A Seismic Reflection Survey of the Surface of the Basement Complex in Indiana

Indiana Geological Survey Report of Progress 18The surface of the basement complex that underlies five counties in southwestern Indiana has been mapped by the reflection seismograph method. Seismic shot points were spaced 1 to 3 miles apart along six traverses in Gibson, Pike, Posey, Vanderburgh, and Warrick Counties. A structure map on the surface of the basement complex shows an elongate northwestward-trending depression that is as much as 22 miles in width and that has a maximum depth of 3,500 feet below the regional slope of the basement surface. Structure maps drawn on the surface of Devonian limestone, the Trenton Limestone, and the St. Peter Sandstone show a monocline over the northeast flank of this basement depression. The depression in the surface of the basement complex and the monocline shown on Paleozoic maps may be related structurally to the LaSalle Anticline.Indiana Department of Conservatio

Fortran Program for the Upward and Downward Continuation and Derivatives of Potential Fields

In 1960 Roland G. Henderson, of the U.S. Geological Survey, published a comprehensive system for computation of first and second derivatives of potential fields and the continuation of fields to levels above or below the plane of observation. In our study a Fortran IV program (HNDRSN2), based on Henderson's algorithm, uses map data digitized at an equally spaced grid interval. Output from program HNDRSN2 includes maps of the field continued upward or downward from one to five grid units and first and second derivative maps on the surface and on selected downward continued levels. Test cases demonstrate the reliability of the program in standard analyses of gravity and magnetic fields

Geophysical Computer Program 11

Program HYPOERR evaluates the performance of a small network of arbitrary seismic arrays in determining coordinates and times of seismic events. A linearized inversion following the method of Uhrhammer (1980)is performed for a layered velocity structure by determining the eigenvalues and eigenvectors of the partial derivatives of travel time for P and/or S phases with respect to hypocenter position and origin time for each station in the array. A series of covariance matrices is then obtained to evaluate statistical errors for a specified grid of hypocenter locations at any given depth. Contour plots can then be made of the matrix elements by using standard contouring software. Examples are given for ( 1) the case of a hypothetical quadrapartite array and (2) an actual eight-station ocean-bottom seismometer array deployed around the 95.5° W. Galapagos propagating-rift zone

Part 2. Power Spectral Analysis

Automatic (computer) correlation of geophysical logs is complicated by stratigraphic thickening (or stretch) from one area to another. Previous algorithms compute the stretch with repeated crosscorrelations of the original logs. Program SPECOR presented in this report uses crosscorrelation of the power spectra of the logs to identify the stretch factor between logs in one simplified operation. Computations are performed in the frequency domain with the scequency intervals transformed to a logarithmic scale. Interpolation is required to obtain equally spaced power spectra. Given the stretch, displacement or lag between wells is computed rapidly by correlation processes, without needing to rely on iterative procedures

Analysis of geophysical logs from the Hawaii Geothermal Project well

A 6445-foot test well was completed on April 27, 1976 in the Puna Area of Hawaii as part of an extensive project to investigate a geothermal reservoir for energy production. Because bottom hole temperatures exceeded 300°C, it was possible to run geophysical logs in the upper 3500 feet only. Study of conventional and induction resistivity, self potential, neutron, gamma ray, caliper, temperature, temperature differential and drilling rate logs show that porosity, permeability and fluid flow are qualitatively identified on the logs. Lithologic logs of sample cuttings taken at five- to ten-foot intervals (together with cores taken at approximately 700-foot intervals) substantiate preliminary findings of the porous and permeable zones. Although the logs investigated are above many of the zones of production, new information was obtained about the in-situ nature of permeability in Hawaiian basalts.Prepared for NATIONAL SCIENCE FOUNDATION, Grant GI-38319 and ENERGY RESEARCH AND DEVELOPMENT AGENCY, Grant EY-76-C-03-l093

Gravity and magnetic surveys in support of geothermal exploration on Maui, Hawaii

Maps and graphs includedDetailed gravity and magnetic land surveys were conducted on the island of Maui during the summer of 1980. Part I: the purpose of the study, its scope, and the geology of the area. Part II: the field methods used and the reduction of data to map and cross-section form. Part III: the data analysis to date. Four areas were mapped: Lahaina-Olowalu, Paia-Haiku, Hana, and Makena

Geophysical Computer Programs

A program ( FINITEG) uses the finite-element method to deal with problems commonly encountered in the study of terrestrial heat flow. FINITEG can provide transient and steady-state solutions to one heat-flow problem or combined problems related to relief, nonuniform surface temperature, transient surface temperature, inhomogeneous thermal properties, heat generation, igneous intrusion, sedimentation, and erosion. The theory of the relevant finite-element method, programming procedures, and test results are given to prove that the algorithm is correct. Numerical solutions agree to within 5 percent of the analytical solutions for the individual problems