Potential of Electrical Resistivity Tomography to Detect Fault Zones in Limestone and Argillaceous Formations in the Experimental Platform of Tournemire, France |
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Authors: | C Gélis A Revil M E Cushing D Jougnot F Lemeille J Cabrera A De Hoyos M Rocher |
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Institution: | 1. DEI-SARG Department, Institute for Radiological Protection and Nuclear Safety, B.P. 17, 92262, Fontenay-aux-Roses Cedex, France 2. Department of Geophysics, Colorado School of Mines, 80401, Golden, CO, USA 3. INSU-CNRS LGIT, Université de Savoie, UMR 5559, Le Bourget du Lac, France 4. DSU-SSIAD Departmant, Institute for Radiological protection and Nuclear Safety, B.P. 17, 92262, Fontenay-aux-Roses Cedex, France
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Abstract: | The Experimental platform of Tournemire (Aveyron, France) developed by IRSN (French Institute for Radiological Protection
and Nuclear Safety) is located in a tunnel excavated in a clay–rock formation interbedded between two limestone formations.
A well-identified regional fault crosscuts this subhorizontal sedimentary succession, and a subvertical secondary fault zone
is intercepted in the clay–rock by drifts and boreholes in the tunnel at a depth of about 250 m. A 2D electrical resistivity
survey was carried out along a 2.5 km baseline, and a takeout of 40 m was used to assess the potential of this method to detect
faults from the ground surface. In the 300 m-thick zone investigated by the survey, electrical resistivity images reveal several
subvertical low-resistivity discontinuities. One of these discontinuities corresponds to the position of the Cernon fault,
a major regional fault. One of the subvertical conductive discontinuities crossing the upper limestone formation is consistent
with the prolongation towards the ground surface of the secondary fault zone identified in the clay–rock formation from the
tunnel. Moreover, this secondary fault zone corresponds to the upward prolongation of a subvertical fault identified in the
lower limestone using a 3D high-resolution seismic reflection survey. This type of large-scale electrical resistivity survey
is therefore a useful tool for identifying faults in superficial layers from the ground surface and is complementary to 3D
seismic reflection surveys. |
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