Dilatant faults often form in rocks containing pre-existing joints, but the effects of joints on fault segment linkage and fracture connectivity is not well understood. We present an analogue modeling study using cohesive powder with pre-formed joint sets in the upper layer, varying the angle between joints and a rigid basement fault. We analyze interpreted map-view photographs at maximum displacement for damage zone width, number of connected joints, number of secondary fractures, degree of segmentation and area fraction of massively dilatant fractures. Particle imaging velocimetry helps provide insights on deformation history of the experiments and illustrate the localization pattern of fault segments. Results show that with increasing angle between joint-set and basement-fault strike the number of secondary fractures and the number of connected joints increases, while the area fraction of massively dilatant fractures shows only a minor increase. Models without pre-existing joints show far lower area fractions of massively dilatant fractures while forming distinctly more secondary fractures.

We performed scaled physical models of normal faulting in brittle rocks with pre-existing vertical joints. The angle between joint joint strike and strike of a pre-defined rigid basement fault was varied (JF-angle; 0°, 4°, 8°, 12°, 16°, 20°, 25°). We use Particle imaging velocimetry (PIV) to provide insights on deformation history and illustrate the localization pattern of fault segments. Especially plotting the divergence of the vector field is insightful, as it highlights local compression or extension, i.e. opening of joints. Analyses of interpreted map-view photographs at maximum displacement include damage zone width, number of connected joints, number of secondary fractures, degree of segmentation and area fraction of massively dilatant fractures.For each experiment three movies compiled from image series are provided, showing (1) top-view, (2) oblique view and (3) divergence of the displacement field derived from PIV analyses. Filenames are in the format - . (e.g. "JF-4deg-topview.mov"). Movies are in Apple QuickTime Format.

Supplement to: Kettermann, Michael; von Hagke, Christoph; van Gent, Heijn W; Grützner, Christoph; Urai, Janos L (2016): Dilatant normal faulting in jointed cohesive rocks: a physical model study. Solid Earth, 7(3), 843-856