Schöpfer, Martin P. J.Martin P. J.SchöpferArslan, ArzuArzuArslanWalsh, John J.John J.WalshChilds, ConradConradChilds2011-07-192011-07-192011 Elsev2011-04Journal of Structural Geology0191-8141http://hdl.handle.net/10197/3026Natural and man-made brittle layers embedded in a weaker matrix and subjected to layer-parallel extension typically develop an array of opening-mode fractures with a remarkably regular spacing. This spacing often scales with layer thickness, and it decreases as extension increases until fracture saturation is reached. Existing analytical one-dimensional (1-D) 'full-slip' models, which assume that interfacial slip occurs over the entire length of the fracture-bound blocks, predict that the ratio of fracture spacing to layer thickness at saturation is proportional to the ratio of layer tensile to interface shear strength (T/s). Using 2-D discontinuum mechanical models run for conditions appropriate to layered rocks, we show that fracture spacing at saturation decreases linearly with decreasing T/s ratio, as predicted by 1-D models. At low T/s ratios (ca. <3.0), however, interfacial slip is suppressed and the heterogeneous 2-D stress distribution within fracture-bound blocks controls further fracture nucleation, as predicted by an existing 2-D 'fracture infill criterion'. The applicability of the two theories is hence T/s ratio dependent. Our models illustrate that fracture spacing in systems permitting interfacial slip is not necessarily an indicator of fracture system maturity. Fracture spacing is expected to decrease with increasing overburden pressure and decreasing layer tensile strength.13151692 bytes1763581 bytesapplication/octet-streamapplication/pdfenThis is the author’s version of a work that was accepted for publication in Journal of Structural Geology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Structural Geology Volume 33, Issue 4, April 2011, Pages 551-565 DOI#:10.1016/j.jsg.2011.01.008.Fracture spacingRock jointsShear lag modelDistinct element methodFracture mechanicsRock mechanicsJoints (Geology)Shear (Mechanics)Journal Article33455156510.1016/j.jsg.2011.01.008https://creativecommons.org/licenses/by-nc-sa/1.0/