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Item Information Circular 14. Index to Geophysical Investigations in Minnesota(Minnesota Geological Survey, 1978) Beltrame, R.J.This report was prepared for the Conference on Geophysics in Minnesota, May 1-2, 1978, at the Radisson Hotel, St. Paul, Minnesota. The purpose of this conference is to discuss the future direction for applied geophysical investigations in the State of Minnesota. This report was prepared as a source of background information on the present status of geophysical studies in the State. A detailed search for information on all aspects of geophysical investigations in Minnesota was undertaken. This report is concerned primarily with geophysical studies involving one or more of the following methods: electrical; electromagnetic; gravity; magnetic; seismic; and radioactive. For the first five topics, an index map and a list of references to areas studied in the state are provided. An index map to Radioactive investigations was not compiled because the numerous small areas of investigations by several investigators make it unfeasible. Also included in this report are selected references to miscellaneous geophysical investigations of a general nature, paleomagnetic studies; and references to studies on the Midcontinent Gravity High of which geophysics has played an important role.Item Information Circular 17. Interpretation of Resistivity Sounding Data: Computer Programs for Solutions to the Forward and Inverse Problems(Minnesota Geological Survey, 1979) Davis, Philip A.Two Fortran computer programs described in this paper offer solutions to the "forward" and "inverse" problems of resistivity sounding. The "forward" problem consists of computing an apparent resistivity curve for some theoretical model. This is accomplished by program RESIST using linear filter theory (Ghosh, 1971a,b). The "inverse" problem consists of finding a theoretical model whose apparent resistivity curve matches a set of field data to reasonable accuracy. Program INVERSE accomplishes this by applying Marquardt's algorithm (Marquardt, 1963) to an initial model, modifying this model iteratively until it produces a match with the field curve. Both programs were written in Minnesota FORTRAN (MNF) for a Control Data Corporation Cyber 74 computer. The basic model used in both programs is an infinite half-space divided into a total of E horizontal layers, each electrically homogeneous and isotropic. The model parameters include the resistivity (R) and the thickness (H) of each layer. The bottom layer is assumed infinite in extent, so there are a total of 2E-1 parameters. Real field situations will not normally match these ideal conditions. Deviations from the model will produce errors in the field data, although if these errors are relatively small, a layered model interpretation is still possible. This paper does not address interpretation problems such as equivalence or suppression. For a discussion of these, see Davis (1979) or Mooney (1979) and references therein.Item Information Circular 35. Geophysical Solutions to Geologic Problems of Continental Interiors: A Minnesota Workshop(Minnesota Geological Survey, 1991) Chandler, V.W.Geophysics has long been a companion to geologic studies in Minnesota, where most of the bedrock lies beneath a thick cover of glacial drift. In 1979 the Minnesota Geological Survey (MGS), through funding by the Legislative Commission on Minnesota Resources (LCMR), began an ambitious geophysical project-a state-wide program of high-resolution aeromagnetic surveying. On the occasion of the completion of this highly successful program, the MGS through LCMR support hosted an international geophysics workshop during March 3-6,1991. The main objective of the workshop was to determine how the LCMR data and other geophysical information can most effectively be used, and what sorts of new geophysical investigations are desirable for Minnesota. Such an assessment must address private, academic, and governmental needs and must consider a diversity of topics, including mineral exploration, environmental and ground-water studies, geologic mapping, and crustal studies. The recommended tasks must also be consistent with the MGS mission of geologic mapping and framework studies. Sessions were centered on near-surface studies, geologic mapping, mineral exploration, and crustal studies. Speakers were selected from diverse perspectives and included individuals from the United States, Canada, Australia, and Finland. Posters included presentations by some of the speakers, as well as other geophysicists working in the region. The workshop attracted over 100 earth scientists, representing 10 states and 4 countries, and the sessions stimulated many useful discussions and ideas. This report summarizes the workshop, and discusses some of its most important recommendations. These recommendations will help set the course for Minnesota geophysics into the 21st century.Item OFR07-06, Upgrade of Aeromagnetic Databases and Processing Systems at the Minnesota Geological Survey(Minnesota Geological Survey, 2007) Chandler, Val WDuring 2005-2007 a program to upgrade the aeromagnetic database for Minnesota was conducted by the Minnesota Geological Survey (MGS). Most of the Minnesota aeromagnetic data were acquired during a 1979-1991 state-wide survey program, and compilation and processing were limited to the computer capabilities of the time. Since that time significant improvements have been made in the development of computers and software that can efficiently handle massive database operations, such as line leveling and gridding. This project was consequently initiated to upgrade the MGS database using up-to-date software and hardware. Access to the data was also to be improved by making all upgraded data available via the web.Item OFR11-03, Compilation of Minnesota and Western Wisconsin Geoscience for the USGS National Geologic Carbon Dioxide Sequestration Assessment: Enhanced Geophysical Model for Extent and Thickness of Deep Sedimentary Rocks(Minnesota Geological Survey, 2011) Chandler, V.W.; Lively, R.S.In 2010, the Minnesota Geological Survey (MGS) was commissioned by the U.S. Geological Survey (USGS) to clarify available knowledge on the rocks that are most prospective for subsurface carbon dioxide sequestration in Minnesota and western Wisconsin. Although the prospective rocks, late Precambrian sedimentary basins of the Midcontinent Rift system (MRS), are at depths greater than the 1 km depth required for efficient carbon dioxide storage, and there is some potential for adequate porosity, permeability, and seals, the overall prospects for reservoir suitability are not promising from several perspectives. Nevertheless, the current USGS National Geologic Carbon Dioxide Sequestration Assessment project is presently seeking to clarify potential sequestration sites across the US. In response to a request from the USGS under this program, therefore, a summary of knowledge was assembled and enhanced, to provide the best readily available information on inferred geological tops, cross-sections, maps, geological history, and likely composition of the potential reservoirs and seals.