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USE OF SEISMIC REFRACTION TO DELINEATE AND CHARACTERIZE FRACTURES IN CARBONATE BEDROCK AND GLACIAL OVERBURDEN OF NORTHWEST OHIO
| Title: | USE OF SEISMIC REFRACTION TO DELINEATE AND CHARACTERIZE FRACTURES IN CARBONATE BEDROCK AND GLACIAL OVERBURDEN OF NORTHWEST OHIO |
| Author: | Nugent, Andrew Thomas |
| Description: | Methods were developed to locate and characterize fracture networks within carbonate bedrock and glacial overburden of northwest Ohio using seismic data collected in radial and grid arrangements. Two study areas were chosen to isolate the desired targets: a site with less than 1 m of overburden for bedrock fractures, and a site with over 10 m of overburden for overburden fractures. Data were collected with a Geometrics SmartSeis 24 channel Seismograph using a hammer as an energy source. Three methods were developed and evaluated, each of which is based on recognizable phenomena associated with the propagation of seismic energy across a discontinuity: arrival time delays, diffracted waves resulting from seismic wave scatter, and amplitude attenuation anomalies. Each of these methods was tested and confirmed with control surveys done over a bedrock pavement containing several fractures. The location and orientation of fracture traces were identified by noting the location(s) of fractures on individual seismic profiles, as determined by one or more of the three methods, and connecting them with fracture locations on adjacent profiles. The bedrock was found to have dominant fracture trends of 094° , 040° - 055°, and 122° - 135°. The overburden was found to have dominant fracture trends of 082° and 030° - 045°. These results are similar to those of Nolan (2000) and Dean et al. (1991). The overall success of the three methods used in conjunction with one another has proven to be quite useful. However, the results produced from the use of amplitude attenuation anomalies appear to be much more robust and alleviate much of the bias produced with the arrival-time delay and diffraction methods. Additionally, the radial arrangement of geophones proved to show better linear agreement from line-to-line then the grid arrangement. The overall success with using seismic methods to locate and characterize fracture networks within the subsurface has proven to be both cost and time-efficient, and when used in conjunction with other geophysical methods, can be an essential exploration tool. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1147205868
http://hdl.handle.net/2374.OX/15418 |
| Date: | 2006 |
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