Performing physical analogue experiments requires:
- deformation boxes and tables for the construction of the experiments
- engines to transfer the forces to the model layers
- materials that scale with natural rocks
- monitoring equipment that allows for the detailed analysis of the modelling results
Experiments can be built on tables or within deformation boxes. The latter are particularly suited for performing lithosphere-scale experiments, where the layers of the model lithosphere are placed on a liquid representing the asthenosphere. Movable walls within the deformation box are connected to engines that can move towards or away from each other leading to shortening or elongation of the model layers similar to what tectonic forces do in nature. The TecLab is equipped with 10 deformation boxes of various sizes.
Engines are used to create an artificial tectonic force acting on the layers of the models and to ensure that this force is applied at a constant rate. Most engines have one piston which can be connected to a deformation box, a backstop or a plastic sheet. The engine in Figure 2A below has two individually movable walls that can move in the same or in opposite directions. Using different engines or combining them gives the possibility to construct almost every possible tectonic setting.
Big engine for creating artificial tectonic forces on the analogue models.
Small engine for creating artificial tectonic forces on the analogue models.
In analogue experiments, materials are used that behave in a similar way than rocks do, which allows for scaling down the natural prototype (km scale) to convenient lab-scale (cm-m).
At relatively low temperatures ( in the shallow parts of the crust), most rocks deform in a brittle way, i.e. by breaking. We use granular materials such as dry quartz o feldspar sands as analogues for layers in the crust or lithosphere that deform by breaking leading to the formation of faults.
Rocks can also respond to applied forces by flow-type behaviour (ductile deformation) instead of breaking. This behaviour becomes important at higher temperatures in the crust or when the rock layers are intrinsically weak. A good example for the latter is rock salt. In analogue experiments, ductile rocks are represented by silicone putties with different densities and viscosities.
This apparatus is designed to determine the viscosity of the viscous materials we use in our experiments. The model material is initially placed in a cylindrical cup. A weight attached to a fine chord and suspended over pulley generates the force necessary to rotate the inner coni-cylindrical viscometer body and hence shear the material. Viscosity can then be calculated from the relationship between the applied stress and the measured shear strain rate.
To interpret the experimental results, we need to obtain data during and after the experiment. This is done by monitoring with cameras and scanners.
- 3D surface scanner
The 3D surface scanner is used to collect spatial date (XYZ-coordinates) of the model surface during the experiment. A projector displays lines on the experiment. Two cameras observe these lines and an 3D image of the model topography is created.
- Digital cameras
During the experiments, digital images are taken by cameras placed with top view and side view. These images are taken with a fixed time interval. Once the experiment is finished, cross sections are made by cutting through the model. Again, digital images are taken for later interpretation of the model.
It is not possible to make cross sections of the model during the experiment. This limitation is overcome by using medical CT-scanners, which enable to study the inside of experiment while it is running. Images of deformation affecting the model layers are made in the same way as scans of broken bones in the human body.
CT-scanner with experimental setup.
Cross section made by CT-scanner. Plastic sand was used to create horizons, detectable by the CT-scanner.
- Virtual Reality
High resolution 4D monitoring by using dynamic-photogrammetry was used to gain insight in the 4d-developed of analogue experiments. Virtual reality (VR) technology is used to analyse fully textured 3D models, including cross sections, with the purpose of understanding 3 dimensional aspects of deformation.
- Processing tools
- Visualisation/interpretation tools