Evaluation of geophysical methods for locating subsurface hazards in the Shawnee National Forest.
Jessop-JA; Hauser-KL; Gese-DD
Abstract Book, U.S. Department of the Interior Conference on the Environment and Safety, April 24-28, 1995. Washington, DC: U.S. Bureau of Mines, 1995 Apr; :26
The Bureau of Mines initiated a subsidence study in the Shawnee National Forest in Southern Illinois with the U.S. Forest Service. Two sites were chosen from a Bureau study which identified 200 inactive tripoli mine sites and subsidence holes. Reconnaissance geophysical investigations were carried out to determine specific methods for detection of subsurface openings. Magnetic gradient, ground penetrating radar (GPR) and high resolution seismic survey were conducted at chosen sites. Preliminary results identified a subsurface opening based on disturbed wave patterns observed in the GPR and seismic records. The magnetic gradient profiles show variations of 5 to 10 gamma per meter changes over undermined areas. The ground penetrating radar signal shows a single frequency, high amplitude "ringing" effect when data are recorded over know underground workings. GPR data recorded over unmined areas typically show higher frequency signals due to reflections from structural and lithologic features. This pronounced effect is observed in the GPR profiles. The seismic data were collected in a common mid-point (CMP) method from which common offset profiles were generated. These profiles show disturbances in the first breaks over undermined areas. Comparison of the geophysical records provides the best method for proper interpretation of the data.
Geophysics; Occupational-hazards; Hazards; Forestry; Mining-industry; Underground-mining; Geology
Conference/Symposia Proceedings; Abstract
U.S. Bureau of Mines