Geophysical and geological characterization of fractures within a granitic pluton

Abstract

Geophysical data have been acquired to characterize the fracture network of the surrounding volume within the FEBEX gallery (Grimsel Test Site, Aar granitic massif). The geophysical data include new borehole logging such as natural gamma and borehole televiewer and borehole ground‐penetrating radar (GPR). After processing an integrated interpretation of these different data sets, a pseudo three‐dimensional model of the distribution of fractures was constrained. Three main fracture planes nearly parallel to the axis of the FEBEX gallery have been interpreted. These features most probably provide the pathways for the water that contribute to the present hydrological flow regime. Presently, the tunnel is not sealed and acts as a water outflow point. The GPR images provided relative high amplitude events with a marked lateral correlation that was interpreted as two main fracture planes. The GPR is specially sensitive to the water content as it directly affects the electrical conductivity and the dielectric permittivity. Therefore, the fractures were considered as part of the conductive pathways through the crystalline rock.

3-D seismic travel-time tomography validation of a detailed subsurface model: a case study of the Záncara river basin (Cuenca, Spain)

“…Gypsum (CaSO 4 • 2H 2 O) is frequently affected by diagenetic processes and, as a consequence, gypsum rocks include clay, carbonates and other minerals. The presence of other minerals affects the purity of the gypsum rocks and this is reflected in changes of its physical properties potentially measurable with geophysical methods (Carmichael, 1989;Guinea et al, 2010;Festa et al, 2016). However, their variability in composition and their complex geometry make the characterization of these deposits challenging (Martinius et al, 2002;Diaz-Molina and Muñoz-Garcia, 2010;Escavy et al, 2012;Kaufman and Romanov, 2017).…”

3D Seismic Traveltime Tomography Validation of a Detailed Subsurface Model: The case study of the Zancara River Basin (Cuenca, Spain)

“…Depending on the target depth and the required spatial resolution different methodologies can be applied [e.g. Bryś et al, 2018;Novitsky, et al, 2018;Malehmir et al, 2009 andEscuder-Viruete et al 2004;Carbonell et al, 2010;Ogaya et al, 2016;Andres et al 2016, Alcalde et al, 2013b. Since the late 90's sophisticated geophysical techniques have been developed to estimate near-surface velocity models as a proxy for subsurface stiffness in seismic applications with different targets [Bergman et al, 2004 andHeincke et al, 2010].…”