Mapping fractures with GPR: A case study from Turtle Mountain

Abstract

Ground-penetrating radar (GPR) surveys were acquired of rocks on the highly fractured summit of Turtle Mountain in Canada. In 1903 a disastrous rock slide occurred at Turtle Mountain and it still poses a geologic hazard. Dips, shapes, and penetration depths of fractures are important parameters in slope-stability analysis. Determination of fracture orientation at Turtle Mountain has been based mostly on areal geologic mapping and, most recently, on data collected from boreholes. The purpose of GPR surveys was to test, confirm, and extend information about fractures and bedding planes. Data acquisition was complicated by the rough terrain; because slopes are steep and uneven. This also complicated analysis of the data. Measurement of in situ velocity — an important value for migration — was impossible. Instead, data were migrated with different velocities and data results were chosen that were considered to be reasonable. Analysis and interpretation of the data, resulted in confirmation and extension of the a priori information on orientations of fractures and bedding planes at Turtle Mountain. Despite the rough terrain and highly fractured rock mass, GPR surveys provide reliable information about the shapes and density of fractures — information important for slope-stability evaluation. The most reliable migration results obtained for velocities were considerably less than the standard velocities recorded for limestone, the dominant lithofacies at Turtle Mountain. We interpret this observation as an indicator of water within the rock. However, thorough investigation of this conclusion remains a project for future work.

Geophysical investigation of the Sandalp rock avalanche deposits

“…For old rock avalanches, geophysical methods can contribute to retrieve information on both the rupture and deposits zones (McGuffey et al, 1996;Green et al, 2006;Jongmans and Garambois, 2007). Seismic and GPR (ground penetrating radar) prospecting have mainly been used to investigate rupture zones of old large rock avalanches like the 1911 Ananevo rock slide (Kyrgyzstan ; Havenith et al, 2002), the 1903 Turtle Mountain rock slide (Canada; Theune et al 2006) and the 1991 Randa event (Switzerland; Heincke et al, 2006;Spillmann et al, 2007), or rock avalanche prone slopes (Pettinelli et al, 1996;Ferrucci et al, 2000;Méric et al, 2005;). These surveys are aimed at delineating potentially unstable slopes by mapping fractures (with GPR) and identifying zones of low seismic velocity (altered rocks with fractures).…”

Imaging and characterization of a carbonate hydrocarbon reservoir analogue using GPR attributes

“…Carbonate rocks normally exhibit relatively low attenuation and are therefore a privileged material for GPR applications (Sengwa and Soni, 2006). Several authors have focused on objectives such as detection of caves and karstic features (Al-fares et al, 2002;Chamberlain et al, 2000;Kruse et al, 2006), localization, mapping and characterization of fractures and faults (Grasmueck et al, 2005a,b;Jeannin et al, 2006;McClymont et al, 2008;Pipan et al, 2003a,b;Theune et al, 2006), geomechanical and engineering applications (Corin et al, 1997;Orlando, 2003;Pettinelli et al, 1996) and stratigraphy imaging (Davis and Annan, 1989;Grasmueck and Weger, 2002). GPR datasets collected close to limestone outcrops have been used as analogues for hydrocarbon reservoirs (Grasmueck et al, 2005a,b;Takayama et al, 2008).…”

Geophysical Investigations of Soil–Landscape Architecture and Its Impacts on Subsurface Flow

“…Hubbard et al (2005) and Rubin and Hubbard (2006) have summarized the use of GPR to estimate water content, hydraulic conductivity, geochemistry, and lithofacies zonation. Ground-penetrating radar has been used extensively to chart bedrock depths (Collins et al, 1989;Davis and Annan, 1989), changes in rock type (Davis and Annan, 1989), fractures, joints, bedding, and cleavage planes (Nascimento da Silva et al, 2004;Pipan et al, 2000;Porsani et al, 2005;Theune et al, 2006), and faults (Demanet et al, 2001). Bedrock restricts, redirects, and concentrates the infiltration of water.…”

“…The depth to bedrock and the topography of the bedrock surface affect the subsurface flow of water. Ground-penetrating radar has also been used to study fractures, unloading or exfoliation joints, bedding and stress planes, and cavities of the underlying bedrock (Theune et al, 2006;Porsani et al, 2005;Al-fares et al, 2002). Ground-penetrating radar has been used extensively to chart bedrock depths (Collins et al, 1989;Davis and Annan, 1989), changes in rock type (Davis and Annan, 1989), fractures, joints, bedding, and cleavage planes (Nascimento da Silva et al, 2004;Pipan et al, 2000;Porsani et al, 2005;Theune et al, 2006), and faults (Demanet et al, 2001).…”