Dilatant Faults in Cohesive Materials: Introduction

Dilatant faults are important features in earth's crust, as they can form pathways for fluids like water, gas or oil. Understanding the evolution and structure of dilatant faults is therefore crucial when it comes to predicting fault seals, flow in reservoirs or the exploration of ore deposits. We adress this topic with numerical modeling (DEM), sandbox modeling and field work.

Projects within this field include

1. Transistion from dilatant to shear faults due to increasing confining pressure
2. Interaction of pre-existing joints and faults in dilatant fault-systems
3. 4D evolution of open fractures studied with incremental ct-scans
4. Evolution of dilatant faults in mechanically layered material
5. Numerical modeling of dilatant faults usind discrete element method

Analogue modeling of brittle cohesive rocks can be done with cohesive powders. We use hemihydrate powder (CaSO4 * 1/2 H2O), the mechanical  properties of which are well studied (van Gent et al, 2010).

For numerical modeling we use the discrete element method (DEM) that allows the formation of open fractures. The open source software Esys-Particle provides the platform to run these simulations.

Our field analogues are (1) the Needles Fault Zone of the Canyonlands National Park, Utah/USA. A set of subparallel grabens cuts through brittle, jointed sandstone and forms a series of grabens; (2) Faults in basalts around the Kilauea-volcano on Hawaii. Other well suited regions are the rift zones of Iceland and Afar.

Open fracture networks in CT-scanner


The analogue models of dilatant faults shown below are nice, but they have one major drawback, you cannot look INSIDE the models. Recently Marc Holland and Heijn van Gent have published on some first results of analogue models inside a CT-scanner, showig the 4D evolution of the open fracture networks in detail. The paper is available at EPSL (2011).

Open fractures in Gypsum


Msc-thesis, Heijn van Gent

Sandbox modeling has been used extensively over the last decades to study the structural evolution to model shallow geological processes. The materials used to date are however not well scaled for studying rocks with a high brittleness index, i.e. materials that are strong in comparison to the mean effective stress. Typically, materials like sand and clay do not develop brittle, dilatant structures observed in rocks like basalt and carbonate at shallow crustal depth.

In this work a scaled analogue model is presented, using a fine-grained, cohesive powder (CaSO4 • ½ H2O). Deformation experiments document material properties that allow scaling with respect to the natural prototypes. The tensile strength of the powder is approximately 40 Pa, depending on the state of consolidation.
Compression and shear tests show that the material parameters (Young’s modulus, cohesion, porosity) also depend
on the amount of consolidation/compaction, whereas the friction angle remains virtually constant. The behavior of these criteria allows analogue models of brittle rocks at scales between 1:1,500 and 1:600,000 depending on the properties of the prototypes carbonate or basalt. A model of a graben structure is presented using homogeneous or layered material sequences. In the layered sequences, sand and graphite/gypsum mixtures were used to decouple the layers forming a mechanical stratigraphy. Deformation is documented by time-lapse digital photography. These datasets are analyzed by Particle Imaging Velocimetry (PIV), which produces a high-resolution displacement field as a function of time and associated measures like strain or vorticity.

The results show – among others - mode-I fractures, mode-II faults with dilatant jogs, fragmentation processes in asperities, vertical gravity-driven mass transport along the fault zones, and the effect of mechanical stratigraphy. The structures formed show good resemblance with natural prototypes. The PIV output can be used for a high-resolution analysis of displacement and strain over time. Using the PIV output, elastic strain was observed prior to brittle failure, and the evolution of the fault array over time can be studied.

Dilatant faults in DEM models

Together with Steffen Abe, Discrete Element Models (DEM) are created to study the development of these open fractures numerically. One of the chalanges remains the the observation/identification of the fracture related prosity, but using the "Raytracer" extension of ESYS, developed by Stephan Tulkens, we are starting to get a grip on this.

