Analisi della propagazione d’onda e delle condizioni di sollecitazione nella fase di nucleazione di rotture di Modo II durante terremoti in scala

It is important to understand the mechanisms that concern earthquakes generated by human activity. While usually the interest lays on the later stages of rupture propagation, it is noteworthy to focus the attention on the nucleation phase of a shear rupture, which can model earthquakes. A way to study the phenomenon is through scaled laboratory earthquakes, in which dynamic shear ruptures are generated through the sublimation of a wire embedded in the lower half of a PMMA plate, which has a certain interface angle and is loaded uniaxially. Through an experimental analysis, dilatational waves are traced with digital image correlation and the stress state at the interface is investigated during the nucleation of the shear rupture. It emerges that the nucleation phase is independent of interface angle and frictional properties. In addition, by means of a tridimensional finite element analysis, a spatio-temporal variation of the interface-normal stress is imposed using data obtained from the experiment to simulate the perturbation caused by the wire explosion. Outside the perturbed region, it appears that the finite element model partially simulates the rupture: the supershear rupture velocity is the same but the interface-parallel velocity peak is smaller. To capture the rupture behaviour in the perturbed region, the results suggest that a smaller but stronger perturbation is necessary. Ultimately, the tridimensional simulation reveals that there is slip in the direction perpendicular to the surface of the specimen.