Articles | Volume 7, issue 3
https://doi.org/10.5194/se-7-843-2016
https://doi.org/10.5194/se-7-843-2016
Research article
 | 
27 May 2016
Research article |  | 27 May 2016

Dilatant normal faulting in jointed cohesive rocks: a physical model study

Michael Kettermann, Christoph von Hagke, Heijn W. van Gent, Christoph Grützner, and Janos L. Urai

Abstract. Dilatant faults often form in rocks containing pre-existing joints, but the effects of joints on fault segment linkage and fracture connectivity are 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 provides insight into the deformation history of the experiments and illustrates 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 increase, 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.

Download
Short summary
We present an analogue modeling study on the interaction of pre-existing joints and normal faults using cohesive powder. We vary the angle between joints and a rigid basement fault and analyze interpreted map-view photographs at maximum displacement for various parameters and compare to nature. Results show a clear effect of increasing angle between joints and faults on fault geometry, fracture density and connectivity. These information can help interpreting fractured layers in the subsurface.