The sparsely spaced highly permeable fractures of the granitic rock aquifer at Stang-er-Brune (Brittany,
France) form a well-connected fracture network of high permeability but unknown geometry. Previous work
based on optical and acoustic logging together with single-hole and cross-hole flowmeter data acquired in 3
neighbouring boreholes (70-100 m deep) has identified the most important permeable fractures crossing the
boreholes and their hydraulic connections. To constrain possible flow paths by estimating the geometries of
known and previously unknown fractures, we have acquired, processed and interpreted multifold, single- and
cross-hole GPR data using 100 and 250 MHz antennas. The GPR data processing scheme consisting of timezero
corrections, scaling, bandpass filtering and F-X deconvolution, eigenvector filtering, muting, pre-stack
Kirchhoff depth migration and stacking was used to differentiate fluid-filled fracture reflections from source generated
noise. The final stacked and pre-stack depth-migrated GPR sections provide high-resolution images
of individual fractures (dipping 30-90°) in the surroundings (2-20 m for the 100 MHz antennas; 2-12 m for
the 250 MHz antennas) of each borehole in a 2D plane projection that are of superior quality to those obtained
from single-offset sections. Most fractures previously identified from hydraulic testing can be correlated to
reflections in the single-hole data. Several previously unknown major near vertical fractures have also been
identified away from the boreholes.