated contours and (2) contours that might otherwise be derived by hand-contouring the complete Bouguer gravity anomaly values of irregularly spaced stations is too small to change the above conclusion: namely, that the contoured Bouguer gravity anomaly values on the new map are algebraically less by several milliGals than the corresponding contoured-by-hand or computer- contoured Bouguer gravity anomaly values at the same station using the old (1930) system, as discussed above.Finally, in making a comparison of old and new gravity data and maps, the accuracy of the terrain corrections is very important. It should be emphasized that the terrain data and terrain-correction program used by the USGS in computing the complete Bouguer anomaly values for the new map differ from those used to prepare gravity maps in Utah before 1989. In areas of high local topographic relief the difference in terrain corrections and the complete Bouguer gravity anomaly values based on different sets of terrain data and different computation methods may be several milliGals. Terrain corrections computed for the new map are more accurate than those computed for most earlier maps. The new terrain corrections may be either larger or smaller but because they are likely to be more complete they will most commonly be larger than the earlier values. Increasing the terrain correction algebraically increases the complete Bouguer gravity anomaly value. Therefore, because this effect manifests itself in an opposite sense algebraically from that discussed above, comparisons of new and old gravity data in areas of very high local topographic relief should be made with caution. Return to the Top of this Document ACKNOWLEDGMENTS The following petroleum companies donated gravity data to K.L. Cook and/or the University of Utah and have given written permission (1) to use these data for the new gravity map of Utah and (2) to include the list of principal facts of these gravity stations with all the other stations used in making this map, and to eventually publish the list of principal facts of all these stations after final publication of the map: Amoco Production Company *Since June 1984, the following organizations and individuals have provided one or more grants-in-aid to the University of Utah to support gravity research under the supervision of K.L. Cook that included the compilation, reduction, and editing of gravity data used for this map: Amoco Production Company *During the 30-year period prior to June 1984, financial support for the original measurements and compilations of the gravity data by the University of Utah was giving by many of the organizations and individuals previously listed (and indicated with an asterisk) and, in addition, the following: National Science Foundation; U.S. Geological Survey; Department of Energy (Division of Geothermal Energy); Utah Geological and Mineral Survey; American Smelting and Refining Company; Bear Creek Mining Company; Continental Oil Company; H.V.W. Donohoo; Kennecott Copper Corporation; Marathon Oil Company; Phelps Dodge Corporation; Shell Oil Corporation; Texaco Inc.; The Anaconda Company; and various entities of the University of Utah, namely the Computer Center, the Department of Geology and Geophysics, the Engineering Experiment Station, the Uniform School Fund, and the University Research Fund. The support was largely in the form of fellowships or grants-in-aid to students and/or faculty of the University of Utah. Beginning October 1, 1985, additional support for the UGMS and USGS was provided by including the compilation and publication of the new gravity map of Utah as one of the facets of the new Federal-State Cooperative Geologic Mapping (COGEOMAP) program between the state of Utah and the federal government (Oviatt and Davis, 1987; Mabey, 1987; Reinhardt and Miller, 1987). A listing of principal students involved in the gravity surveys, too numerous to acknowledge individually on the published map, is included on the magnetic tape of the principal facts of the gravity data (see Appendix A below). John C. Groenewold (during 1984-1985), former graduate student at the University of Utah, ably assisted K.L. Cook in the preliminary compilation, reduction, and editing of the University of Utah gravity data used for this gravity map. Encouragement for this