Other articles in the category "Fault seals and top seals"





Michael Kettermann
The effect of preexisting joints on normal fault evolution : insights from fieldwork and analogue modeling. MSc thesis, supervised by Janos Urai, Heijn van Gent and Christoph Grützner (2011)
Heijn van Gent
Scaled analogue models of normal faulting in brittle lithologies, MSc-thesis, Geologie - Endogene Dynamik, RWTH Aachen University & Faculty of Earthsciences, University of Utrecht. (2005)
Marc Holland
Structure of fault zones in cohesive volcanic sequences. Diplomthesis. Geologie - Endogene Dynamik. (2004)


Heijn van Gent, Janos Urai, Marc Holland, Wanningen Erik
Sealing of Faults and Fractures by Clay Sediment on Jebel Hafeet - Field Observations and Modeling. Al Hajar, FEB2010 (16), 16-18. (2010)
Heijn van Gent, Marc Holland, Janos Urai
Open fractures in Sandbox experiments. In: Dynamics of complex intracontinental basins: The Central European Basin System. Littke, R., Bayer, U., Gajewski, D. & Nelskamp, S. (Eds). Springer-Verlag, Berlin-heidelberg, 520p. (2008)


Michael Kettermann, Janos Urai
Changes in structural style of normal faults due to failure mode transition: First results from excavated scale models. Journal of Structural Geology, Vol. 74, 105–116, doi:10.1016/j.jsg.2015.02.013 (2015)
Michael Kettermann, Christoph von Hagke, Janos Urai, Heijn van Gent
The interaction between pre-existing joints and normal faults in analogue models - implications for fault architecture and fracture connectivity; In: C. v. Hagke, J. Urai, K. Reicherter, F. Wellmann, C. Hilgers (Eds.). 20th Int. Conf. on Deformation Mechanisms, Rheology & Tectonics, Geotectonic Research 97 Special Issue, pp. 56-58 (2015)
Marc Holland, Heijn van Gent, Loic Bazalgette, Najwa Yassir, Eilard Hoogerduijn-Strating, Janos Urai
Evolution of dilatant fracture networks in normal faults - evidence from 4D model experiments. Earth and Planetary Science Letters 304: 399-406. (2011)
Steffen Abe, Heijn van Gent, Janos Urai
DEM Simulation of Normal Faults in cohesive Materials, Tectonophysics 512, 12-21. (2011)
Joyce Schmatz, Peter Vrolijk, Janos Urai
Clay smear in normal fault zones - the effect of multilayers and clay cementation in water-saturated model experiments Journal of Structural Geology 32 - Fault zones (11), 1834-1849. (2010)
Heijn van Gent, Marc Holland, Janos Urai, Ramon Loosveld
Evolution of fault zones in carbonates with mechanical stratigraphy - insights from scale models using layered cohesive powder. Journal of Structural Geology, Volume 32, Issue 9, Pages 1375-1391 (2010)
Marc Holland, Janos Urai, Stephen Martel
The internal structure of fault zones in basaltic sequences. Earth and Planetary Science Letters, 248(1-2),301 (2006)


