Finding the strike direction of fractures using GPR

Abstract

GPR reflection energy varies with antenna orientation relative to the strike and dip of the reflector. This directional dependence of GPR responses was investigated through numerical experiments and was used to estimate the azimuth of fractures and joints. Three antenna configurations were considered in this study: perpendicular‐broadside (YY mode), parallel‐broadside (XX mode) and cross‐polarization (YX mode). The reflection energy in the cross‐polarization mode shows a shape characteristic similar to the strike, regardless of the dip angle. Those in the other two modes show quite different amplitudes from the strike, depending on the dip angle. We have developed a strike‐direction‐finding scheme using data obtained from the three different modes for the same survey line. The azimuth angle of each reflector was displayed in colour on the GPR profile. This scheme was applied to a field survey at a granite quarry in southern Korea. The GPR profiles showed different images of the reflectors depending on the antenna configuration. The estimated azimuths of reflectors obtained using our scheme matched fairly well with those of known fractures and joints.

Ground-penetrating-radar response to fracture-fluid salinity: Why lower frequencies are favorable for resolving salinity changes

“…Flow through this highly heterogeneous medium is controlled by fracture aperture, channeling along the fracture ͑i.e., aperture variability͒, and fracture connectivity. Ground-penetrating radar ͑GPR͒ is a suitable near-surface geophysical method for detecting and imaging fractures ͑Davis and Annan, 1989;Grasmueck, 1996;Seol et al, 2001;Tsoflias et al, 2004;Jeannin et al, 2006͒. Surface reflection and borehole tomography studies relate GPR signal amplitude to fracture aperture and fluid content ͑Lane et al, 1998; Lane et al, 2000;Grégoire et al, 2003;Grégoire and Hollender, 2004͒.…”

Multiconfiguration GPR measurements for geometric fracture characterization in limestone cliffs (Alps)

“…Similarly, Toshioka et al (1995) detected the distribution and continuity of cracks from GPR data acquired on the vertical wall of a welded tuff rock. Seol et al (2001) developed a strike-direction-finding scheme using GPR data obtained from three different acquisition modes for the same survey line in a granite quarry. The computed reflector azimuths were found to be closely correlated to those of observed fractures and joints.…”

Tools and Techniques: Ground-Penetrating Radar

“…Van Gestel and Stoffa (2001) and Seol et al (2001) had used the Alford rotations of 2-D multicomponent GPR to determine the strike direction of fractures. Sassen and Everett (2009) developed a polarimetric coherency algorithm that is based on the eigenvalue decomposition of the scattering matrix and applied on multicomponent GPR data recorded over a karstic limestone exhibiting a high degree of fracturing.…”