project has been given especially by Donald T. McMillan and Genevieve Atwood, Directors of the UGMS; John Denoyer and M. Dean Kleinkopf, USGS; William P. Nash, Robert B. Smith, and Frank H. Brown, University of Utah. Return to the Top of this Document REFERENCES Bankey, Viki, 1985, Description of magnetic tape containing Idaho state gravity anomaly data: U.S. Geological Survey unpublished report; U.S. Dept. of Interior, EROS Data Center, 5p. Bankey, Viki, Webring, Michael, Mabey, D.R., Kleinkopf, M.D., and Bennett, Earl, 1985, A Bouguer gravity map of Idaho: U.S. Geological Survey MF- 1773, scale 1:500,00. Briggs, I. C., 1974, Machine contouring using minimum curvature: Geophysics, v. 39, no. 1, p. 39-48. Cook, K.L., Adhidjaja, J.I., and Gabbert, S.C., 1981, Complete Bouguer gravity anomaly and generalized geology map of Richfield 1-degree x 2- degree quadrangle, Utah: Utah Geological and Mineral Survey Map 59; scale 1:250,000; contour interval 2 mGal. Cook, K.L., Bankey, Viki, Mabey, D.R., and DePangher, Michael, 1989, Complete Bouguer gravity anomaly map of Utah: Utah Geological and Mineral Survey Map No. 122, scale 1:500,000, contour interval 5 milliGals. Cook, K. L., Berg, J. W., Jr., Johnson, W. W., and Novotny, R. T., 1966, Some Cenozoic structural basins in the Great Salt Lake area, Utah, indicated by regional gravity data: in Guidebook to the Geology of Utah, No. 20, Wm. Lee Stokes, Editor, Utah Geological Society, Salt Lake City, 1966, p. 57-75. Cook, K. L., Montgomery, J. R., Smith, J. T., and Gray, E. F., 1975, Simple Bouguer gravity anomaly map of Utah: Utah Geological and Mineral Survey Map 37, scale 1:1,000,000, contour interval 5 milliGals. Cook, K. L., Nilsen, T. H., and Lambert, J. F., 1971, Gravity base station network in Utah--1967: Utah Geological and Mineralogical Survey Bulletin 92, 57 p. Cordell, Lindrith, Keller, G. R., and Hildenbrand, T. G., 1982, Bouguer gravity map of the Rio Grande Rift, Colorado, New Mexico, and Texas: U. S. Geological Survey Geophysical Investigations Series, Map GP-949, scale 1:1,000,000. Defense Mapping Agency, 1974, World Relative Gravity Reference Network, North America, Part 2: St. Louis, Missouri, Aerospace Center, DMAAC Reference Publication 25, with supplement updating gravity values to the International Gravity Standardization Net 1971, 1635 p. Godson, R. H., and Webring, M. W., 1982, CONTOUR: A modification of G. I. Evendon's general purpose contouring program: U. S. Geological Survey Open-File Report 82-797, 73 p. Hintze, L.F., 1980, Geologic Map of Utah: Utah Geological and Mineral Survey; scale 1:500,000. International Association of Geodesy, 1971, Geodetic Reference System, 1967: International Association of Geodesy Special Publication No. 3, 116 p. International Association of Geodesy, 1974, The international Gravity Standardization Net 1971: International Association of Geodesy Special Publication No. 4, 194 p. Mabey, D. R., 1987, COGEOMAP--Update on geophysical maps: Utah Geological and Mineral Survey, Survey Notes, Summer/Fall 1987, p. 7. Oviatt, C. G., and Davis, F. D., 1987, COGEOMAP: Utah Geological and Mineral Survey, Survey Notes, Summer/Fall 1987, p. 2-7. Plouff, Donald, 1977, Preliminary documentation for a FORTRAN program to compute gravity terrain corrections based on topography digitized on a geographic grid: U. S. Geological Survey Open-File Report 77-535, 43 p. Reinhardt, Juergen, and Miller, D. M., 1987, COGEOMAP: A new era in cooperative geologic mapping: U. S. Geological Survey Circular 1003, 12 p. Stewart, S. W., 1958, Gravity survey of Ogden Valley in the Wasatch Mountains, north-central Utah: American Geophysical Union Transactions, v. 39, p. 1151-1157. Webring, M. W., 1981, MINC: A gridding program based on minimum curvature: U. S. Geological Survey Open-File Report 81-1224, 41 p. Woollard, G. P., 1979, The new gravity system--changes in international gravity base values and anomaly values: Geophysics, v. 44, no. 8, p. 1352-1366. Return to the Top of this Document DESCRIPTION OF MAGNETIC TAPE A magnetic tape containing the principal facts (observed gravity, elevation, latitude, longitude, terrain corrections, complete Bouguer anomaly, and free air anomaly) of the finally accepted 41,960 gravity stations, as well as the 2.5-km gridded data, used in making the gravity map of Utah was