Research by Prof. Dr. Boris Kaus
Lithospheric-scale shear localization
We have studied initiation of localized shear in visco-elasto-plastic materials, a rheology which is believed to be relevant for the deformation of the mantle lithosphere below the Moho. Previous (numerical) studies indicated that shear-heating may be an efficient mechanism to produce large-scale shearzones, potentially creating a subduction zone. The creation of subduction-zones is thought to be of primary importance in creating plate-tectonics on Earth. These previous models, however, used a large number of laboratory-derived parameters, and give therefore only a limited insight in the dynamics of the process. In particular it's unclear what controls whether localization occurs or not. It's also unclear how the uncertainties in laboratory data reflect itself in the localization process (does localization still occur if my effective viscosity is let's say 10% different?). Therefore we have performed an additional study with the help of over 100'000 0D, 1D and 2D numerical simulations, under different boundary conditions. Controlling parameters were identified and scaling laws were derived, which have predicitive power (i.e. rerunning the code is no longer necessary if your input parameters changes).
- Kaus B.J.P., Podladchikov Y.Y. (2006, in press). Initiation of localized shear zones in visco-elasto-plastic rocks. Journal of Geophysical Research.
Numerical modelling of brittle deformation at basin and crustal scale
Numerical modelling of faulting and brittle processes in the upper crust is a challenging problem, for which various solutions have been proposed in the geodynamic modelling community. I have developed numerical software that is capable of simulation large-strain deformation of brittle materials using viscoelasto rheologies in combination with non-associated Mohr-Coulomb plasticity. The results of different codes have been compared in a shortening and an extensional benchmark. Moreover, we are currently developing a new generation of benchmarks to further test the numerical codes.
- Buiter S.J.H., Babeyko A.Y., Ellis S., Gerya T.V., Kaus B.J.P., Kellner A., Schreurs G., Yamada Y. (2006). The numerical sandbox: Comparison of model results for a shortening and an extension experiment. in: Buiter, S.J.H. & Schreurs, G. Analogue and Numerical Modelling of Crustal-Scale Processes. Geological Society of London Special Publications, 253, 29-64.
- Buiter S.J.H., Kaus B.J.P., Mancktelow N.S. (2005) Discussion on designing a plasticity benchmark experiment. 9th International workshop on Numerical Modelling of Mantle Convection and Lithospheric Dynamics. Erice, Italy.
Lithospheric scale modeling of long-term tectonic processes
Lithospheric-scale modeling of tectonic processes is a useful tool that can help to develop a geological, geodynamical and mechanically consistent model for a given tectonic region. As part of a larger, NSF-funded project (TAIGER), PhD-student Clare Steedman is employing SloMo to get a deeper insight in processes that resulted in the formation of Taiwan. Current modelling efforts concentrate on a multiscale approach in which the interaction between lithospheric-scale and crustal scale processes studied.
- Steedman C.E., Kaus B.J.P., Okaya D., Becker T.W. (2005) Lithosphere-Scale modeling of the Taiwan Orogeny. Eos Trans. AGU, 86(52). Fall Meet Suppl., Abstract T11B-0370
Mineral phase transitions and large-scale tectonics
The density of rocks changes under elevated pressures and temperatures, partly due to the occurence of metamorphic phase transitions. Advances in metamophic phase petrology have brought us to a stage where experimentally obtained phase transitions can be reproduced to a fairly good accuracy with thermodynamical data. Thus we can couple these tools to large-scale geodynamic models, and by doing so one may discover fairly important effects of phase transitions on large-scale tectonics.
- Kaus B.J.P., Connolly J.A.D, Podladchikov Y.Y., Schmalholz S.M. (2005). The effect of mineral phase transitions on sedimentary basin subsidence and uplift. Earth and Planetary Science Letters. 233. p213-228.
- Perplith, a graphical user interface for Perple_X
Interaction between tectonics, erosion and gravity
Domal structures in compressional orogenies may be formed by a number of processes. We explore two of such processes, namely folding (caused by a viscosity difference and compression) and diapirism (due to a density instability) both under the influence of erosion. Whereas each of these processes seperately has been studied in large detail in a number of papers, the transitions between the different mechanism are less clear (sure, compression may overtake diapirism; but how much compression do I need exactly to overrun diapirism? And what if I use a different rheology?). Another particular interesting question is: can I distinguish the different mechanisms in the field? In order to answer these questions, we've used analytics, numerics and geological interpretation. It turns out that two non-dimensional parameters controll the model behavior and that we might indeed distinguish the mechanisms from field observations.
- Burg J-P., Kaus B.J.P., Podladchikov Y.Y. (2004). Dome structures in collision orogens. Mechanical investigation of the gravity/compression interplay, in: Whitney D.L., Teyssier C. and Siddoway C.S., Gneiss domes in orogeny: Boulder, Colorado, Geological Society of America Special Paper 360, p47-66.
