Rheologic testing of wet kaolin reveals frictional and bi‐viscous behavior typical of crustal materials

Abstract

[1] New rheological data for wet kaolin support its use in analog table-top experiments that simulate deformation of the Earth's crust. Creep tests at small strain reveal that wet kaolin (62-66% water by mass) exhibits both elastic and viscous deformation characteristic of a Burger's material. When sheared to failure, the shear strength is relatively insensitive to the strain rate. The shear strength appears sensitive to the amount of initial compaction within the rheometer, which may indicate a normal-stress dependency typical of frictional materials. Stepped velocity tests at large strain demonstrate velocity weakening rate and state frictional behavior after yielding. Because the wet kaolin exhibits deformation characteristic of both frictional materials and bi-viscous materials, this material is well suited to simulate a variety of crustal deformational processes in scaled analog experiments. Citation: Cooke, M. L., and N. J. van der Elst (2012), Rheologic testing of wet kaolin reveals frictional and bi-viscous behavior typical of crustal materials, Geophys. Res. Lett., 39, L01308,

Analogue earthquakes and seismic cycles: experimental modelling across timescales

“…It shows the more complex Burgers rheology controlled by the water content (Cooke and van der Elst, 2012). With viscosities in the range of 10 6 -10 7 Pa s and elasticities in the order of 10 kPa, relaxation times are rather long (up to 15 min) compared to the previously discussed materials limiting the applicability in seismotectonic scale models of seismic cycles.…”

How do horizontal, frictional discontinuities affect reverse fault-propagation folding?

“…As recalled earlier, the mechanical behavior of wet kaolin depends mainly on its water content and strain rate (e.g., Eisenstadt and Sims, 2005;Cooke and van der Elst, 2012). In this study we used a mixture of clay with a 60% water content by mass, resulting in a density of 1.65 g/cm 3 .…”

“…It follows that we may assume a cohesion in the range 50e120 Pa (Eisenstadt and Sims, 2005) and a friction coefficient of 0.6 (Henza et al, 2010). To ensure a proper rheological behavior during the experiments we adopted a 0.02 mm/s hanging wall speed (Cooke and van der Elst, 2012). As a natural target we assumed a rock with a density of 2.5 g/cm 3 and a cohesion in the range 10e20 MPa.…”

On the complexity of surface ruptures during normal faulting earthquakes: excerpts from the 6 April 2009 L'Aquila (central Italy) earthquake (<i>M</i><sub>w</sub> 6.3)

“…Recent studies compared results obtained using wet clay and dry sand (e.g., Eisenstadt and Sims, 2005;Withjack and Schlische, 2006;Withjack et al, 2007), highlighting differences and similarities. On the one hand, wet clay has been used extensively to analyze brittle deformation related to folding (e.g., Cloos, 1968;Withjack and Jamison, 1986;Withjack and Schlische, 2006;Henza et al, 2010;Miller and Mitra, 2011), and its effectiveness as analog material has been stressed recently by new rheological tests (Cooke and van der Elst, 2012). On the other hand, dry sand is the most commonly used material for modeling tectonic deformation (see Graveleau et al, 2012 for a review).…”

“…6); one remains fixed throughout the experiment, thus representing the footwall, whereas the other one is pulled by a stepper-motor simulating hanging-wall subsidence. The displacement rate was fixed at 0.005 mm s −1 , a strain rate that is considered appropriate for wet clay experiments (e.g., Cooke and van der Elst, 2012). The apparatus has the top and both sides free so as to prevent undesired boundary effects.…”