HR: 15:45h
AN: NS53A-07    [Abstracts]
TI: Anisotropy Characterization of Fractured Crystalline Bedrock Using Asymmetric Azimuthal Geoelectric Techniques
AU: * Wishart, D N
EM: debonnewishart@yahoo.com
AF: Rutgers University, Department of Earth & Environmental Sciences 101 Warren Street Smith Hall 136, Newark, NJ 07102-1814, United States
AU: Slater, L D
EM: lslater@andromeda.rutger.edu
AF: Rutgers University, Department of Earth & Environmental Sciences 101 Warren Street Smith Hall 136, Newark, NJ 07102-1814, United States
AB: We examined the potential for geophysical characterization of fractured rock anisotropy by combining asymmetric configurations of azimuthal self potential (ASP) and azimuthal resistivity surveys (ARS), as previously demonstrated in the laboratory, at four field sites in the New Jersey Highlands (NJH) Province. There is a striking correlation between ASP measurements and fracture strike orientations at three of four sites investigated. ARS (electrical) data suggest three sites are overall heterogeneous and the fourth is anisotropic. The characteristic anisotropicity at the fourth site is controlled by a master structure; the NE-SW trending Lake Inez Fault Zone (LIFZ) that strikes at N10šE and parallels the Wanaque River to the east side of the site. Inferred groundwater flow directions are comparable to the (1) positive polarity (+ve) and magnitude of site-specific SP, (2) local surface drainage, and (3) also conformable with the regional northwest and northeast fracture trend of the NJH. The ASP is ineffective at one heterogeneous site where there is a lack of correlation between ASP and fracture strike data, probably due to poor drainage where there are no distinct paths of flow defined along fractures. Quantitative analysis of the magnitude of the energy observed in the odd and even coefficients of the power spectra of self potential (SP) datasets analyzed using a Fourier series was useful for characterizing anisotropic or heterogeneous flow in the fracture network. For anisotropic flow, the odd coefficients (harmonics) were close to zero, whereas heterogeneous flow resulted in significant energy in the odd coefficients. The employment of asymmetric geoelectric arrays has allowed this quantitative distinction between anisotropy and heterogeneity in fractured bedrock. The results of our study suggest the ability to quantify hydraulic anisotropy with azimuthal self potential and the distinction between electrically-anisotropic and electrically-heterogeneous in the subsurface. These results represent a significant advancement over the use of traditional resistivity arrays in site characterization of fracture- dominated systems.
UR: http:www.agu.org
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 5109 Magnetic and electrical properties (0925)
DE: 8010 Fractures and faults
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly