A PHYSICAL MODEL OF NEAR-HOMOGENEOUS 1-D HORIZONTAL SHORTENING OR STRETCHING OF A ~2-D LAYER
One edge of the elastic cloth is fastened firmly to a base made of melamine-covered fiberboard, and the opposite edge has a casing or rod pocket through which is fitted a steel rod ~3-5 mm in diameter. Smaller, student models can use foam board in place of the melamine board. We use dry powder (joint compound used for taping and skim-coating gypsum-board walls, widely available at home-improvement stores) to simulate the crust. Dry powder produces cracks or true faults, as contrasted with sand that deforms by inter-granular sliding and flow. Dry flour is an alternative to joint compound, but its disadvantages include  potential contamination of a classroom that might be harmful to gluten-intolerant students, and  the attraction of hungry vermin. Sometimes we use a thin layer of dry sand overlain by a thin layer of dry powder.
Placing a uniform thin layer of powder on the elastic fabric and then stretching the fabric by pulling on the steel rod produces a set of mode I cracks in the layer. Placing the powder on stretched fabric and letting the fabric relax and shorten produces multiple small reverse faults. Various simple modifications of the model produce interesting results that can lead to student-initiated discovery learning.