prepared by Viki Bankey. The number of gravity stations listed on this tape differs from the total number of gravity stations (approximately 46,000) stated in the “Discussion” on the published gravity map of Utah (Cook and others, 1989) because the latter figure included repeat and duplicate stations. The tape is available from EROS Data Center, Data Services Officer, Sioux Falls, South Dakota 57198. The listing of the principal facts of the gravity stations includes the sources of the original data which have been arranged to preserve, insofar as possible, the groupings of the individual gravity data sets of the various individuals and organizations that have made the field measurements. In particular, the various individuals and organizations may be identified by the letter or number designations of the individual gravity stations (see Appendix A), for which the original coding has been preserved when practical. It should be noted specifically that the principal students involved in the University of Utah gravity surveys, who were too numerous to acknowledge individually on the published map, are identified in the listing in Appendix A. The two following sections, which give the detailed descriptions of (1) the tape format and (2) the tape file header, are taken from an unpublished USGS report by Bankey (1985), which she prepared to describe the magnetic tape containing the gravity anomaly data used for the gravity map of Idaho (Bankey and others, 1985). Tape Format The 9-track magnetic tape was written at a density of 1600 BPI and contains files of data records in an unlabelled ASCII format. Block size is 4000 bytes and logical record size is 80 bytes. The first 10 lines of each file contains descriptive information about the files. Data records begin on line 11. Tape file header and data description The FORTRAN format identifier describing each record is given in brackets following the entry description. Line 1: type of file stored on tape (1=grid, 2-6=binary,
7-8=ASCII) [a9,i5] creation date [a66]
FILETYPE= 2 CREATION DATE: 12-FEB-1990 10:38:54.47 UTAH88FIN.POS
Following is a description and FORTRAN format of each record for each of the 41,960 gravity stations of file 1:
Following is the header record and first 5 data lines of file 2: FILETYPE= 1 CREATION DATE: 12-FEB-1990 10:29:32.59 UTAH88FIN.GRD
Following is a description and FORTRAN format of the data contained in the second file on the tape containing the gridded data. A row is defined as a series of data positions that extend from west to east along a common north coordinate. The first value in each row contains a “0”, which indicates an evenly spaced grid. The first row is the southernmost (see fig. 1). Dvals (dummy values) are used to indicate areas of no data and have a value of 0.1000E+31. Line 1-10: Header record
where line 11 contains the first 5 elements of row 1; line 12 contains the second 5 elements of row 1, and so on, until all elements in the grid are exhausted.
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APPENDIX A
The original designations of the gravity stations used for the gravity map of Utah have been preserved in so far as possible, in order that the original sets of gravity data can be identified if desired. Generally each of the different gravity surveys has been coded by either (1) a letter designation or (2) a code-number designation. In the following lists, the letter or code-number designation is given, together with other pertinent information, when available, such as party chief or investigators, source of gravity data, date of survey, and area of survey. Letter Designations
Return to the Top of this Document Code-Number Designations
4-digit designations for NOAA data (assigned by Defense Mapping Agency). This list includes references if 15 or more stations from the original data set is included in the data for the state of Utah and vicinity. The Utah data set of 41,960 stations has preserved the original 15-minute boundary and so includes data from adjoining states. NOTE: some of the data sets below do not have unique identifiers for each gravity station: for example, all of the data from set 6203 are labelled “6203 1”. References below have been furnished by the Defense Mapping Agency, and are in chronological order.
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