Browsing by Author "Blakely, Robert F."

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Computer Calculation of Two-Dimensional Gravity Fields
(Indiana Geological & Water Survey, 1983) Blakely, Robert F.; Rudman, Albert Julius
In 1959 Talwani and others published an algorithm to compute the gravitational field of an arbitrarily shaped two-dimensional body (finite cross section and infinite horizontal extent). A Fortran program GRAV2D presented in this report follows the line-integral method developed by Talwani and his coauthors. Input may consist of one or more bodies; output may be computed at any elevation and distance. Two test cases demonstrate the reliability of the program.
Fortran Program for Correlation of Stratigraphic Time Series
(Indiana Geological Survey, 1978) Kwon, Byung-Doo; Blakely, Robert F.; Rudman, Albert, J.
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 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.
Fortran Program for Generation of Earth Tide Gravity Values
(Indiana Geological & Water Survey, 1977) Blakely, Robert F.; Rudman, Albert Julius; Ziegler, Robert
A summary of formulas for calculation of tidal accelerations due to the moon and the sun were compiled for computer use by I.M. Longman in 1959. On the basis of Longman's formulas we developed a Fortran IV program (PRETID) to predict tides for specified time intervals at any point on the surface of a rigid earth. Output from the program PRETID consists of a printout of tidal values in milligals with a corresponding line printer plot. Test cases comparing results with standard EAEG (European Association of Exploration Geophysicists) tables show reliability of the program.
Fortran Program for Generation of Synthetic Seismograms
(Indiana Geological & Water Survey, 1976) Blakely, Robert F.; Rudman, Albert Julius
"A Fortran IV computer program to generate synthetic seismograms has been developed by using the reflection coefficients computed for layers with differing velocities v. Convolution of coefficients with an input wave yields the synthetic seismogram. Choice of the input wave depends on what the user considers to be the best approximation of the response of his seismic system to a reflection. Input to the program consists of depths and interval transit times digitized from a continuous velocity log. Output consists of (1) a table of depths, transit times, interval velocities, reflection coefficients, and amplitudes of the synthetic seismogram and (2) line-printer and Calcomp plots of the input wave and seismogram. Although this program is applicable in most geologic situations, there is no provision for including multiple reflections or energy attenuation."
Fortran Program for Reduction of Gravimeter Observations to Bouguer Anomaly
(Indiana Geological & Water Survey, 1977) Blakely, Robert F.; Rudman, Albert Julius; Kwon, Byung-Doo
A Fortran computer program was developed to reduce field results of gravimeter measurements to useful Bouguer gravity values. The program is able to reduce data that have been observed at widely varying times. Corrections have been made for (1) tide, (2) latitude, (3) instrument drift, (4) free air, and (5) Bouguer. Input to the program consists of observation times, original gravimeter readings and identification, location, and elevation of stations. Output consists of input data and corrected gravity values (the Bouguer anomaly). Contributions of each correction may also be printed. Plots showing station locations and corrected gravity values have been plotted in map form.
Seismic velocities and synthetic seismogram computed from a continuous velocity log of a test well to the basement complex in Lawrence County, Indiana
(Indiana Geological & Water Survey, 1960) Biggs, Maurice E.; Blakely, Robert F.; Rudman, Albert Julius
The Seismicity of Indiana Described by Return Periods of Earthquake Intensities
(Indiana Geological & Water Survey, 1976) Blakely, Robert F.; Varma, Madan M.
"The application of the statistics of extremes to seismic intensity values in Indiana allows the contouring of return periods for specific earthquake intensities. The contours show a region of low seismic activity running NW-SE through the center of the state; seismically, the quietest part of Indiana is Newton County. The highest seismic activity is recorded in the southwest corner of the state. The return periods for seismic events of intensity IV range from 20 to 45 years. Intensity VI events (slight damage) have return periods ranging from 80 to 240 years. Return periods for earthquakes rated intensity VII (moderate damage) range from 300 to 1,300 years. Higher intensities are not probable in Indiana, and therefore earthquake accelerations greater than 0.1 g are improbable."