AN EXPERIMENTAL-STUDY OF INCREMENTAL SURFACE LOADING OF AN ELASTIC PLATE - APPLICATION TO VOLCANO TECTONICS

Models of surface fractures due to volcanic loading of an elastic plat e are commonly used to constrain the thickness of planetary lithospher es, but discrepancies exist in predictions of the style of initial fai lure and in the nature of subsequent fracture evolution. In this study , we perform an experiment to determine the mode of initial failure du e to the incremental addition of a conical load to the surface of an e lastic plate and compare the location of initial failure with that pre dicted by elastic theory. In all experiments, the mode of initial fail ure was tension cracking at the surface of the plate, with cracks orie nted circumferential to the load. The cracks nucleated at a distance f rom load center that corresponds to the maximum radial stress predicte d by analytical solutions, so a tensile failure criterion is appropria te for predictions of initial failure. With continued loading of the p late, migration of tensional cracks was observed. In the same azimutha l direction as the initial crack, subsequent cracks formed at a smalle r radial distance than the initial crack. When forming in a different azimuthal direction, the subsequent cracks formed at a distance greate r than the radial distance of the initial crack. The observed fracture pattern may explain the distribution of extensional structures in ann ular bands around many large scale, circular volcanic features.