The Effect of Fault Damage Zone on the Dynamics of Earthquake Ruptures: Experimental Observations

Natural faults are typically surrounded by a damage zone consisting of fractures of varying scales and geometries, which can significantly influence the dynamics of earthquake ruptures. Numerical studies have shown that damage can affect rupture parameters such as velocity, style, and extent. However, only a limited number of experimental studies have examined the effect of damage on the rupture process, focusing primarily on the rupture speed. Here, we present direct experimental observations on how damage geometry can affect earthquake rupture dynamics on a planar fault. We use polymethyl methacrylate (PMMA) specimens with a pre-cut planar fault and create damage near the fault with varying crack geometry and spacings using laser cutting technology. We generate spontaneously propagating shear ruptures along the main faults and image the rupture using an ultra-high-speed camera operating at one million frames per second. By employing Digital Image Correlation (DIC) techniques, we obtain detailed evolution maps of velocities, displacements, and strains associated with the propagation of the ruptures. Initial results demonstrate that damage zone characteristics can significantly influence the slip velocity, rupture style, and speed, including the transition from sub-Rayleigh to supershear velocities. Such results can offer valuable experimental observations on how damage zones influence earthquake rupture dynamics and deepen the understanding of the complex interplay between fault structures and rupture processes.