Experimental Modeling of En Masse Translation of Long Brittle Blocks Over a Viscous Layer: Application to the Sichuan Basin, China

Abstract Although a significant number of studies on thrust nappes exists, analog modeling addressing the formation mechanisms of en masse (no internal strain) translation of long brittle blocks remains scarce. Furthermore, our understanding of its underlying physics remains incomplete. This study employs a brittle/viscous model using quartz sand overlying silicone putty to investigate the influence of piston velocity, sand thickness and density, and vertical position of the piston's base on the transport of a thrust nappe. The results indicate that: (a) the distance traveled by a brittle block is influenced by all tested parameters; (b) there is an inverse linear relation between piston velocity and sand horizontal displacement, meaning that fast shortening hampers the far‐traveling of brittle blocks; (c) the higher the density of the brittle block the longer its transport, which is the opposite of what is theoretically expected; (d) there is an exponential relation between sand thickness and its transport, in contrast to the direct linear relation found theoretically; (e) for the same shortening velocity and sand density, the maximum transport distance is achieved for a piston whose base lies ∼6 mm below the brittle/viscous contact. Our analog modeling shows that en masse transport is possible when brittle layer strength is higher than underlying viscous layer strength, which provides new insights into the origin and dynamics of the Sichuan Basin in China.