3D folding and implications for the strength of the lithosphere
Compression of the lithosphere, sedimentary sequences or quartz veins may result in a folding instability, provided that the effective viscosity contrast between "strong" and "weak" layers is sufficiently large. Whereas this process of relatively well understood in 2D, little is known about the finite amplitude instability in 3D. In a project with Stefan Schmalholz, I performed one of the first 3D numerical simulations. We use the results of the simulations to develop a new finite amplitude equation that describes the development of 3D folds from infinitesimally small to large amplitudes. This solution catches most of the dynamics of the folding instability and hence makes further 3D simulations (almost) superfluous. The resulting patterns look fairly interesting. Moreover we find that the differential stress of the strong layer decreases with increasing deformation. Ijn other words: a "strong" layer (i.e. of high viscosity), may appear weak (have small differential stresses). This is a possible explanation of how a jelly-sandwich model of the continental lithosphere can exist that has only few earthquakes in the mantle lithosphere.
- Kaus B.J.P., Schmalholz S.M. (submitted) 3D Finite amplitude folding: implications for stress evolution of crustal and lithospheric deformation
Elasticity and lithospheric-scale deformation
Deformation of the lithosphere under compression has previously been mainly studied with quasi-viscous rheologies. Little systematic work has been performed on the wavelengths and modes of instability if the lithosphere has a visco-elastic or a visco-elasto-plastic rheology. Work with Stefan Schmalholz and Dani Schmid concentrates on exactly these effects as well as on the evolution of differential stress of such a lithosphere. Since this research indicated that elasticity may be important for compressional lithospheric-scale deformation, I became interested in whether it would change density-driven deformation such as lithospheric detachment or mantle convection. In a project in collaboration with Thorsten Becker we studied the effects of elasticity on the Rayleigh-Taylor instability. Is it important? It depends...
- Kaus B.J.P., Becker T.W. (submitted) Effects of elasticity on the Rayleigh-Taylor instability: implications for large-scale geodynamics. Geophysical Journal International.
Novel numerical techniques
Numerical modeling of geodynamic processes is a challenging topics, since we've to deal with large-deformations, large variations in material parameters, coupling of thermics and mechanics, free surface deformations, brittle (elasto-plastic) and creep-like (viscous) deformation simulataneously. Although a number of codes exists that claim to be able to do these things, they often have strengths in one area and weaknesses in some other area's. I believe there is still much room for improvement in this area. For some of the problems I'm interested in, software is not available, so I've developed several new codes, using a number of different numerical techniques (finite-difference, hybrid finite-difference/spectral, finite element, 2D/3D).
- Kaus B.J.P., Podladchikov Y.Y., Schmid D.W. (2004). Eulerian spectral/finite-difference method for large deformation modelling of visco-elasto-plastic geomaterials. Bolletino di Geofisica. Vol. 45. p346-349.
- Kaus B.J.P. (2004). Modelling approaches to geodynamic processes. PhD-thesis, ETH Zurich, Switzerland (24 Mb).
Forward and inverse modelling of diapirism and the Rayleigh-Taylor instability: implications for salt tectonics
If a fluid of higher density lies on top of a fluid of lower density, the system is unstable and the low density fluid wants to rise through the other fluid. This instability is called the Rayleigh-Taylor instability, and has a range of applications in geosciences (e.g. plumes, mantle convection, (possibly) salt-tectonics, subduction, lithospere deformation, magma migration, detachment of lower lithosphere...). We have studied this instability and in particular it's pattern formation in 3D.
- Kaus B.J.P., Podladchikov Y.Y. (2001). Forward and reverse modeling of the three-dimensional Rayleigh-Taylor instability. Geophysical Research Letters. Vol. 28, No 6. p1095-1098.
Fluids and earthquakes
Highly pressurized fluids that migrate through the Earth's crust may create their own permeability. In a project in collaboration with Steve Miller (Bonn University) we applied such a nonlinear model to the generation of an aftershock earthquake sequence in the Umbria region, Italy.
- Miller S.A., Collettinni C., Chiaraluce L., Cocco M., Barchi M., Kaus B.J.P. (2004). Aftershocks driven by a high pressure CO2 source at depth. Nature, Vol. 427. p724-727.
Physics of melt-migration
The details of how magma migrates through the earth's mantle, lithosphere and crust are not well understood. In an ongoing project we are analyzing the interaction between deformation and melt migration, as well as the transition from pervasive to focussed flow, through direct numerical simulations. Initial results show that the compaction equations result in pipe-like features, under the assumption that rocks are weaker in extension than under compression.