The Decade of North American Geology - Digital Data |
|
The Decade of North American Geology (DNAG) Project is the centerpiece publication project for the Geological Society of America's Centennial. This massive effort involved participants from over 100 universities, 20 provincial and state geological surveys, 23 oil or mining companies or consulting firms, 18 countries, and 23 agencies in the United States, Canada, Mexico, Central and South America, Greenland, and Israel.
Dr. A.R. Palmer The DNAG Project of the 1980's resulted in published synthesis volumes and wall maps summarizing the geology, tectonics, magnetic and gravity anomaly patterns, regional stress fields, thermal aspects, seismicity, and neotectonics of North America and surrounding ocean areas. Together, the synthesis volumes and maps represent the first coordinated effort to integrate all available knowledge about the geology and geophysics of a crustal plate on a regional scale. The National Geophysical Data Center (NGDC) made several contributions to the DNAG Project including map production, authorship, and editorial review. In addition, NGDC serves as distribution center for much of the digital data resulting from the Project. NGDC is no longer distributing the DNAG CD-ROM product. We regret we cannot support the aged access software. The data contained on the CD-ROM are now available in various formats on-line. Magnetics Data The magnetic data were developed in order to produce the Magnetic Anomaly Map of North America (1987; scale 1:5,000,000; William J. Hinze and Peter J. Hood, co-chairmen of map committee). The final version of the data was compiled by the Geological Survey of Canada (Ottawa) from original ship-track, flight-line, and gridded data, as well as compiled regional maps. The data were then uniformly gridded at a 2-kilometer spacing based on a spherical North American Transverse Mercator projection. The entire data set contains over 2 million grid values, covering an area from 80-degrees North to northern South America. Large amounts of marine magnetic data are also included.
Data are provided in ascii_xyz files (containing latitude, longitude, and aeromagnetic anomaly value), binary raster grid data and associated headers for the Idrisi32 GIS, shape file and associated files of contoured aeromagnetic data (format developed by ESRI), and in the original binary grids. Gravity Data The gravity anomaly data, based on the same projection above, were gridded at 6 kilometers and contain over 5 million grid values. These were used to produce the DNAG Gravity Anomaly Map of North America (1987; scale 1:5,000,000; James G. Tanner, chairman of map committee). The data represent Bouguer gravity anomalies on land and free-air anomalies over the oceans. Technical aspects of data compilation, editing, and gridding were provided by the U.S. Geological Survey.
Data are provided in ascii_xyz files (containing latitude, longitude, and aeromagnetic anomaly value), binary raster grid data and associated headers for the Idrisi32 GIS, shape file and associated files of contoured aeromagnetic data (format developed by ESRI), and in the original binary grids. NOTE: Not all of the data shown on the maps are included in the gridded digital data sets. Gridded digital magnetic data are not available for Greenland, Mexico, and Central America. Gridded digital gravity data are not available for Mexico. Seismicity Data Construction of the DNAG seismicity data base required the analysis of more than one-half million earthquake epicenters from global, national, regional, and local catalogs, and other source materials. Duplicate entries were removed regionally--based on a comparison of reported origin times, epicentral locations, and magnitudes. The edited data base spans an interval from 1534 to 1985. These data were depicted on the Seismicity Map of North America (1988; scale 1:5,000,000; E.R. Engdahl, USGS, chairman of working group and compiler, and W.A. Rinehart, NGDC, preparer). Crustal Stress Data Four main types of tectonic stress indicators are included in the crustal stress data base: earthquake focal mechanisms, wellbore elongations, in situ stress measurements, and young geologic data including volcanic alignments and fault slip analyses. The data were provided by Mary Lou Zoback of the U.S. Geological Survey. They were compiled as part of theWorld Stress Map project of the International Lithosphere Program.
Thermal Aspects Data A comprehensive data base of heat flow and ancillary measurements for North America was compiled as a basis for the DNAGThermal Aspects Map of North America. Information about each site includes hole location and date of temperature measurement, range of values, gradient and heat flow results per depth interval, lithologic information, and comments. Data were compiled by David D. Blackwell, John L. Steele, and Larry S. Carter, Southern Methodist University. Ordering Information DNAG maps and publications may be ordered from the Geological Society of America, Publication Sales, P.O. Box 9140, Boulder, CO, 80301. Please direct telephone inquiries to 1-800-GSA-1988 (or 303-447-2020). |