Michael Kettermann, Christoph von Hagke, Simon Virgo, Janos Urai
Testing the influence of vertical, pre-existing joints on normal faulting using analogue and 3D discrete element models (DEM), Abstract Ref. Nr. EGU2015-11271 (2015)
Michael Kettermann, Janos Urai
Characteristic fault zone architectures as result of different failure modes: First results from scale models of normal faulting. EGU European Geosciences Union General Assembly, 27th April – 02nd May, 2014, Vienna (Austria). (2014)
Michael Kettermann, Janos Urai, Joschka Röth
How failure mode transition affects structural complexity in extensional graben settings: insights from excavated scale models. Geometry and Growth of Normal Faults. The Geological Society London, 23rd - 25th June, 2014. (2014)
Michael Kettermann, Joschka Röth, Janos Urai
Failure mode transition as result of effective stress – insights from analogue modeling using hemihydrate powder and sand. DEFORMATION MECHANISMS, RHEOLOGY & TECTONICS. KU Leuven 16-18 September 2013, Leuven, Belgium. (2013)
Michael Kettermann, Heijn van Gent, Christoph Grützner, Janos Urai
The effect of preexisting joints on normal fault evolution - Insights from field work and analogue modeling. TSK14 at Geomar, Kiel, 28.-30. 03. 2012 (2012)
Michael Kettermann, Heijn van Gent, Janos Urai
Modeling the effect of preexisting joints on normal fault geometries using a brittle and cohesive material. Geophysical Research Abstracts Vol. 14, EGU2012-4810, 2012 EGU General Assembly 2012 (2012)
Michael Kettermann, Sohrab Noorsalehi-Garakani, Heijn van Gent, Steffen Abe, Janos Urai, Marc Holland
Modeling of dilatant fractures in homogenous, cohesive material and in the presence of preexisting fractures. EGU General Assembly. Geophysical Research Abstracts, 13, pp. EGU2011-13519-1. Room 28 / Mon, 04 Apr, 11:15-11:30, oral. (2011)
Heijn van Gent, Steffen Abe, Janos Urai, Marc Holland
The formation of open fractures in brittle rocks and the evolution of permeability with fault slip- results from analogue and numerical models. EGU General Assembly 2009, Vienna, Austria, 19 - 24 April 2009, 11. (2009)
Steffen Abe, Heijn van Gent, Marc Holland
Discrete Element Simulations of the formation of open fractures during normal faulting of cohesive materials. Third International Geomodelling Conference, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Florence, Italy, September 22, 2008, (2008)
Steffen Abe, Heijn van Gent, Janos Urai
DEM Simulation of normal faulting in cohesive materials The 27th IUGG Conference on Mathematical Geophysics, Longyearbyen, Spitsbergen, Norway, June 15 - 20, 2008, 22. (2008)
Steffen Abe, Heijn van Gent, Janos Urai
Discrete Element Simulation of Normal Faulting In cohesive Materials. Geo 2008; International Conference and 106th annual meeting of the Deutsche Gesellschaft für Geowissenschaften e. V. (DGG) and 98th annual meeting of the Geologische Vereinigung e.V. (G (2008)
Martin P.J. Schöpfer, Conrad Childs, John Walsh, Steffen Abe, Arzu Arslan, Eoghan P. Holohan
Distinct Element Method (DEM) Modelling of Laboratory to Outcrop-Scale Fracturing of Natural Rocks. Joint Annual Meeting : GSA, ASA, CSSA, SSSA, GCACS, George R. Brown Convention Center, Houston, USA, 5-9 October, 129-4. (2008)
Heijn van Gent, Steffen Abe, Janos Urai, Marc Holland
The formation of open fractures in scaled analogue and numerical experiments. Third International Geomodelling Conference, Florence, Italy, September 23, 2008, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, 49, 338-342. (2008)
Heijn van Gent, Marc Holland, Janos Urai, Ramon Loosveld
The Internal Structure of Fault Zones in Carbonates Deformed at Shallow Crustal Level - Evidence From Scaled Physical Models Using Cohesive Powder. Eos Trans. AGU, 87(52),Fall Meet. Suppl., Abstract T23D-0531 (2006)
Heijn van Gent, Marc Holland, Janos Urai, Ramon Loosveld
Scaled Analogue Models of the Evolution of Normal Fault Systems in Carbonates. European Geosciences Union General Assembly, Vienna, 24-29 April 2005, 7, 401. (2005)
Marc Holland, Janos Urai, Stephen Martel
Internal Structure of Fault Zones in Mid-Oceanic-Ridges: Implications for habitat and fluid flow. AGU 2004 fall meeting, San Francisco, CA, United States, 3-9.12.2005, American Geophysical Union, 85 (52), V23C-08. (2004)
Joyce Schmatz, Marc Holland, Wouter van der Zee, Janos Urai
Fault gouge evolution in layered sand-clay sequences - first results of water-saturated sandbox experiments. Fault and Top Seals: What do we know and where do we go?, EAGE, Montpellier, France, 8-11 September 2003, O22. (2003)