UMass Geomechanics

Claybox Models of Fault System Evolution

Unlike the Earth, analog models allow us to directly observe the development of fault systems. The scale of the analog models is 5 orders of magnitude smaller than the crust so the strength of the clay needs to be 5 orders of magintude weaker than crustal rocks. With new techniques we are able to capture quantitative data from the experiments that facilitates comparison with numerical models and aids in our understnading of fault system evolution.

The experimental rig has two perpendicular (x-y) computer-controlled motors that provide unlimited movement of the right side of the deformation box.

A computer controls the movement of the motors and processes information from the laser scanner. The three-dimensional laser scan records detailed surface topography. The camera (above) takes pictures that can be analyzed to determine the evolution of the complete strain field during the experiment via PIV analysis.

Deformation near restraining bends

restraining bends

Within wet kaolin models we investigate the impact of fault spacing and overlap on the development of new faults around restraining bends within the claybox model.

Cooke, Michele L., Mariel T. Schottenfeld and Steven W. Buchanan, 2013. Evolution of Fault Efficiency at Restraining Bends within Wet Kaolin, Journal of Structural Geology, doi:10.1016/j.jsg.2013.01.010.

The red images are from the laser scan data.

With PIV we are able to track pixels in successive photos of the claybox and quantify detailed changes in the fault system.

Youtube channel with videos of our restraining bend experiments

piv

Development of normal faults

early in experiment
Early: Normal faults form over the stretching rubber from small air bubbles

later stage in experiment
Later : These faults grow in length and develop relay structures

Several decades ago, George Mc Gill devised an extensional experiment to simulate the development of the Canyonlands in sand layers over melting wax. The following image is from one of his experiments.

Clicking the image will download 3D PDF file of the sandbox surface. This interactive image can be viewed with Adobe Acrobat version 7.0 or later. Acrobat Reader allows you to manipulate and rotate 3D PDF images

grabens

Simulation of the Southern Big Bend of the San Andreas fault

clay experiment

Through the San Bernardino Mountains the San Andreas Fault apepars to have a complex 3D shape that changed over the evolution of the fault. In the last 1 million years, the San Andreas has abandonned two active strands. We examine these transitions with analog models.

monopoly houses not to scale