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Analogue modeling #1
Analogue modeling (Fig.1) is a technique in which artificial/laboratory materials are employed to simulate the mechanical behavior of deforming rocks in nature.
Two types of materials are generally used: frictional materials (e.g. sand and other finer powders), to simulate the brittle (Coulomb-Mohr) behavior of upper crustal rocks; and viscous materials (e.g. different types of silicone putties, plasticine, honey, glycerin, etc.) to simulate the ductile behavior of middle crustal rocks or the asthenosphere.
The main limitation of analogue modeling is its incapacity of thoroughly reproducing the thermo-mechanical properties of natural rocks; things like geo-thermal or pressure gradients of the lithosphere for instance, are impossible to directly ascribe to analogue models.
However, the choice of materials with the proper scaled rheological properties can (and often does) provide a very good approximation of the natural example at stake.
The great advantage of analogue modeling is the 3D insight that it easily provides when compared with the difficult that such three dimensional approach still poses in numerical modeling.
Modeling of natural geological processes is thus probably going to be increasingly based on a coupled approach, encompassing both analogue modeling, to get a first more qualitative 3D insight on what’s going on, and a numerical approach to obtain more detailed generalizations.
I will be posting photos of analogue models of wrenching, thrusting and extensional tectonic structures obtained in the LATTEX-IDL Analogue Modeling Lab (Univ. of Lisbon).
The photos on the left (Fig.2) concern wrenching and thrusting. They depict a sand-box analogue model of the morpho-tectonic pattern that characterizes the interference between a dextral strike-slip fault (along the length of the photo), and several thrusts (facing the observer, oblique to the strike-slip fault). Note the several subsidiary structures (like Riedel faults – R’) that are theoretically expected to form in a brittle medium. For comparison an aerial photo of the San Andreas fault is also included (San Andreas Fault in the Carrizo Plain, aerial view from 8500 feet altitude, author and copyright holder Ikluft, photo obtained in Wikipedia here).